ALBERT

Description: Abstract Although it is established that there exist potential trade‐offs between grain yield and grain quality in wheat exposed to elevated carbon dioxide (CO2) and ozone (O3), their underlying causes remain poorly explored. To investigate the processes affecting grain quality under altered CO2 and O3, we analysed 57 experiments with CO2 or O3 exposure in different exposure systems. The study covered 24 cultivars studied in 112 experimental treatments from 11 countries. A significant growth dilution effect on grain protein was found: a change in grain yield of 10% by O3 was associated with a change in grain protein yield of 8.1% (R2=0.96), while a change in yield effect of 10% by CO2 was linked to a change in grain protein yield effect of 7.5% (R2=0.74). Superimposed on this effect, elevated CO2, but not O3, had a significant negative effect on grain protein yield also in the absence of effects on grain yield, indicating that there exists a process by which CO2 restricts grain protein accumulation, which is absent for O3. Grain mass, another quality trait, was more strongly affected by O3 than grain number, while the opposite was true for CO2. Harvest index was strongly and negatively influenced by O3, but was unaffected by CO2. We conclude that yield vs. protein trade‐offs for wheat in response to CO2 and O3 are constrained by close relationships between effects on grain biomass and less than proportional effects on grain protein. An important and novel finding was that elevated CO2 has a direct negative effect on grain protein accumulation independent of the yield effect, supporting recent evidence of CO2‐induced impairment of nitrate uptake/assimilation. Finally, our results demonstrated that processes underlying responses of grain yield vs. quality trade‐offs are very different in wheat exposed to elevated O3 compared to elevated CO2.

Description: Rapid population growth and economic development have led to increased anthropogenic pressures on the Tibetan Plateau, causing significant land cover changes with potentially severe ecological consequences. To assess whether these pressures are also affecting the remote montane-boreal lakes on the SETibetan Plateau, fossil pollen and diatom data from two lakes were synthesised. The interplay of aquatic and terrestrial ecosystem response was explored in respect to climate variability and human activity over the past 200 years. Non-metric multidimensional scaling and procrustes rotation analysis were undertaken to determine whether pollen and diatom responses in each lake were similar and synchronous. Detrended canonical correspondence analysis was used to develop quantitative estimates of compositional species turnover. Despite instrumental evidence of significant climatic warming on the southeastern Plateau, the pollen and diatom records indicate very stable species composition throughout their profiles and show only very subtle responses to environmental changes over the past 200 years. The compositional species turnover (0.36-0.94 SD) is relatively low in comparison to the species reorganisations known from the periods during the mid- and early-Holocene (0.64-1.61 SD) on the SE Plateau, and also in comparison to turnover rates of sediment records from climate - sensitive regions in the circum-arctic. Our results indicate that climatically-induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem in our study area. Synergistic processes of post Little Ice Age warming, 20 th century climate warming and extensive reforestations since the 19 th century have initiated a change from natural oak-pine forests to semi-natural, likely less resilient pine-oak forests. Further warming and anthropogenic disturbances would possibly exceed the ecological threshold of these ecosystems and lead to severe ecological consequences.

Description: Combining a climatic envelope modeling technique with more than two centuries (1800-2009) of distribution records has revealed the effects of a changing climate on the egg-laying monotreme, the platypus, Ornithorhynchus anatinus . We show that the main factor associated with platypus occurrence switched from aquatic habitat availability (estimated by rainfall) to thermal tolerances (estimated by annual maximum temperature) in the 1960's. This correlates directly with the change in the annual maximum temperature anomaly from cooler to warmer conditions in southeastern Australia. Modeling of platypus habitat under emission scenarios (A1B, A2, B1 and B2) revealed large decreases (〉 30%) in thermally suitable habitat by 2070. This reduction, compounded by increasing demands for water for agriculture and potable use, suggests that there is real cause for concern over the future status of this species, and highlights the need for restoration of thermal refugia within the platypus’ modeled range.

Description: Anthropogenically-mediated decreases in pH, termed ocean acidification (OA), may be a major threat to marine organisms and communities. Research has focussed mainly on tropical coral reefs, but temperate reefs play a no less important ecological role in colder waters, where OA effects may first be manifest. Here, we report that trends in pH at the surface of three ecologically-important cold-water calcifiers (a primary producer and herbivores), under a range of fluid flows, differ substantially from one another, and for two of the three calcifiers the pH, during darkness, is lower than the mean projected pH due to OA for the surface waters of the global ocean beyond the year 2100. Using micro-optodes, we show that each calcifier had a different pH gradient between its surface and mainstream seawater, i.e. within the diffusion boundary layer which appears to act as an environmental buffer to mainstream pH. Abalone encountered only mainstream seawater pH, whereas pH at the sea urchins’ surface was reduced by ~0.35 units. For coralline algae, pH was ~0.5 units higher in the light and ~0.35 units lower under darkness than in ambient mainstream seawater. This wide range of pH within the DBL of some calcifiers will probably affect their performance under projected future reductions in pH due to OA. Differing exposure to a range of surface pH may result in differential susceptibility of calcifiers to OA. Such fluctuations are no doubt regulated by the interplay of water movement, morphology and metabolic rates (e.g. respiration, calcification and/or photosynthesis). Our study, by considering physics (flow regime), chemistry (pH gradients versus OA future projections) and biology (trophic level, physiology and morphology), reveals that predicting species-specific responses and subsequent ecosystem restructuring to OA is complex and requires a holistic, ecomechanical, approach.

Description: Maximum and minimum soil temperatures affect belowground processes. In the past 50 years in arid regions, measured reductions in the daily temperature range of air (DTR air ) most likely generated similar reductions in the unmeasured daily temperature range of soil (DTR soil ). However, the role of DTR soil in regulating microbial and plant processes has not been well described. We experimentally reduced DTR soil in the Chihuahuan Desert at Big Bend National Park over 3 years. We used shade cloth that effectively decreased DTR soil by decreasing daily maximum temperature and increasing nighttime minimum temperature. A reduction in DTR soil generated on average a two-fold increase in soil microbial biomass carbon (MBC), a 42% increase in soil CO 2 efflux and a 16% reduction in soil NO 3 - -N availability; soil available NH 4 + -N was reduced by 18% in the third year only. Reductions in DTR soil increased soil moisture up to 15% a few days after a substantial rainfall. Increased soil moisture contributed to higher CO 2 efflux, but not MBC, which was significantly correlated with DTR soil . Net photosynthetic rates at saturating light ( A sat ) in Larrea tridentata was not affected by reductions in DTR soil over the 3-year period. Arid ecosystems may become greater sources of C to the atmosphere with reduced DTR soil , resulting in a positive feedback to rising global temperatures, if increased C loss is not eventually balanced by increased C uptake. Ultimately, ecosystem models of N and C fluxes will need to account for these temperature-driven processes.

Description: European forests are an important carbon sink, yet the relative contributions to this sink of climate, atmospheric CO2 concentration ([CO2]), nitrogen deposition and forest management are under debate. We attributed the European carbon sink in forests using ORCHIDEE-FM, a process-based vegetation model that differs from earlier versions of ORCHIDEE by its explicit representation of stand growth and idealized forest management. The model was applied on a grid across Europe to simulate changes in the net ecosystem productivity (NEP) of forests with and without changes in climate, [CO2] and age structure, the three drivers represented in ORCHIDEE-FM. The model simulates carbon stocks and volume increment that are comparable – RMSE of 2 m3 ha-1 yr-1 and 1.7 kgC m-2 respectively – with inventory-derived estimates at country level for 20 European countries. Our simulations estimate a mean European forest NEP of 175 ± 52 gC m-2 yr-1 in the 1990s. The model simulation that is most consistent with inventory records provides an upwards trend of forest NEP of 1 ± 0.5 gC m-2 yr-2 between 1950 and 2000 across the EU 25. Further, the method used for reconstructing past age structure was found to dominate its contribution to temporal trends in NEP. The potentially large fertilizing effect of nitrogen deposition cannot be told apart as the model does not explicitly simulate the nitrogen cycle. Among the three drivers that were considered in this study, the fertilizing effect of increasing [CO2] explains about 61% of the simulated trend, against 26% to changes in climate, and 13% only to changes in forest age structure. The major role of [CO2] at the continental scale is due to its homogeneous impact on NPP. At the local scale, however, changes in climate and forest age structure often dominate trends in NEP by affecting NPP and heterotrophic respiration.

Description: Temporal trends of N 2 O fluxes across the soil-atmosphere interface were determined using continuous flux chamber measurements over an entire growing season of a subsurface aerating macrophyte ( P halaris arundinacea ) in a non-managed Danish wetland. Observed N 2 O fluxes were linked to changes in subsurface N 2 O and O 2 concentrations, water level, light intensity as well as mineral-N availability. Weekly concentration profiles showed that seasonal variations in N 2 O concentrations were directly linked to the position of the WL and O 2 availability at the capillary fringe above the WL. N 2 O flux measurements showed surprisingly high temporal variability with marked changes in fluxes and shifts in flux directions from net source to net sink within hours associated with changing light conditions. Systematic diurnal shifts between net N 2 O emission during day time and deposition during night time were observed when max subsurface N 2 O concentrations were located below the root zone. Correlation (p〈0.001) between diurnal variations in O 2 concentrations and incoming PAR radiation highlighted the importance of plant-driven subsoil aeration of thse root zone and the associated controls on coupled nitrification/denitrification. Therefore, P . arundinacea played an important role in facilitating N 2 O transport from the root zone to the atmosphere and exclusion of the aboveground biomass in flux chamber measurements may lead to significant underestimations on net ecosystem N 2 O emissions. Complex interactions between seasonal changes in O 2 and mineral N-availability following near-surface WL fluctuations in combination with plant mediated gas transport by P . arundinacea controlled the subsurface N 2 O concentrations and gas transport mechanisms responsible for N 2 O fluxes across the soil-atmosphere interface. Results demonstrate the necessity for addressing this high temporal variability and potential plant transport of N 2 O in future studies of net N 2 O exchange across the soil-atmosphere interface

Description: Although the effects of atmospheric nitrogen deposition on species composition are relatively well known, the roles of the different forms of nitrogen, in particular gaseous ammonia (NH 3 ), have not been tested in the field. Since 2002, we have manipulated the form of N deposition to an ombrotrophic bog, Whim, on deep peat in southern Scotland, with low ambient N (wet + dry = 8 kg N ha −1 y −1 ) and S (4 kg S ha −1 y −1 ) deposition. A gradient of ammonia (NH 3 , dry N), from 70 kg N ha −1 y −1 down to background, 3-4 kg N ha −1 y −1 was generated by free air release. Wet ammonium (NH 4 + , wet N) was provided to replicate plots in a fine rainwater spray (NH 4 Cl at +8, +24, +56 kg N ha −1 y −1 ). Automated treatments are coupled to meteorological conditions, in a globally unique, field experiment. Ammonia concentrations were converted to NH 3 -N deposition (kg N ha −1 ) using a site / vegetation specific parameterization. Within 3 years, exposure to relatively modest deposition of NH 3 , 20-56 kg NH 3 -N ha −1 y −1 led to dramatic reductions in species cover, with almost total loss of Calluna vulgaris , Sphagnum capillifolium and Cladonia portentosa . These effects appear to result from direct foliar uptake and interaction with abiotic and biotic stresses, rather than via effects on the soil. Additional wet N by contrast, significantly increased Calluna cover after 5 years at the 56 kg N dose, but reduced cover of Sphagnum and Cladonia . Cover reductions caused by wet N were significantly different from and much smaller than those caused by equivalent dry N doses. The effects of gaseous NH 3 described here, highlight the potential for ammonia to destroy acid heathland and peat bog ecosystems. Separating the effects of gaseous ammonia and wet ammonium deposition, for a peat bog, have significant implications for regulatory bodies and conservation agencies.

Description: Many factors contribute to the non-random processes of extinctions and invasions that are changing the structure of ecological communities worldwide. These factors include the attributes of the species, their abiotic environment, and the interactions and feedbacks between them. The relative importance of these factors has been difficult to quantify. We used nested subset theory and a novel permutation-based extension of gradient analysis to disentangle the direct and indirect pathways by which these factors affect the metacommunity structure of freshwater fishes inhabiting the streams tributary to the San Francisco Bay. Our analyses provide quantitative measures of how species and stream attributes may influence extinction vulnerability and invasion risk, highlight the need for considering the multiple interacting drivers of community change concurrently, and indicate that the ongoing disassembly and assembly of Bay Area freshwater fish communities are not fully symmetric processes. Fish communities are being taken apart and put back together in only partially analogous trajectories of extinction and invasion for which no single explanatory hypothesis is sufficient. Our study thereby contributes to the forecasting of continued community change and its effects on the functioning of freshwater ecosystems.

Description: Climate change is likely to have major impacts on the distribution of planted and natural forests. Here we demonstrate how a process-based niche model (CLIMEX) can be extended to project globally the potential habitat suitable for Douglas-fir. Within this distribution we use CLIMEX to predict abundance of the pathogen P haeocryptopus gaeumannii and severity of its associated foliage disease, Swiss needle cast. The distribution and severity of the disease, which can strongly reduce growth rate of Douglas-fir, is closely correlated with seasonal temperatures and precipitation. This model is used to project how climate change during the 2080s may alter the area suitable for Douglas-fir plantations within New Zealand. The climate change scenarios used indicate that the land area suitable for Douglas-fir production in the North Island will be reduced markedly from near 100% under current climate to 36 – 64% of the total land area by 2080's. Within areas shown to be suitable for the host in the North Island, four of the six climate change scenarios predict substantial increases in disease severity that will make these regions at best marginal for Douglas-fir by the 2080's. In contrast, most regions in the South Island are projected to sustain relatively low levels of disease, and remain suitable for Douglas-fir under climate change over the course of this century.

Description: Soils are both a major source and sink of nitrous oxide (N 2 O), but the proportion of soil N 2 O production released to the atmosphere (termed the N 2 O yield) is poorly constrained due to the difficulty in measuring gross N 2 O production. The quantification of gross N 2 O fluxes would greatly improve our ability to predict N 2 O dynamics across the soil-atmosphere interface. We report a new approach, the 15 N 2 O pool dilution technique, to measure rates of gross N 2 O production and consumption under laboratory and field conditions. In the lab, gross N 2 O production and consumption compared well between the 15 N 2 O pool dilution and acetylene inhibition methods whereas the 15 NO 3 - tracer method measured significantly higher rates. In the field, N 2 O emissions were not significantly affected by increasing chamber headspace concentrations up to 100 ppb 15 N 2 O. The pool dilution model estimates of 14 N 2 O and 15 N 2 O concentrations as well as net N 2 O fluxes fit observed data very well, suggesting that the technique yielded robust estimates of gross N 2 O production. Estimated gross N 2 O consumption rates were underestimated relative to rates calculated as the difference between gross and net N 2 O production rates, possibly due to heterogeneous and/or inadequate tracer diffusion to deeper layers in the soil profile. Gross N 2 O production rates were high, averaging 8.4 ± 3.2 mg N m −2 d −1 , and were most strongly correlated to mineral nitrogen concentrations and denitrifying enzyme activity (R 2 = 0.73). Gross N 2 O production rates varied spatially, with the highest rates in soils with the best drainage and the highest mineral N availability. Estimated and calculated N 2 O consumption rates constrained the average N 2 O yield from 0.70 to 0.84. Our results demonstrate that the 15 N 2 O pool dilution technique can provide well-constrained estimates of N 2 O yields and field rates of gross N 2 O production correlated to soil characteristics, improving our understanding of terrestrial N 2 O dynamics.

Description: Over the next century, changes in the global climate are expected to have major consequences for plant communities, possibly including the exacerbation of species invasions. We evaluated this possibility in the grass flora of California, which is economically and ecologically important and heavily invaded. We used a novel, trait-based approach involving two components: identifying differences in trait composition between native and exotic components of the grass flora and evaluating contemporary trait-climate relationships across the state. The combination of trait-climate relationships and trait differences between groups allows us to predict changes in the exotic-native balance under climate change scenarios. Exotic species are more likely to be annual, taller, with larger leaves, larger seeds, higher specific leaf area and higher leaf N percentage than native species. Across the state, all of these traits are associated with regions with higher temperature. Therefore, we predict that increasing temperatures will favor trait states that tend to be possessed by exotic species, increasing the dominance of exotic species. This prediction is corroborated by the current distribution of exotic species richness relative to native richness in California; warmer areas contain higher proportions of exotic species. This pattern was very well captured by a simple model that predicts invasion severity given only the trait-climate relationship for native species and trait differences between native and exotic species. This study provides some of the first evidence for an important interaction between climate change and species invasions across very broad geographic and taxonomic scales.

Description: Substantial uncertainty surrounds how forest ecosystems will respond to the simultaneous impacts of multiple global change drivers. Long-term forest dynamics are sensitive to changes in tree mortality rates, however we lack an understanding of the relative importance of the factors that affect tree mortality across different spatial and temporal scales. We used the US Forest Service Forest Inventory and Analysis database to evaluate the drivers of tree mortality for eastern temperate forest at the individual-level across spatial scales from tree to landscape to region. We investigated thirteen covariates in four categories: climate, air pollutants, topography, and stand characteristics. Overall, we found that tree mortality was most sensitive to stand characteristics and air pollutants. Different functional groups also varied considerably in their sensitivity to environmental drivers. This research highlights the importance of considering the interactions among multiple global change agents in shaping forest ecosystems.

Description: It is not clear whether the consistent positive effect of elevated CO 2 on soil respiration (soil carbon flux, SCF) results from increased plant and microbial activity due to (1) greater C availability through CO 2 -induced increases in C inputs or (2) enhanced soil moisture via CO 2 -induced declines in stomatal conductance and plant water use. Global changes such as biodiversity loss or nitrogen (N) deposition may also affect these drivers, interacting with CO 2 to affect SCF. To determine the effects of these factors on SCF and elucidate the mechanism(s) behind the effect of elevated CO 2 on SCF, we measured SCF and soil moisture throughout a growing season in the Biodiversity, CO 2 , and N (BioCON) experiment. Increasing diversity and N caused small declines in soil moisture. Diversity had inconsistent small effects on SCF through its effects on abiotic conditions, while N had a small positive effect that was unrelated to soil moisture. Elevated CO 2 had large consistent effects, increasing soil moisture by 26% and SCF by 45%. However, CO 2 -induced changes in soil moisture were weak drivers of SCF: CO 2 effects on SCF and soil moisture were uncorrelated, CO 2 effect size did not change with soil moisture, within-day CO 2 effects via soil moisture were neutral or weakly negative, and the estimated effect of increased C availability was 14 times larger than that of increased soil moisture. Combined with previous BioCON results indicating elevated CO 2 increases C availability to plants and microbes, our results suggest increased SCF is driven by CO 2 -induced increases in substrate availability. Our results provide further support for increased rates of belowground C cycling at elevated CO 2 and evidence that, unlike the response of productivity to elevated CO 2 in BioCON, the response of SCF is not strongly N limited. Thus, N limited grasslands are unlikely to act as a C sink under elevated CO 2 .

Description: Quantification of rhizodeposition (root exudates and root turnover) represents a major challenge for understanding the links between above-ground assimilation and below-ground anoxic decomposition of organic carbon in rice paddy ecosystems. Free-air CO 2 enrichment (FACE) fumigating depleted 13 CO 2 in a rice paddy resulted in a smaller 13 C/ 12 C ratio in plant assimilated carbon, providing a unique measure by which we partitioned the sources of decomposed gases (CO 2 and CH 4 ) into current-season photosynthates (new C) and soil organic matter (old C). Additionally, we imposed a soil warming treatment nested within the CO 2 treatments to assess whether the carbon source was sensitive to warming. Compared with the ambient CO 2 treatment, the FACE treatment decreased the 13 C/ 12 C ratio not only in the rice-plant carbon but also in the soil CO 2 and CH 4 . The estimated new C contribution to dissolved CO 2 was minor (~20%) at the tillering stage, increased with rice growth and was about 50% from the panicle formation stage onwards. For CH4, the contribution of new C was greater than for heterotrophic CO2 production; approximately 40–60% of season-total CH 4 production originated from new C with a tendency toward even larger new C contribution with soil warming, presumably because enhanced root decay provided substrates for greater CH 4 production. The results suggest a fast and close coupling between photosynthesis and anoxic decomposition in soil, and further indicate a positive feedback of global warming by enhanced CH 4 emission through greater rhizodeposition.

Description: ABSTRACT Daily minimum temperature (T min ) has increased faster than daily maximum temperature (T max ) in many parts of the world, leading to decreases in diurnal temperature range (DTR). Projections suggest these trends are likely to continue in many regions, particularly northern latitudes and in arid regions. Despite wide speculation that asymmetric warming has different impacts on plant and ecosystem production than equal-night-and-day warming, there has been little direct comparison of these scenarios. Reduced DTR has also been widely misinterpreted as a result of night-only warming, when in fact T min occurs near dawn, indicating higher morning as well as night temperatures. We report on the first experiment to examine ecosystem-scale impacts of faster increases in T min than T max, using precise temperature controls to create realistic diurnal temperature profiles with gradual day-night temperature transitions and elevated early morning as well as night temperatures. Studying a constructed grassland ecosystem containing species native to Oregon, USA, we found the ecosystem lost more carbon at elevated than ambient temperatures, but was unaffected by the 3°C difference in DTR between symmetric warming (constantly ambient +3.5°C) and asymmetric warming (dawn T min =ambient +5°C, afternoon T max = ambient +2°C). Reducing DTR had no apparent effect on photosynthesis, likely because temperatures were most different in the morning and late afternoon when light was low. Respiration was also similar in both warming treatments, because respiration temperature sensitivity was not sufficient to respond to the limited temperature differences between asymmetric and symmetric warming. We concluded that changes in daily mean temperatures, rather than changes in T min /T max , were sufficient for predicting ecosystem carbon fluxes in this reconstructed Mediterranean grassland system.

Description: The long-term effects of conservation management practices on greenhouse gas fluxes from tropical/subtropical croplands remain to be uncertain. Using both manual and automatic sampling chambers, we measured N 2 O and CH 4 fluxes at a long-term experimental site (1968-present) in Queensland, Australia from 2006 to 2009. Annual net greenhouse gas fluxes (NGGF) were calculated from the 3-year mean N 2 O and CH 4 fluxes and the long-term soil organic carbon changes. N 2 O emissions exhibited clear daily, seasonal and interannual variations, highlighting the importance of whole-year measurement over multiple years for obtaining temporally representative annual emissions. Averaged over 3 years, annual N 2 O emissions from the unfertilised and fertilised soils (90 kg N ha −1  yr −1 as urea) amounted to 138 g N ha −1 and 902 g N ha −1 , respectively. The average annual N 2 O emissions from the fertilised soil were 388 g N ha −1 lower under no-till (NT) than under conventional tillage (CT) and 259 g N ha −1 higher under stubble retention (SR) than under stubble burning (SB). Annual N 2 O emissions from the unfertilised soil were similar between the contrasting tillage and stubble management practices. The average emission factors of fertiliser N were 0.91%, 1.20%, 0.52% and 0.77% for the CT-SB, CT-SR, NT-SB and NT-SR treatments, respectively. Annual CH 4 fluxes from the soil were very small (−0.2 to 0.3 kg CH 4  ha −1  yr −1 ) with no significant difference between treatments. The NGGF were 277–350 kg CO 2 -e ha −1  yr −1 for the unfertilised treatments and 401–710 kg CO 2 -e ha −1  yr −1 for the fertilised treatments. Among the fertilised treatments, N 2 O emissions accounted for 52–97% of NGGF and NT-SR resulted in the lowest NGGF (401 kg CO 2 -e ha −1  yr −1 or 140 kg CO 2 -e t −1 grain). Therefore, NT-SR with improved N fertiliser management practices was considered the most promising management regime for simultaneously achieving maximal yield and minimal NGGF.

Description: Understanding how net ecosystem exchange (NEE) changes with temperature is central to the debate on climate change-carbon cycle feedbacks, but still remains unclear. Here we used eddy covariance measurements of NEE from 20 FLUXNET sites (203 site-years of data) in mid- and high latitude forests to investigate the temperature response of NEE. Years were divided into two half thermal years (increasing temperature in spring and decreasing temperature in autumn) using the maximum daily mean temperature. We observed a parabolic-like pattern of NEE in response to temperature change in both the spring and autumn half thermal years. However, at similar temperatures, NEE was considerably depressed during the decreasing temperature season as compared to the increasing temperature season, inducing a counter-clockwise hysteresis pattern in the NEE - temperature relation at most sites. The magnitude of this hysteresis was attributable mostly (68%) to gross primary production (GPP) differences but little (8%) to ecosystem respiration (ER) differences between the two half thermal years. The main environmental factors contributing to the hysteresis responses of NEE and GPP were daily accumulated radiation. Soil water content (SWC) also contributed to the hysteresis response of GPP but only at some sites. Shorter day length, lower light intensity, lower SWC and reduced photosynthetic capacity may all have contributed to the depressed GPP and net carbon uptake during the decreasing temperature seasons. The resultant hysteresis loop is an important indicator of the existence of limiting factors. As such, the role of radiation, LAI and SWC should be considered when modeling the dynamics of carbon cycling in response to temperature change.

Description: We evaluated above and below ground ecosystem changes in a 16 year, combined fertilization and warming experiment in a High Arctic tundra deciduous shrub heath (Alexandra Fiord, Ellesmere Island, NU, Canada). Soil emissions of the three key greenhouse gases (carbon dioxide, methane, and nitrous oxide) were measured in mid July 2009 using soil respiration chambers attached to a FTIR system. Soil chemical and biochemical properties including Q 10 values for CO 2 , CH 4 , and N 2 O, Bacteria and Archaea assemblage composition, and the diversity and prevalence of key nitrogen cycling genes including bacterial amoA , crenarchaeal amoA , and nosZ were measured. Warming and fertilization caused strong increases in plant community cover and height but had limited effects on greenhouse gas fluxes and no substantial effect on soil chemistry or biochemistry. Similarly, there was a surprising lack of directional shifts in the soil microbial community as a whole or any change at all in microbial functional groups associated with CH 4 consumption or N 2 O cycling in any treatment. Thus, it appears that while warming and increased nutrient availability have strongly affected the plant community over the last 16 years, the below ground ecosystem has not yet responded. This resistance of the soil ecosystem has resulted in limited changes in greenhouse gas fluxes in response to the experimental treatments.

Description: Global climate change affects ecosystems via several trophic levels. We investigated changes in the timing of breeding in the willow tit ( Poecile montanus ) and timing of its caterpillar food resource in relation to warming springs in a boreal forest. We used generalized linear mixed effect models to study the importance of synchrony between the timing of breeding in willow tits and the caterpillar food availability on the breeding success, measured as nestling survival rate and mean nestling weight. Both the timing of breeding and the timing of the caterpillar peak advanced during the last decades, and were well explained by spring temperatures. Unlike in most passerine populations studied, synchrony has improved with rising spring temperatures. However, it had only a modest although statistically significant positive influence on breeding success. Spring temperatures do not seem to be used as cues for the timing of caterpillar food availability by willow tits. We conclude that responses to climatic warming seem to be population, species and habitat specific, necessitating research in a wide range of taxa in different climatic zones.

Description: Although atmospheric nitrogen (N) deposition and climate changes are both recognized as major components of global change, their interaction at ecosystem level is less well understood. A stratified resampling approach was used to investigate the potential impact of changing levels of atmospheric nitrogen deposition and climate change on species composition of nutrient-poor acid grasslands within the French Atlantic Domain (FAD). The study was based on a comparison, over a period of 25 years, of 162 past and present vegetation records assigned to the species-rich Nardus grasslands and distributed in regional community types (CTs). Similarly, the characterisation of N deposition and climate was stratified according to (1) past (1980-1990) and present (1995-2005) periods; (2) FAD and CT scales. Despite the relatively short time span between sampling periods, significant N deposition and climate changes were detected as well as vegetation changes. Correspondence analysis showed that the relative importance of N deposition and climate in explaining vegetation changes depended on the spatial scale of investigation (FAD vs . local CTs) and the CT. At the FAD scale, the increase of annual mean temperature and decrease of water availability were clearly related to changes in floristic composition. At the local scale, the most stable CT experienced no significant climate change and a stable load of N deposition whereas the CTs characterised by the largest floristic changes were associated with dramatic climate changes and moderate loads in both oxidized and reduced N deposition. Despite the narrow gradient of deposition investigated, N deposition was related to significant grassland community changes, depending on the region i.e . climate context and on whether N deposition was in the oxidized or reduced form. Our results suggest that N deposition drives grassland composition at the local scale, in interaction with climate, while climate changes remain the predominant driver at the FAD scale.

Description: During the last decades human activity has altered the natural cycle of nitrogen and phosphorus on a global scale, producing significant emissions to waters. In Europe, the amount of nutrients discharged from rivers to coastal waters as well as the effects of mitigation measures in place are known only partially, with no consistent temporal and spatial cover. In this study we quantify the loads and concentration of nitrogen and phosphorus discharged in the European seas over the period 1985-2005, and we discuss their impact on coastal ecosystems. To support our analysis, a catchment database covering the whole of Europe was developed together with data layers of nutrients diffuse and point sources, and the statistical model GREEN was used to estimate the annual loads of nitrogen and phosphorus discharged in all European seas. The results of this study show that during the last 20 years, Europe has discharged 4.1-4.8 Tg/yr of nitrogen and 0.2-0.3 Tg/yr of phosphorus to its coastal waters. We show that beside the North Sea and part of the Baltic Sea, annual nutrient exports have not changed significantly, in spite of the implementation of measures to reduce nutrient sources, and that the N:P ratio has increased steadily, especially in the North, Mediterranean and Atlantic seas. The response of river basins to changes in inputs was not linear, but influenced by climatic variations and nutrients previously accumulated in soils and aquifers. An analysis of the effects of European environmental policies shows that measures to reduce phosphorus were more successful that those tackling nitrogen and that policies aimed at point sources were more effective or more effectively implemented than those controlling pollution from diffuse sources. The increase of the N:P ratio could fuel eutrophication in N-limited coastal ecosystems, reducing biodiversity and the ecosystem's resilience to future additional anthropogenic stress, such as climate change.

Description: North American fire-adapted forests are experiencing changes in fire-frequency and climate. These novel conditions may alter post-wildfire responses of fire-adapted trees that survive fires, a topic that has received little attention. Historical, frequent, low intensity wildfire in many fire-adapted forests is generally thought to have a positive effect on the growth and vigor of trees that survive fires. Whether such positive effects can persist under current and future climate conditions is not known. Here, we evaluate long term responses to recurrent 20 th century fires in ponderosa pine, a fire-adapted tree species, in unlogged forests in north central Idaho. We also examine short-term responses to individual 20 th century fires and evaluate whether these responses have changed over time and whether potential variability relates to climate variables and time since last fire. Growth responses were assessed by comparing tree-ring measurements from trees in stands burned repeatedly during the 20 th century at roughly the historical fire-frequency with trees in paired control stands that had not burned for at least 70 years. Contrary to expectations, only one site showed significant increases in long-term growth responses in burned stands compared to control stands. Short-term responses showed a trend of increasing negative effects of wildfire (reduced diameter growth in the burned stand compared to the control stand) in recent years that had drier winters and springs. There was no effect of time since the previous fire on growth responses to fire. The possible relationship of novel climate conditions with negative tree growth responses in trees that survive fire are discussed. A trend of negative growth responses to wildfire in old-growth forests could have important ramifications for forest productivity and carbon-balance under future climate scenarios.

Description: Tree species are expected to track warming climate by shifting their ranges to higher latitudes or elevations, but current evidence of latitudinal range shifts for suites of species is largely indirect. In response to global warming, offspring of trees are predicted to have ranges extend beyond adults at leading edges and the opposite relationship at trailing edges. Large-scale forest inventory data provides an opportunity to compare present latitudes of seedlings and adult trees at their range limits. Using the USDA Forest Service's Forest Inventory and Analysis (FIA) data, we directly compared seedling and tree 5 th and 95 th percentile latitudes for 92 species in 30 longitudinal bands for 43,334 plots across the eastern U.S. We further compared these latitudes with 20 th century temperature and precipitation change and functional traits, including seed size and seed spread rate. Results suggest that 58.7% of the tree species examined show the pattern expected for a population undergoing range contraction, rather than expansion, at both northern and southern boundaries. Fewer species show a pattern consistent with a northward shift (20.7%) and fewer still with a southward shift (16.3%). Only 4.3% are consistent with expansion at both range limits. When compared with the 20 th century climate changes that have occurred at the range boundaries themselves, there is no consistent evidence that population spread is greatest in areas where climate has changed most; nor are patterns related to seed size or dispersal characteristics. The fact that the majority of seedling extreme latitudes are less than those for adult trees may emphasize the lack of evidence for climate-mediated migration, and should increase concerns for the risks posed by climate change.

Description: Coccolithophores are unicellular phytoplankton that produce calcium carbonate coccoliths as an exoskeleton. Emiliania huxleyi , the most abundant coccolithophore in the world's ocean, plays a major role in the global carbon cycle by regulating the exchange of CO 2 across the ocean-atmosphere interface through photosynthesis and calcium carbonate precipitation. As CO 2 concentration is rising in the atmosphere, the ocean is acidifying and ammonium (NH 4 + ) concentration of future ocean water is expected to rise. The latter is attributed to increasing anthropogenic nitrogen (N) deposition, increasing rates of cyanobacterial N 2 fixation due to warmer and more stratified oceans, and decreased rates of nitrification due to ocean acidification. Thus future global climate change will cause oceanic phytoplankton to experience changes in multiple environmental parameters including CO 2 , pH, temperature and nitrogen source. This study reports on the combined effect of elevated p CO 2 and increased NH 4 + to nitrate (NO 3 - ) ratio (NH 4 + /NO 3 - ) on E. huxleyi, maintained in continuous cultures for more than 200 generations under two p CO 2 levels and two different N sources. Here we show that NH 4 + assimilation under N-replete conditions depresses calcification at both low and high p CO 2 , alters coccolith morphology, and increases primary production. We observed that N source and p CO 2 synergistically drive growth rates, cell size and the ratio of inorganic to organic carbon. These responses to N source suggest that, compared to increasing CO 2 alone, a greater disruption of the organic carbon pump could be expected in response to the combined effect of increased NH 4 + /NO 3 - ratio and CO 2 level in the future acidified ocean. Additional experiments conducted under lower nutrient conditions are needed prior to extrapolating our findings to the global oceans. Nonetheless, our results emphasize the need to assess combined effects of multiple environmental parameters on phytoplankton biology in order to develop accurate predictions of phytoplankton responses to ocean acidification.

Description: A change in land use from agriculture to forest generally increases soil acidity. However, it remains unclear to what extent plant traits can enhance or mitigate soil acidification caused by atmospheric deposition. Soil acidification is detrimental for the survival of many species. An in-depth understanding of tree species-specific effects on soil acidification is crucial for soil protection, particularly in view of the predicted global increases in acidifying nitrogen (N) deposition. Here, we report soil acidification rates in a chronosequence of broadleaved deciduous forests planted on former arable land in Belgium. This region receives one of the highest loads of potentially acidifying atmospheric deposition in Europe, which allowed us to study a ‘worst case scenario’. We show that less than four decades of forest development caused significant soil acidification. Atmospheric deposition undoubtedly and unequivocally drives post-agricultural forests towards more acidic conditions, but the rate of soil acidification is also determined by the tree species-specific leaf litter quality and litter decomposition rates. We propose that the intrinsic differences in leaf litter quality among tree species create fundamentally different nutrient cycles within the ecosystem, both directly through the chemical composition of the litter and indirectly through its effects on the size and composition of earthworm communities. Poor leaf litter quality contributes to the absence of a burrowing earthworm community, which retards leaf litter decomposition and, consequently, results in forest-floor build-up and soil acidification. Also nutrient uptake and N 2 fixation are causing soil acidification, but were found to be less important. Our results highlight the fact that tree species-specific traits significantly influence the magnitude of human pollution-induced soil acidification.

Description: Little is known about the impact of changing temperature regimes on composition and diversity of cryptogam communities in the Arctic and Subarctic, despite the well-known importance of lichens and bryophytes to the functioning and climate feedbacks of northern ecosystems. We investigated changes in diversity and abundance of lichens and bryophytes within long-term (9 -16 yrs) warming experiments and along natural climatic gradients, ranging from Swedish subarctic birch forest and subarctic/subalpine tundra to Alaskan arctic tussock tundra. In both Sweden and Alaska, lichen diversity responded negatively to experimental warming (with the exception of a birch forest) and to higher temperatures along climatic gradients. Bryophytes were less sensitive to experimental warming than lichens, but depending on the length of the gradient, bryophyte diversity decreased both with increasing temperatures and at extremely low temperatures. Among bryophytes, Sphagnum mosses were particularly resistant to experimental warming in terms of both abundance and diversity. Temperature, on both continents, was the main driver of species composition within experiments and along gradients, with the exception of the Swedish subarctic birch forest where amount of litter constituted the best explanatory variable. In a warming experiment in moist acidic tussock tundra in Alaska, temperature together with soil ammonium availability were the most important factors influencing species composition. Overall, dwarf shrub abundance (deciduous and evergreen) was positively related to warming but so were the bryophytes Sphagnum girgensohnii , Hylocomium splendens and Pleurozium schreberi ; the majority of other cryptogams showed a negative relationship to warming. This unique combination of intercontinental comparison, natural gradient studies and experimental studies shows that cryptogam diversity and abundance, especially within lichens, is likely to decrease under arctic climate warming. Given the many ecosystem processes affected by cryptogams in high latitudes (e.g. carbon sequestration, N 2 -fixation, trophic interactions), these changes will have important feedback consequences for ecosystem functions and climate.

Description: Forest disturbances are major sources of carbon dioxide to the atmosphere, and therefore impact global climate. Biogeophysical attributes, such as surface albedo (reflectivity), further control the climate-regulating properties of forests. Using both tower-based and remotely-sensed data sets, we show that natural disturbances from wildfire, beetle outbreaks, and hurricane wind throw can significantly alter surface albedo, and the associated radiative forcing either offsets or enhances the CO 2 forcing caused by reducing ecosystem carbon sequestration over multiple years. In the examined cases, the radiative forcing from albedo change is on the same order of magnitude as the CO 2 forcing. The net radiative forcing resulting from these two factors leads to a local heating effect in a hurricane-damaged mangrove forest in the sub-tropics, and a cooling effect following wildfire and mountain pine beetle attack in boreal forests with winter snow. Although natural forest disturbances currently represent less than half of gross forest cover loss, that area will likely increase in the future under climate change, making it imperative to represent these processes accurately in global climate models.

Description: A method was developed to estimate carbon consumed during wildland fires in interior Alaska based on medium-spatial scale data (60 m cell size) generated on a daily basis. Carbon consumption estimates were developed for 41 fire events in the large fire year of 2004 and 34 fire events from the small fire years of 2006 to 2008. Total carbon consumed during the large fire year (2.72 x 10 6 ha burned) was 64.7 Tg C, and the average carbon consumption during the small fire years (0.09 x 10 6 ha burned) was 1.3 Tg C. Uncertainties for the annual carbon emissions ranged from 13 to 21%. Carbon consumed from burning of black spruce forests represented 76% of the total during large fire years and 57% during small fire years. This was the result of the widespread distribution of black spruce forests across the landscape and the deep burning of the surface organic layers common to these ecosystems. Average carbon consumed was 3.01 kg m −2 during the large fire year and 1.69 kg m −2 during the small fire years. Most of the carbon consumption was from burning of ground layer fuels (85% in the large fire year and 78% in small fire years). Most of the difference in average carbon consumption between large and small fire years was in the consumption of ground layer fuels (2.60 vs. 1.31 kg m −2 during large and small fire years, respectively). There was great variation in average fuel consumption between individual fire events (0.56 to 5.06 kg m −2 ) controlled by variations in fuel types and topography, timing of the fires during the fire season, and variations in fuel moisture at the time of burning.

Description: Because of the long residence time of carbon in forests and soils, the current state and future behavior of the terrestrial biosphere is influenced by past variability in climate and anthropogenic land use. Over the last half-millennium, European terrestrial ecosystems were affected by the cool temperatures of the Little Ice Age, rising CO 2 concentrations, and human induced deforestation and land abandonment. To quantify these effects, we used the LPJ dynamic vegetation model driven by reconstructed climate, land use, and CO 2 concentrations to evaluate the carbon cycle of Europe. Though land use change was the major control on the carbon inventory of Europe over the last 500 years, the current state of the terrestrial biosphere is largely controlled by land use change during the past century. Between 1500 and 2000, climate variability could have led to temporary sequestration events of up to 3 Pg, while increasing atmospheric CO 2 concentrations during the 20 th century led to an increase in carbon storage of up to 15 Pg in our simulations. Anthropogenic land use could have caused between 25 Pg of carbon emissions and 5 Pg of uptake over the same time period, depending on the historical and spatial pattern of past land use and the timing of the reversal from deforestation to afforestation during the last two centuries. None of the currently existing anthropogenic land use change datasets adequately capture the timing of the forest transition in most European countries as recorded in historical observations. Despite considerable uncertainty, our scenarios indicate that with limited management, extant European forests have the potential to absorb between 5 and 12 Pg of carbon at the present day.

Description: Hotter and drier conditions projected for the southwestern U.S. can have a large impact on the abundance and composition of long-lived desert plant species. We used long-term vegetation monitoring results from thirty-nine large plots across four protected sites in the Sonoran Desert region to determine how plant species have responded to past climate variability. This cross-site analysis identified the plant species and functional types susceptible to climate change, the magnitude of their responses, and potential climate thresholds. In the relatively mesic mesquite savanna communities, perennial grasses declined with a decrease in annual precipitation, cacti increased, and there was a reversal of the Prosopis velutina expansion experienced in the 20 th century in response to increasing mean annual temperature (MAT). In the more xeric Arizona Upland communities, the dominant leguminous tree, Cercidium microphyllum , declined on hillslopes, and the shrub Fouquieria splendens decreased, especially on south- and west-facing slopes in response to increasing MAT. In the most xeric shrublands, the codominant species Larrea tridentata and its hemiparasite Krameria grayi decreased with a decrease in cool season precipitation and increased aridity, respectively. This regional-scale assessment of plant species response to recent climate variability is critical for forecasting future shifts in plant community composition, structure, and productivity.

Description: Ecosystem respiration is a primary component of the carbon cycle and understanding the mechanisms that determine its temperature dependence will be important for predicting how rates of carbon sequestration might respond to global warming. We used a rare model system, comprising a network of geothermally heated streams ranging in temperature from 5 to 25 °C, to explore the nature of the relationship between respiration and temperature. Using this ‘natural experiment’, we tested whether the natal thermal regime of stream communities influenced the temperature dependence of respiration in the absence of other potentially confounding variables. An empirical survey of 13 streams across the thermal gradient revealed that the temperature dependence of whole-stream respiration was equivalent to the average activation energy of the respiratory complex (0.6 – 0.7 eV). This observation was also consistent for in-situ benthic respiration. Laboratory experiments, incubating biofilms from four streams across the thermal gradient at a range of temperatures, revealed that the activation energy and Q 10 of respiration was remarkably consistent across streams, despite marked differences in their thermal history and significant turnover in species composition. Furthermore, absolute rates of respiration at standardised temperature were also unrelated to ambient stream temperature, but strongly reflected differences in biofilm biomass. Together, our results suggest that the core biochemistry, which drives the kinetics of oxidative respiratory metabolism may be well conserved among diverse taxa and environments, and that the intrinsic sensitivity of respiration to temperature is not influenced by ambient environmental temperature (and thermal history).

Description: Plant growth responses to rising atmospheric CO 2 and O 3 vary among genotypes and between species, which could plausibly influence the strength of competitive interactions for soil N. Due to the size-symmetric nature of belowground competition, we reasoned that differential growth responses to CO 2 and O 3 should shift as juvenile individuals mature, thereby altering competitive hierarchies and forest composition. In a 12-year-long forest FACE experiment, we used tracer 15 N and whole-plant N content to assess belowground competitive interactions among five Populus tremuloides genotypes, between a single P. tremuloides genotype and Betula papryrifera , as well as between the same single P. tremuloides genotype and Acer saccharum . Under elevated CO 2, the amount of soil N and 15 N obtained by the P. tremuloides genotype common to each community was contingent on the nature of belowground competition. When this genotype competed with its congeners, it obtained equivalent amounts of soil N and tracer 15 N under ambient and elevated CO 2 ; however, its acquisition of soil N under elevated CO 2 increased by a significant margin when grown in competition with B. papyrifera (+30%) and A. saccharum (+60%). In contrast, elevated O 3 had no effect on soil N and 15 N acquisition by the P. tremuloides genotype common in each community, regardless of competitive interactions. Under elevated CO 2 , the rank order of N acquisition among P. tremuloides genotypes shifted over time, indicating that growth responses to CO 2 change during ontogeny; this was not the case under elevated O 3 . In the aspen-birch community, the competitive advantage elevated CO 2 initially conveyed on birch diminished over time, whereas maple was a poor competitor for soil N in all regards. The extent to which elevated CO 2 and O 3 will shape the genetic structure and composition of future forests is, in part, contingent on the time-dependent effects of belowground competition on plant growth response.

Description: Conversion of grasslands to woodlands may alter the sensitivity of CO 2 exchange of individual plants and entire ecosystems to air temperature and precipitation. We combined leaf-level gas exchange and ecosystem-level eddy covariance measurements to quantify the effects of plant temperature sensitivity to ecosystem temperature responses of a grassland and mesquite woodland across seasonal precipitation periods. In so doing, we were able to estimate the role of moisture availability on ecosystem temperature sensitivity under large-scale vegetative shifts. Optimum temperatures ( T opt ) for net photosynthetic assimilation ( A ) and net ecosystem productivity ( NEP ) were estimated from a function fitted to A and NEP plotted against air temperature. The convexities of these temperature responses were quantified by the range of temperatures over which a leaf or an ecosystem assimilated 50% of maximum NEP (Ω 50 ). Under dry pre- and post-monsoon conditions, leaf-level Ω 50 in C 3 shrubs were two-to-three times that of C 4 grasses, but under moist monsoon conditions, leaf-level Ω 50 was similar between growth forms. At the ecosystems-scale, grassland NEP was more sensitive to precipitation, as evidenced by a 104% increase in maximum NEP at monsoon onset, compared to a 57% increase in the woodland. Also, woodland NEP was greater across all temperatures experienced by both ecosystems in all seasons. By maintaining physiological function across a wider temperature range during water-limited periods, woody plants assimilated larger amounts of carbon. This higher carbon-assimilation capacity may have significant implications for ecosystem responses to projected climate change scenarios of higher temperatures and more variable precipitation, particularly as semiarid regions experience conversions from C 4 grasses to C 3 shrubs. As regional carbon models, CLM 4.0, are now able to incorporate functional type and photosynthetic pathway differences, this work highlights the need for a better integration of the interactive effects of growth form/functional type and photosynthetic pathway on water resource acquisition and temperature sensitivity.

Description: Current climatic trends involve both increasing temperatures and climatic variability, with extreme events becoming more frequent. Increasing concern on extreme climatic events has triggered research on vegetation shifts. However, evidences of vegetation shifts resulting from these events are still relatively rare. Empirical evidence supports the existence of stabilizing processes minimizing and counteracting the effects of these events, reinforcing community resilience. We propose a demographic framework to understand this inertia to change based on the balance between adult mortality induced by the event and enhanced recruitment or adult survival after the event. The stabilizing processes potentially contributing to this compensation include attenuation of the adult mortality caused by the event, due to site quality variability, to tolerance, phenotypic variability and plasticity at population level, and to facilitative interactions. Mortality compensation may also occur by increasing future survival due to beneficial effect on growth and survival of the new conditions derived from global warming and increased climatic variability, to lowered competition resulting from reduced density in affected stands, or to antagonistic release when pathogens or predators are vulnerable to the event or the ongoing climatic conditions. Finally, mortality compensation may appear by enhanced recruitment due to release of competition with established vegetation, for instance as a consequence of gap openings after event-caused mortality, or to the new conditions which may be more favorable for seedling establishment, or to enhanced mutualistic interactions (pollination, dispersal). There are important challenges imposed by the need of long-term studies, but a research agenda focused on potentially stabilizing processes is well suited to understand the variety of responses, including lack of sudden changes and community inertia that are frequently observed in vegetation under extreme events. This understanding is crucial for the establishment of sound management strategies and actions addressed to improve ecosystem resilience under climate change scenarios.

Description: Nearly 5000 chamber measurements of CH 4 flux were collated from 21 sites across the UK, covering a range of soil and vegetation types, to derive a parsimonious model that explains as much of the variability as possible, with the least input requirements. Mean fluxes ranged from -0.3 to 27.4 nmol CH 4 m −2 s −1 , with small emissions or low rates of net uptake in mineral soils (site means of -0.3 to 0.7 nmol m −2 s −1 ) and much larger emissions from organic soils (site means of -0.3 to 27.4 nmol m −2 s −1 ). Less than half of the observed variability in instantaneous fluxes could be explained by independent variables measured. The reasons for this include measurement error, stochastic processes and, probably most importantly, poor correspondence between the independent variables measured and the actual variables influencing the processes underlying methane production, transport and oxidation. When temporal variation was accounted for, and the fluxes averaged at larger spatial scales, simple models explained up to ~75% of the variance in CH 4 fluxes. Soil carbon, peat depth, soil moisture and pH together provided the best sub-set of explanatory variables. However, where plant species composition data were available, this provided the highest explanatory power. Linear and non-linear models generally fitted the data equally well, with the exception that soil moisture required a power transformation. To estimate the impact of changes in peatland water table on CH 4 emissions in the UK, an emission factor of +0.4 g CH 4 m −2 y −1 per cm increase in water table height was derived from the data.

Description: Models that couple habitat suitability with demographic processes offer a potentially improved approach for estimating spatial distributional shifts and extinction risk under climate change. Applying such an approach to five species of Australian plants with contrasting demographic traits, we show that: (i) predicted climate-driven changes in range area are sensitive to the underlying habitat model, regardless of whether demographic traits and their interaction with habitat patch configuration are modelled explicitly; and (ii) caution should be exercised when using predicted changes in total habitat suitability or geographic extent to infer extinction risk, because the relationship between these metrics is often weak. Measures of extinction risk, which quantify threats to population persistence, are particularly sensitive to life-history traits, such as recruitment response to fire, which explained approximately 60% of the deviance in expected minimum abundance. Dispersal dynamics and habitat patch structure have the strongest influence on the amount of movement of the trailing and leading edge of the range margin, explaining roughly 40% of modelled structural deviance. These results underscore the need to consider direct measures of extinction risk (population declines and other measures of stochastic viability), as well as measures of change in habitat area, when assessing climate change impacts on biodiversity. Furthermore, direct estimation of extinction risk incorporates important demographic and ecosystem processes, which potentially influence species’ vulnerability to extinction due to climate change.

Description: Decomposition of soil organic matter (SOM) is mediated by microbial extracellular hydrolytic enzymes (EHEs). Thus, given the large amount of carbon (C) stored as SOM, it is imperative to understand how microbial EHEs will respond to global change (and warming in particular) to better predict the links between SOM and the global C cycle. Here, we measured the Michaelis-Menten kinetics [maximal rate of velocity ( V max ) and half-saturation constant ( K m )] of five hydrolytic enzymes involved in SOM degradation (cellobiohydrolase, β-glucosidase, β-xylosidase, α-glucosidase, and N-acetyl-β- d -glucosaminidase) in five sites spanning a boreal forest to a tropical rainforest. We tested the specific hypothesis that enzymes from higher latitudes would show greater temperature sensitivities than those from lower latitudes. We then used our data to parameterize a mathematical model to test the relative roles of V max and K m temperature sensitivities in SOM decomposition. We found that both V max and K m were temperature sensitive, with Q 10 values ranging from 1.53 to 2.27 for V max and 0.90-1.57 for K m . The Q 10 values for the K m of the cellulose-degrading enzyme β-glucosidase showed a significant (P=0.004) negative relationship with mean annual temperature, indicating that enzymes from cooler climates can indeed be more sensitive to temperature. Our model showed that K m temperature sensitivity can offset SOM losses due to V max temperature sensitivity, but the offset depends on the size of the SOM pool and the magnitude of V max . Overall, our results suggest that there is local adaptation of microbial EHE kinetics to temperature and that this should be taken into account when making predictions about the responses of C cycling to global change.

Description: Many amphibian species are threatened with extinction by the emerging infectious disease, chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis . This unprecedented global crisis threatens to reduce the biodiversity of the entire amphibian class. The fungus invades the skin and impairs the uptake and retention of essential ions leading to cardiac arrest. Antimicrobial peptides (AMPs) secreted into the mucus of some amphibians are thought to be an important defense against chytridiomycosis. However, little is known about the quantities of AMPs secreted under natural conditions, whether they are sufficient to protect against this pathogen, and how they interact with commensal microbes. To understand how defensive peptides and skin microbes may interact, it is essential to know the precise quantities of AMPs present under natural conditions. Using matrix-assisted laser desorption time-of-flight (MALDI-TOF) mass spectrometry and growth inhibition assays, we show that northern leopard frogs ( Rana pipiens ) at rest constitutively release low amounts of AMPs that inhibit B. dendrobatidis in vitro, and AMP defenses are elevated following a simulated predator attack. Using a synthetic peptide analog of brevinin-1Pb as an external control, we quantified the amounts of four previously described AMPs (brevinin 1Pa, brevinin-1Pb, brevinin-1Pd, and ranatuerin-2P) at several time points after secretion. Once secreted onto the skin, the peptides are most active for fifteen minutes, and small quantities persist for at least two hours. Taken together, our data suggest that small amounts of AMPs are rapidly available and quite stable on the skin of R. pipiens . They are effective inhibitors of B. dendrobatidis at these low constitutive concentrations but degrade within two hours, protecting the integrity of the skin and commensal bacteria.

Description: Climate change is likely to affect plants in multiple ways, but predicting the consequences for habitat suitability requires a process-based understanding of the interactions. This is at odds with existing approaches that are mostly phenomenological and largely restricted to predicting the effects of changing temperature and rainfall on species distributions at a coarse spatial scale. We examine the multiple effects of climate change, including predicting the effects of altered flood regimes and land-use change, on the potential distribution of the invasive riparian species lippia ( Phyla canescens ) across a 26,000 km 2 catchment in eastern Australia. We determined habitat suitability for lippia by combining process-understanding of experts and an eco-physiological bioclimatic model within a Bayesian belief network. The bioclimatic model predicted substantial changes in habitat suitability by 2070 under both a wetter (Echam Mark 3) and drier (Hadley Centre Mark 2) climate change scenario, but only the more likely drier scenario reduced suitability in our test region. The area suitable for lippia was predicted to increase at least three-fold with increased flooding under a wet climate scenario, although this would be partially negated by land-use change to cultivation. The region would become unsuitable to lippia with reduced flooding under a drier scenario irrespective of land-use changes, although existing populations would persist if grazing persisted. Independent field validation verified model structure and parameterisation, and therefore the opinion of experts, but identified site-scale deficiencies in the available environmental data layers. Model predictions suggest adaptation options for managing lippia will be greatly reduced under a drying scenario, but identify potential restoration opportunities under either scenario. This work highlights the value of predictive models that incorporate process-understanding at sufficiently fine spatial resolution to capture the important processes underpinning habitat suitability.

Description: High productivity and waterlogged conditions make many freshwater wetlands significant carbon sinks. Most wetland carbon studies focus on boreal peatlands, however, with less attention paid to other climates and to the effects of hydrogeomorphic settings and the importance of wetland vegetation communities on carbon sequestration. This study compares six temperate wetland communities in Ohio that belong to two distinct hydrogeomorphic types: an isolated depressional wetland site connected to the groundwater table, and a riverine flow-through wetland site that receives water from an agricultural watershed. Three cores were extracted in each community and analyzed for total carbon content to determine the soil carbon pool. Sequestration rates were determined by radiometric dating with 137 Cs and 210 Pb on a set of composite cores extracted in each of the six communities. Cores were also extracted in uplands adjacent to the wetlands at each site. Wetland communities had accretion rates ranging from 3.0 to 6.2 mm yr −1 . The depressional wetland sites had higher (P〈0.001) organic content (146 ± 4.2 gC kg −1 ) and lower (P〈0.001) bulk density (0.55 ± 0.01 Mg m −3 ) than the riverine ones (50.1 ± 6.9 gC kg −1 and 0.74 ± 0.06 Mg m −3 ). The soil carbon was 98-99% organic in the isolated depressional wetland communities and 85-98% organic in the riverine ones. The depressional wetland communities sequestered 317 ± 93 gC m −2 yr −1 , more (P〈0.01) than the riverine communities that sequestered 140 ± 16 gC m −2 yr −1 . The highest sequestration rate was found in the Quercus palustris forested wetland community (473 gC m −2 yr −1 ), while the one dominated by water lotus ( Nelumbo lutea ) was the most efficient of the riverine communities, sequestering 160 gC m −2 yr −1 . These differences in sequestration suggest the importance of addressing wetland types and communities in more detail when assessing the role of wetlands as carbon sequestering systems in global carbon budgets.

Description: Regime shifts are sudden changes in ecosystem structure that can be detected across several ecosystem components. The concept that regime shifts are common in marine ecosystems has gained popularity in recent years. Many studies have searched for the step-like changes in ecosystem state expected under a simple interpretation of this idea. However, other kinds of change, such as pervasive trends, have often been ignored. We assembled over 300 ecological time series from seven UK marine regions, covering two to three decades. We developed state-space models for the first principal component of the time series in each region, a common measure of ecosystem state. Our models allowed both trends and step changes, possibly in combination. We found trends in three out of seven regions, and step changes in two out of seven regions. Gradual as well as sudden changes are therefore important trajectories to consider in marine ecosystems.

Description: Many assessments of Product Carbon Footprint (PCF) for agricultural products omit emissions arising from land use change (LUC). In this study, we developed a framework based on IPCC national greenhouse gas inventory methodologies to assess the impacts of LUC from crop production using oil palm, soybean and oilseed rape as examples. Using ecological zone, climate and soil types from the top 20 producing countries, calculated emissions for transitions from natural vegetation to cropland on mineral soils under typical management ranged from –4.5 to 29.4 t CO 2 -eq ha −1 yr −1 over 20 years for oil palm and 1.2-47.5 t CO 2 -eq ha −1 yr −1 over 20 years for soybeans. Oilseed rape showed similar results to soybeans, but with lower maximum values because it is mainly grown in areas with lower C stocks. GHG emissions from other land use transitions were between 62 and 95% lower than those from natural vegetation for the arable crops, while conversions to oil palm were a sink for C. LUC emissions were considered on a national basis and also expressed per-tonne-of-oil-produced. Weighted global averages indicate that, depending on the land use transition, oil crop production on newly converted land contributes between –3.1 and 7.0 t CO 2 -eq t oil production −1 yr −1 for palm oil, 11.9-50.4 t CO 2 -eq t oil production −1 yr −1 for soybean oil, and 7.7-31.4 t CO 2 -eq t oil production −1 yr −1 for rapeseed oil. Assumptions made about crop and LUC distribution within countries contributed up to 66% error around the global averages for natural vegetation conversions. Uncertainty around biomass and soil C stocks were also examined. Finer resolution data and information (particularly on land management and yield) could improve reliability of the estimates but the framework can be used in all global regions and represents an important step forward for including LUC emissions in PCFs.

Description: As Earth's atmosphere accumulates carbon dioxide (CO 2 ) and other greenhouse gases, Earth's climate is expected to warm and precipitation patterns will likely change. The manner in which terrestrial ecosystems respond to climatic changes will feed back to affect the rate of climate change. Here, we describe responses of an old-field herbaceous community to a factorial combination of four levels of warming (up to 4 °C) and three precipitation regimes (drought, ambient, and rain addition) over two years. Warming suppressed total production, shoot production, and species richness, but only in the drought treatment. Root production did not respond to warming, but drought stimulated growth of deeper (〉10cm) roots by 121% in one year. Warming and precipitation treatments both affected functional group composition, with C 4 grasses and other annual and biennial species entering the C 3 perennial-dominated community in ambient rainfall and rain addition treatments as well as in warmed treatments. Our results suggest that, in this mesic system, expected changes in temperature or large changes in precipitation alone can alter functional composition but have little effect on total herbaceous plant growth. However, drought limits the capacity of the entire system to withstand warming. The relative insensitivity of our study system to climate suggests that the herbaceous component of old-field communities will not dramatically increase production in response to warming or precipitation change, and so is unlikely to provide either substantial increases in forage production or a meaningful negative feedback to climate change later this century.

Description: Anthropogenic global climate change has already led to alterations in biodiversity patterns by directly and indirectly affecting species distributions. It has been suggested that poikilothermic animals, including reptiles, will be particularly affected by global change and large-scale reptile declines have already been observed. Currently, half of the world′s freshwater turtles and tortoises are considered threatened with extinction and climate change may exacerbate these declines. In this study, we assess how global chelonian species richness will change in the near future. We use species distribution models developed under current climate conditions for 78% of all extant species and project them onto different Intergovernmental Panel on Climate Change (IPCC) climate change scenarios for 2080. We detect a strong dependence of temperature shaping most species ranges, which coincide with their general temperature related physiological traits (i.e. temperature dependent sex determination). Furthermore, the extent and distribution of the current bioclimatic niches of most chelonians may change remarkably in the near future, likely leading to a substantial decrease of local species abundance and ultimately a reduction in species richness. Future climatic changes may cause the ranges of 86% of the species to contract and of these ranges nearly 12% are predicted to be situated completely outside their currently realized niches. Hence, the interplay of increasing habitat fragmentation and loss due to climatic stress may result in a serious threat for several chelonian species.

Description: Erosion influences the lateral and vertical distribution of soil in agricultural landscapes. A better understanding of the effects of erosion and redistribution on soil organic carbon (C) within croplands would improve our knowledge of how management practices may affect global C dynamics. In this study the vertical and lateral distribution of soil organic C was characterized to evaluate the amounts and timescales of soil organic C movement, deposition and burial over the last 50 yr in different agroecosystems across Canada. There was strong evidence that a substantial portion of eroded sediment and soil organic C was deposited as colluvium close to its source area, thereby burying the original topsoil. The deepest aggraded profile was in a potato field and contained over 70 cm of deposited soil indicating an accumulation rate of 152 Mg ha yr −1 ; aggraded profiles in other sites had soil deposition rates of 40 to 90 Mg ha −1 yr −1 . The largest stock of soil organic C was 463 Mg ha −1 (to 50 cm depth) and soil C deposition ranged from about 2 to 4 Mg ha −1 yr −1 across all sites. A distinct feature observed in the aggraded profiles at every site was the presence of a large increase in soil organic C concentration near the bottom of the A horizon; the concentration of this C was greater than that at the soil surface. Compared to aggraded profiles the SOC concentration in eroded profiles did not differ with depth, suggesting that dynamic replacement of soil organic C had occurred in eroded soils. A large amount of soil organic C is buried in depositional areas of Canadian croplands; mineralization of this stock of C appears to have been constrained since burial, but it may be vulnerable to future loss by management practices, land use change and a warming climate.

Description: Experimental study of the effects of projected climate change on plant phenology allows us to isolate effects of warming on life history events such as leaf out. We simulated a 2°C temperature increase and 20% precipitation increase in a recently harvested temperate deciduous forest community in central Pennsylvania, USA, and observed the leaf out phenology of all species in 2009 and 2010. Over 130 plant species were monitored weekly in study plots, but due to high variability in species composition among plots, species were grouped into five functional groups: short forbs, tall forbs, shrubs, small trees, and large trees. Tall forbs and large trees, which usually emerge in the late spring, advanced leaf out 14-18 days in response to warming. Short forbs, shrubs, and small trees emerge early in spring and did not alter their phenology in response to warming or increased precipitation treatments. Earlier leaf out of tall forbs and large trees coincided with almost three weeks of increased community-level leaf area index (LAI), indicating greater competition and a condensed spring green-up period. While phenology of large trees and tall forbs appears to be strongly influenced by temperature-based growth cues, our results suggest that photoperiod and chilling cues more strongly influence the leaf out of other functional groups. Reduced freeze events and warmer temperatures from predicted climate change will interact with non-temperature growth cues to have cascading consequences throughout the ecosystem.

Description: Forest soils demonstrate in a microcosm the difficulties that are faced in quantifying methyl halide budgets. Carbon isotopic analyses have been proposed as a potential tool to address these concerns and in this study we have measured significant enrichment of the methyl chloride 13 C/ 12 C isotopic ratio (from -40.2±0.8‰ to -33.4±7.4‰) after nine minutes chamber emplacement on local Irish forest soils. This enrichment occurred independent of direction of methyl chloride fluxes. Measurements from soil cores in a flow-through-system (FTS) are comparable to chamber-based isotopic measurements and indicate that methyl chloride produced abiotically from organic soil horizons has an isotopic 13 C signature of -53±49‰, significantly less depleted than previously reported. Average net methyl chloride, methyl bromide and methyl iodide fluxes from soils (77.8±2.1, 1.25±3.63 and 0.35±2.00 μg MeX m −2 day −1 respectively) are in line with previously reported values; however, a better understanding of spatial and temporal variability is needed for budget quantification. Methyl halide fluxes from FTS soil cores demonstrate that, on a per gram basis, most consumption occurs through biologically driven processes in the O horizon, with progressively smaller contributions in deeper horizons. Sporadic biogenic production was observed in shallow soil horizons only. Abiotic production was at most 1/10 th the net biological reaction rate in the O-horizon and did not appear to be significantly different from zero in lower horizons. Modelled emissions based upon observed and reported rates for production, consumption and diffusion within the soil-atmosphere system are unable to replicate all observed isotopic signatures from chamber fluxes.

Description: Species are predicted to respond to global warming through “cold-ward” shifts in their geographic distributions due to encroachment into newly suitable habitats and/or dieback in areas that become climatically unsuitable. I conduct one of the first ever tests of this hypothesis for tropical plant species. I test for changes in the thermal distributions of 239 South American tropical plant species using dated herbarium records for specimens collected between 1970 and 2009. Supporting a priori predictions, many species (59%) exhibit some evidence of significant cold-ward range shifts even after correcting for collection biases. Over 1/3 of species (35%) show significant cold-ward movement in their hot thermal limits (mean rate of change = 0.022°C yr −1 ). Most of these species (85%; 30% of all study species) show no corresponding shift in their cold thermal limits. These unbalanced changes in the species’ thermal range limits may indicate species that are experiencing dieback due to their intolerance of rising temperatures coupled with an inability to expand into newly climatically-suitable habitats. On the other hand, 25% of species show significant cold-ward shifts in their cold thermal range limits (mean rate of change = 0.003°C yr −1 ), but 80% of these species (20% of all study species) show no corresponding shift in their hot thermal range limits. In these cases, the unbalanced shifts may indicate species that are able to “benefit” under global warming, at least temporally, by both tolerating rising temperatures and expanding into new suitable habitat. An important ancillary result of this study is that the number of species exhibiting significant range shifts was greatly influenced by shifting collector biases. This highlights the need to account for biases when analyzing natural history records or other long-term records.

Description: Recent reviews indicate that N deposition increases soil organic matter (SOM) storage in forests but the underlying processes are poorly understood. Our aim was to quantify the impacts of increased N inputs on soil C fluxes such as C mineralization and leaching of dissolved organic carbon (DOC) from different litter materials and native SOM. We added 5.5 g N m -2 y -1 as NH 4 NO 3 over one year to two beech forest stands on calcareous soils in the Swiss Jura. We replaced the native litter layer with 13 C-depleted twigs and leaves (δ 13 C:-38.4 and -40.8‰) in late fall and measured N effects on litter- and SOM-derived C fluxes. Nitrogen addition did not significantly affect annual C losses through mineralization, but altered the temporal dynamics in litter mineralization: increased N inputs stimulated initial mineralization during winter (leaves: +25%; twigs: +22%), but suppressed rates in the subsequent summer. The switch from a positive to a negative response occurred earlier and more strongly for leaves than for twigs (-21% vs. 0%). Nitrogen addition did not influence microbial respiration from the non-labeled calcareous mineral soil below the litter which contrasts with recent meta-analysis primarily based on acidic soils. Leaching of DOC from the litter layer was not affected by NH 4 NO 3 additions, but DOC fluxes from the mineral soils at 5 and 10 cm depth were significantly reduced by 17%. The 13 C tracking indicated that litter-derived C contributed less than 15% of the DOC flux from the mineral soil, with N additions not affecting this fraction. Hence, the suppressed DOC fluxes from the mineral soil at higher N inputs can be attributed to reduced mobilization of non-litter derived ‘older’ DOC. We relate this decline to an altered solute chemistry by NH4NO3 additions, an increased ionic strength and acidification resulting from nitrification, rather than to a change in microbial decomposition.

Description: Net ecosystem carbon dioxide (CO 2 ) productivity (NEP) was measured on shortgrass steppe (SGS) vegetation at the USDA Central Plains Experimental Range in northeastern Colorado from 2001 to 2003. Large year-to-year differences were observed in annual NEP, with 〉 95% of the net carbon uptake occurring during May and June. Low precipitation during the 2002 April to June time period greatly reduced annual net carbon uptake. Large precipitation events (〉 10 mm day −1 ) promoted carbon uptake, while small precipitation events (〈 10 mm day −1 ) enhanced heterotrophic respiration and resulted in a net loss of carbon from the system. Large precipitation event enhanced carbon uptake was attributed to increased soil water content (SWC), which promotes plant photosynthesis. The large precipitation events which occurred from July to October have lower increases in daytime net CO 2 uptake (NEP d ) due to the presence of low live plant biomass compared to earlier in the growing season. Live aboveground plant biomass (AGB), solar radiation, and SWC were the major variables that controlled NEP d , while AGB, SWC, and relative humidity control nighttime respiration losses (NEP n ). Aboveground plant biomass is the most important variable for controlling both NEP d and NEP n dynamics. These results suggest that the major factor controlling growing season NEP n is the amount of carbon fixed via photosynthesis during the day. Heterotrophic soil respiration is greatly enhanced for one to two days following rainfall events with daily rainfall events 〉 5 mm having a similar increase in respiration (〉 3.00 g m Cm −2 d −1 ). In addition, the size of the heterotrophic respiration pulse is independent of both the amount of time since the last rainfall event and the time of occurrence during the growing season.

Description: Isoprene is emitted from many terrestrial plants at high rates, accounting for an estimated 1/3 of annual global volatile organic compound emissions from all anthropogenic and biogenic sources combined. Through rapid photooxidation reactions in the atmosphere, isoprene is converted to a variety of oxidized hydrocarbons, providing higher-order reactants for the production of organic nitrates and tropospheric ozone, reducing the availability of oxidants for the breakdown of radiatively-active trace gases such as methane, and potentially producing hygroscopic particles that act as effective cloud condensation nuclei. However, the functional basis for plant production of isoprene remains elusive. It has been hypothesized that in the cell isoprene mitigates oxidative damage during the stress-induced accumulation of reactive oxygen species (ROS), but the products of isoprene-ROS reactions in plants have not been detected. Using pyruvate-2- 13 C leaf and branch feeding and individual branch and whole mesocosm flux studies, we present evidence that isoprene ( i ) is oxidized to methyl vinyl ketone and methacrolein ( i ox ) in leaves and that i ox /i emission ratios increase with temperature, possibly due to an increase in ROS production under high temperature and light stress. In a primary rainforest in Amazonia, we inferred significant in-plant isoprene oxidation (despite the strong masking effect of simultaneous atmospheric oxidation), from its influence on the vertical distribution of i ox uptake fluxes, which were shifted to low isoprene emitting regions of the canopy. These observations suggest that carbon investment in isoprene production is larger than that inferred from emissions alone and that models of tropospheric chemistry and biota-chemistry-climate interactions should incorporate isoprene oxidation within both the biosphere and the atmosphere with potential implications for better understanding both the oxidizing power of the troposphere and forest response to climate change.

Description: Aquatic biodiversity faces increasing threats from climate change, escalating exploitation of water, and land use intensification. Loss of vegetation in catchments (= watersheds) has been identified as a substantial problem for many river basins, and there is an urgent need to better understand how climate change may interact with changes in catchment vegetation to influence the ecological condition of freshwater ecosystems. We used 20 years of biological monitoring data from Victoria, southeastern Australia, to explore the influences of catchment vegetation and climate on stream macroinvertebrate assemblages. Southeastern Australia experienced a severe drought from 1997 to 2009, with reductions of stream flows 〉 50% in some areas. The prolonged drying substantially altered macroinvertebrate assemblages, with reduced prevalence of many flow-dependent taxa and increased prevalence of taxa that are tolerant of low-flow conditions and poor water quality. Stream condition, as assessed by several commonly used macroinvertebrate indices, was consistently better in reaches with extensive native tree cover in upstream catchments. Prolonged drought apparently caused similar absolute declines in macroinvertebrate condition indices regardless of vegetation cover, but streams with intact catchment and riparian vegetation started in better condition and remained so throughout the drought. The largest positive effects of catchment tree cover on both water quality and macroinvertebrate assemblages occurred above a threshold of ca 60% areal tree cover in upstream catchments and in higher rainfall areas. Riparian tree cover also had positive effects on macroinvertebrate assemblages, especially in warmer catchments. Our results suggest that the benefits of extensive tree cover via improved water quality and in-channel habitat persist during drought, and show the potential for vegetation management to reduce negative impacts of climatic extremes for aquatic ecosystems.

Description: Current climate change exacerbates the environmental restrictions on temperate species inhabiting low latitude edges of their geographical ranges. We examined how temperature variations due to current and future climate change are likely to affect populations’ persistence of stream-dwelling brown trout Salmo trutta at the vulnerable southern periphery of its range. Analysis of 33 years of air temperature data (1975-2007) by time-series models indicated a significant upward trend and a pronounced shift in air temperature around 1986-1987. This warming is associated with an ongoing population decline of brown trout, most likely caused by a loss of suitable thermal habitat in lower latitudes since the 1980s. Population decrease may not be attributed to physical habitat modification or angler pressure, since carrying capacity remained stable and populations were not overexploited. We developed regional temperature models, which predicted that unsuitable thermal habitat for brown trout increased by 93% when comparing climate conditions between 1975-1986 and 1993-2004. Predictions from climate envelope models showed that current climate change may be rendering unsuitable 12% of suitable thermal habitat each decade, resulting in an overall population decrease in the lower reaches of around 6% per year. Furthermore, brown trout catches markedly decreased 20% per year. Projections of thermal habitat loss under the ecologically friendly B2 SRES scenario showed that brown trout may lose half of their current suitable habitat within the study area by 2040 and become almost extinct by 2100. In parallel to the upstream movement of brown trout thermal habitat, warm water species are increasing their relative abundance in salmonid waters. Empirical evidence was provided of how current climate change threatens some of the most healthy native brown trout populations in Southern Europe and how forthcoming climate change is expected to further decrease the conservation status of the species.

Description: Ocean acidity has increased by 30% since preindustrial times due to the uptake of anthropogenic CO 2 and is projected to rise by another 120% before 2100 if CO 2 emissions continue at current rates. Ocean acidification is expected to have wide-ranging impacts on marine life, including reduced growth and net erosion of coral reefs. Our present understanding of the impacts of ocean acidification on marine life, however, relies heavily on results from short-term CO 2 perturbation studies. Here we present results from the first long-term CO 2 perturbation study on the dominant reef-building cold-water coral Lophelia pertusa and relate them to results from a short-term study to compare the effect of exposure time on the coral's responses. Short-term (one week) high CO 2 exposure resulted in a decline of calcification by 26-29% for a pH decrease of 0.1 units and net dissolution of calcium carbonate. In contrast, L. pertusa was capable to acclimate to acidified conditions in long-term (six months) incubations, leading to even slightly enhanced rates of calcification. Net growth is sustained even in waters sub-saturated with respect to aragonite. Acclimation to seawater acidification did not cause a measurable increase in metabolic rates. This is the first evidence of successful acclimation in a coral species to ocean acidification, emphasizing the general need for long-term incubations in ocean acidification research. To conclude on the sensitivity of cold-water coral reefs to future ocean acidification further ecophysiological studies are necessary which should also encompass the role of food availability and rising temperatures.

Description: Atmospheric nitrogen (N) deposition is a global and increasing threat to biodiversity and ecosystem function. Much of our current understanding of N deposition impacts comes from field manipulation studies, although interpretation may need caution where simulations of N deposition (in terms of dose, application rate and N form) have limited realism. Here we review responses to simulated N deposition from the UKREATE network, a group of nine experimental sites across the UK in a diversity of heathland, grassland, bog and dune ecosystems which include studies with a high level of realism and where many are also the longest running globally on their ecosystem type. Clear responses were seen across the sites with the greatest sensitivity shown in cover and species richness of bryophytes and lichens. Productivity was also increased at sites where N was the limiting nutrient, while flowering also showed high sensitivity, with increases and declines seen in dominant shrub and forb species, respectively. Critically, these parameters were responsive to some of the lowest additional loadings of N (7.7-10 kg ha −1 yr −1 ) showing potential for impacts by deposition rates seen in even remote and “unpolluted” regions of Europe. Other parameters were less sensitive, but nevertheless showed response to higher doses. These included increases in soil%N and ‘plant available’ KCl extractable N, N cycling rates and acid-base status. Furthermore, an analysis of accumulated dose that quantified response against the total N input over time suggested that N impacts can “build up” within an ecosystem such that even relatively low N deposition rates can result in ecological responses if continued for long enough. Given the responses have important implications for ecosystem structure, function, and recovery from N loading, the clear evidence for impacts at relatively low N deposition rates across a wide range of habitats is of considerable concern.

Description: Widespread drought-induced forest mortality has been documented across multiple tree species in North America in recent decades, but is a poorly understood component in terrestrial carbon (C) budgets. Recent severe drought in concert with elevated temperature likely triggered widespread forest mortality of trembling aspen ( Populus tremuloides ), the most widely distributed tree species in North America. The impact on the regional C budgets and spatial pattern of this drought-induced tree mortality, which has been termed “sudden aspen decline (SAD)”, is not well known and could contribute to increased regional C emissions, an amplifying feedback to climate change. We conducted a regional assessment of drought-induced live aboveground biomass (AGB) loss from SAD across 915 km 2 of southwestern Colorado, USA, and investigated the influence of topography on the severity of mortality by combining field measures, remotely sensed non-photosynthetically active vegetation and a digital elevation model. Mean (± standard deviation [sd]) remote sensing estimate of live AGB loss was 60.3 ± 37.3 Mg ha −1 , which was 30.7% of field measured AGB, totaling 2.7 Tg of potential C emissions from this dieback event. Aspen forest health could be generally categorized as healthy (0-30% field measured canopy dieback), intermediate (31-50%) and SAD (51-100%), with the remote sensing estimated mean (± sd) live AGB losses of 26.4 ± 15.1 Mg ha −1 , 64.5 ± 9.2 Mg ha −1 and 108.5 ± 24.0 Mg ha −1 , respectively. There was a pronounced clustering pattern of SAD on south-facing slopes due to relatively drier and warmer conditions, but no apparent spatial gradient was found for elevation and slope. This study demonstrates the feasibility of utilizing remote sensing to assess the ramification of climate-induced forest mortality on ecosystems and suggests promising opportunities for systematic large-scale C dynamics monitoring of tree dieback, which would improve estimates of C budgets of North America with climate change.

Description: Maincrop potato yields in Scotland have increased by 30-35 t ha −1 since 1960 as a result of many changes, but has changing climate contributed anything to this? The purpose of this work was to answer this question. Daily weather data for the period 1960 to 2006 were analysed for five locations covering the zones of potato growing on the east coast of Scotland (between 55.213 and 57.646 N) to determine trends in temperature, rainfall and solar radiation. A physiologically-based potato yield model was validated using data obtained from a long-term field trial in eastern Scotland, and then employed to simulate crop development and potential yield at each of the five sites. Over the 47 years, there were significant increases in annual air and 30 cm soil temperatures (0.27 K decade −1 and 0.30 K decade −1 respectively), but no significant changes in annual precipitation or in the timing of the last frost in spring and the first frost of autumn. There was no evidence of any north to south gradient of warming. Simulated emergence and canopy closure became earlier at all five sites over the period with the advance being greater in the north (3.7 and 3.6 days decade −1 respectively) than the south (0.5 and 0.8 days decade −1 respectively). Potential yield increased with time, generally reflecting the increased duration of the green canopy, at average rates of 2.8 t ha −1 decade −1 for chitted seed (sprouted prior to planting) and 2.5 t ha −1 decade −1 for unchitted seed. The measured warming could contribute potential yield increases of up to 13.2 t ha −1 for chitted potato (range 7.1 - 19.3 t ha −1 ) and 11.5 t ha −1 for unchitted potato (range 7.1 - 15.5 t ha −1 ) equivalent to 34-39% of the increased potential yield over the period or 23-26% of the increase in actual measured yields.

Description: Africa is predicted to be highly vulnerable to 21 st century climatic changes. Assessing the impacts of these changes on Africa's biodiversity is, however, plagued by uncertainties, and markedly different results can be obtained from alternative bioclimatic envelope models or future climate projections. Using an ensemble forecasting framework, we examine projections of future shifts in climatic suitability, and their methodological uncertainties, for over 2,500 species of mammals, birds, amphibians and snakes in sub-Saharan Africa. To summarise a priori the variability in the ensemble of 17 general circulation models, we introduce a consensus methodology that combines co-varying models. Thus we quantify and map the relative contribution to uncertainty of seven bioclimatic envelope models, three multi-model climate projections and three emissions scenarios, and explore the resulting variability in species turnover estimates. We show that bioclimatic envelope models contribute most to variability, particularly in projected novel climatic conditions over Sahelian and southern Saharan Africa. To summarise agreements among projections from the bioclimatic envelope models we compare five consensus methodologies, which generally increase or retain projection accuracy and provide consistent estimates of species turnover. Variability from emissions scenarios increases towards late-century and affects southern regions of high species turnover centred in arid Namibia. Two-fold differences in median species turnover across the study area emerge among alternative climate projections and emissions scenarios. Our ensemble of projections underscores the potential bias when using a single algorithm or climate projection for Africa, and provides a cautious first approximation of the potential exposure of sub-Saharan African vertebrates to climatic changes. The future use and further development of bioclimatic envelope modelling will hinge on the interpretation of results in the light of methodological as well as biological uncertainties. Here, we provide a framework to address methodological uncertainties and contextualise results.

Description: Climate change is expected to be a significant threat to biodiversity, including crop diversity at centers of origin and diversification. As a way to avoid food scarcity in the future, it is important to have a better understanding of the possible impacts of climate change on crops. We evaluated these impacts on maize, one of the most important crops worldwide, and its wild relatives Tripsacum and Teocintes. Maize is the staple crop in Mexico and Mesoamerica and there are currently about 59 described races in Mexico, its center of origin. In this study, we modeled the distribution of maize races and of its wild relatives in Mexico for the present and in two time periods in the future (2030 and 2050), to identify the potentially most vulnerable taxa and geographic regions in the face of climate change. Bioclimatic distribution of crops has seldom been modeled, probably because social and cultural factors play an important role on crop suitability. Nonetheless, rainfall and temperature still represent a major influence on crop distribution pattern, particularly in rainfed crop systems under traditional agrotechnology. Such is the case of Mexican maize races and consequently, climate change impacts can be expected. Our findings generally show significant reductions of potential distribution areas by 2030 and 2050 in most cases. However, future projections of each race show contrasting responses to climatic scenarios. Several evaluated races show new potential distribution areas in the future, suggesting that proper management may favor diversity conservation. Modeled distributions of Tripsacum species and Teocintes indicate more severe impacts compared to maize races. Our projections lead to in situ and ex situ conservation recommended actions to guarantee the preservation of the genetic diversity of Mexican maize.

Description: Most temperate forests are accumulating carbon (C) and may continue to do so in the near future. However, the situation may be different in water-limited ecosystems, where the potentially positive effects of C and N fertilization and rising temperatures interact with water availability. In this study we use the extensive network of plots of two consecutive Spanish national forest inventories to identify the factors that determine the spatial variation of the C stock change, growth and mortality rate of forests in Peninsular Spain (below- and aboveground). We fitted general linear models to assess the response of C stock change and its components to the spatial variability of climate (in terms of water availability), forest structure (tree density and C stock), previous forest management, and the recent warming trend. Our results show that undisturbed forests in Peninsular Spain are accumulating C at a rate of ~1.4 Mg C ha −1 yr −1 , and that forest structural variables are the main determinants of forest growth and C stock change. Water availability was positively related to growth and C accumulation. On the other hand, recent warming has reduced growth rate and C accumulation, especially in wet areas. Spatial variation in mortality (in terms of C loss) was mostly driven by differences in growth rate across plots, and was consistent with ‘natural’, self-thinning dynamics related to the recent abandonment of forest management over large areas of Spain, with the consequent increase in tree density and competition. Interestingly, the negative effect of warming on forest C accumulation disappears if only managed stands are considered, emphasizing the potential of forest management to mitigate the effects of climate change. However, the effect of forest management was weak and, in some cases, not significant, implying the need of further research on its impact.

Description: Human activities in coastal areas frequently cause loss of benthic macrophytes (e.g. seagrasses) and concomitant increases in microalgal production through eutrophication. Whether such changes translate into shifts in the composition of sediment detritus is largely unknown, yet such changes could impact the role these ecosystems play in sequestrating CO 2 . We reconstructed the sedimentary records of cores taken from two sites within Botany Bay, Sydney – the site of European settlement of Australia – to look for human-induced changes in dominant sources of detritus in this estuary. Cores covered a period from the present day back to the middle Holocene (~6,000 y) according to 210 Pb profiles and radiocarbon ( 14 C) dating. Depositional histories at both sites couldn't be characterized by a linear sedimentation rate; sedimentation rates in the last 30-50 years were considerably higher than during the rest of the Holocene. C:N ratios declined and began to exhibit a microalgal source signature from around the time of European settlement, which could be explained by increased nutrient flows into the Bay caused by anthropogenic activity. Analysis of stable isotopic ratios of 12 C/ 13 C showed that the relative contribution of seagrass and C3 terrestrial plants (mangroves, saltmarsh) to detritus declined around the time of rapid industrial expansion (~1950's), coinciding with an increase in the contribution of microalgal sources. We conclude that the relative contribution of microalgae to detritus has increased within Botany Bay, and that this shift is the sign of increased industrialization and concomitant eutrophication. Given the lower carbon burial efficiencies of microalgae (~0.1%) relative to seagrasses and C3 terrestrial plants (up to 10%), such changes represent a substantial weakening of the carbon sink potential of Botany Bay – this occurrence is likely to be common to human-impacted estuaries, and has consequences for the role these systems play in helping to mitigate climate change.

Description: Bogs are globally important sinks of atmospheric carbon (C) due to the accumulation of partially decomposed litter that forms peat. Because bogs receive their nutrients from the atmosphere, the world-wide increase of nitrogen (N) deposition is expected to affect litter decomposition and, ultimately, the rate of C accumulation. However, the mechanism of such biogeochemical alteration remains unclear and quantification of the effect of N addition on litter accumulation has yet to be done. Here we show that seven years of N addition to a bog decreased the C:N ratio, increased the bacterial biomass and stimulated the activity of hydrolytic and oxidative enzymes in surface peat. Furthermore, N addition modified nutrient limitation of microbes during litter decomposition so that phosphorus became a primary limiting nutrient. Alteration of N release from decomposing litter affected bog water chemistry and the competitive balance between peat-forming mosses and vascular plants. We estimate that deposition of about 4 g N m −2 yr −1 will cause a mean annual reduction of fresh litter C accumulation of about 40 g m −2 primarily as a consequence of decreased litter production from peat-forming mosses. Our findings show that N deposition interacts with both above and below ground components of biodiversity to threaten the ability of bogs to act as C sinks, which may offset the positive effects of N on C accumulation seen in other ecosystems.

Description: Since 1850, glaciers in the European Alps have lost around 40% of their originally glaciated area, releasing bare forefields, which are colonized by alpine pioneer species, setting the scene for later successional stages. These expanding pioneer communities are likely less restricted by resources and competition than late successional systems, we thus hypothesized that rising atmospheric CO 2 concentration will enhance plant growth in these high-elevation communities. Nine characteristic, perennial glacier forefield species were assembled in microcosms and grown at a nearby experimental site in the Swiss Alps (2440 m a.s.l.). The communities were exposed to an elevated CO 2 concentration of 580 ppm by Free Air CO 2 Enrichment (FACE) for three seasons. Four study species were additionally grown in isolation in containers, half of which received a low dose of mineral fertilizer in order to explore a potential nutrient limitation of the CO 2 response. Responses of growth dynamics and peak season biomass of the two graminoid species, four forbs and three cushion forming species were analysed by repeated non-destructive assessments and a final biomass harvest. After three seasons, none of the species were stimulated by elevated CO 2 , irrespective of mineral nutrient addition, which by itself enhanced growth in the fertilized plants by +34% on average. Increased CO 2 concentration did not affect total (above- plus belowground) biomass but reduced aboveground biomass by –35% across all species, even in the fast growing ones. This reduced aboveground biomass was associated with higher biomass partitioning to roots. Foliar non-structural carbohydrate (NSC) concentration increased and nitrogen concentration in leaves decreased under elevated CO 2 . We observed downward adjustment of photosynthetic capacity by on average –26% under long-term exposure to 580 ppm CO 2 (assessed in graminoids only). Our results indicate that glacier forefield pioneers, growing under harsh climatic conditions are not carbon limited at current atmospheric CO 2 concentration.

Description: The sensitivity of early plant regeneration to environmental change makes regeneration a critical stage for understanding species response to climate change. We investigated the spatial and temporal response of eucalypt trees in the Central Highland region of south eastern Australia to high and low climate change scenarios. We developed a novel mechanistic model incorporating germination processes, TACA-GEM, to evaluate establishment probabilities of five key eucalypt species, Eucalyptus pauciflora, E. delegatensis, E. regnans, E. nitens, and E. obliqua . Changes to regeneration potential at landscape and site levels were calculated to determine climate thresholds. Model results demonstrated that climate change is likely to impact on plant regeneration. We observed increases and decreases of regeneration potential depending on the ecosystem, indicating that some species will increase in abundance in some forest types whilst other forest types will become inhabitable. In general the dry forest ecosystems were most impacted whilst the wet forests were least impacted. We also observed that species with seed dormancy mechanisms, like E. pauciflora and E. delegatensis , are likely to be at higher risk than those without. Landscape and site level analysis revealed heterogeneity in species response at different scales. On a landscape scale, a 4.3°C mean temperature increase and 22% decline in precipitation (predicted for 2080) is predicted to be a threshold for large spatial shifts in species regeneration niches across the study region, while a 2.6°C increase and 15% decline in precipitation (predicted for 2050) will likely result in local site-level shifts. Site-level analysis showed that considerable declines in regeneration potential for E. delegatensis , E. pauciflora , and E. nitens were modelled to occur in some ecosystems by 2050. While overall model performance and accuracy was good, better understanding of effects from extreme events and other underlying processes on regeneration will improve modelling and development of species conservation strategies.

Description: Riparian ecosystems, already greatly altered by water management, land development and biological invasion, are being further altered by increasing atmospheric CO 2 concentrations ([CO 2 ]) and climate change, particularly in arid and semiarid (dryland) regions. In this literature review, we (1) summarize expected changes in [CO 2 ], climate, hydrology and water management in dryland western North America, (2) consider likely effects of those changes on riparian ecosystems, and (3) identify critical knowledge gaps. Temperatures in the region are rising and droughts are becoming more frequent and intense. Warmer temperatures in turn are altering river hydrology: advancing the timing of spring snowmelt floods, altering flood magnitudes, and reducing summer and base flows. Direct effects of increased [CO 2 ] and climate change on riparian ecosystems may be similar to effects in uplands, including increased heat and water stress, altered phenology and species geographic distributions, and disrupted trophic and symbiotic interactions. Indirect effects due to climate-driven changes in streamflow, however, may exacerbate the direct effects of warming and increase the relative importance of moisture and fluvial disturbance as drivers of riparian ecosystem response to global change. Together, climate change and climate-driven changes in streamflow are likely to reduce abundance of dominant, native, early-successional tree species, favor herbaceous species and both drought-tolerant and late-successional woody species (including many introduced species), reduce habitat quality for many riparian animals, and slow litter decomposition and nutrient cycling. Climate-driven changes in human water demand and associated water management may intensify these effects. On some regulated rivers, however, reservoir releases could be managed to protect riparian ecosystem services. Immediate research priorities include determining riparian species environmental requirements and monitoring riparian ecosystems to allow rapid detection and response to undesirable ecological change.

Description: Climate change and habitat loss are both key threatening processes driving the global loss in biodiversity. Yet little is known about their synergistic effects on biological populations due to the complexity underlying both processes. If the combined effects of habitat loss and climate change are greater than the effects of each threat individually, current conservation management strategies may be inefficient and at worst ineffective. Therefore, there is a pressing need to identify whether interacting effects between climate change and habitat loss exist and, if so, quantify the magnitude of their impact. In this paper, we present a meta-analysis of studies that quantify the effect of habitat loss on biological populations and examine whether the magnitude of these effects depends on current climatic conditions and historical rates of climate change. We examined 1,319 papers on habitat loss and fragmentation, identified from the past 20 years, representing a range of taxa, landscapes, land-uses, geographic locations and climatic conditions. We find that current climate and climate change are important factors determining the negative effects of habitat loss on species density and/or diversity. The most important determinant of habitat loss and fragmentation effects, averaged across species and geographic regions, was current maximum temperature, with mean precipitation change over the last 100 years of secondary importance. Habitat loss and fragmentation effects were greatest in areas with high maximum temperatures. Conversely, they were lowest in areas where average rainfall has increased over time. To our knowledge, this is the first study to conduct a global terrestrial analysis of existing data to quantify and test for interacting effects between current climate, climatic change and habitat loss on biological populations. Understanding the synergistic effects between climate change and other threatening processes has critical implications for our ability to support and incorporate climate change adaptation measures into policy development and management response.

Description: The ability to use δ 18 O values of nitrous oxide (N 2 O) to apportion environmental emissions is currently hindered by a poor understanding of the controls on δ 18 O-N 2 O from nitrification (hydroxylamine oxidation to N 2 O and nitrite reduction to N 2 O). In this study fertilized agricultural soils and unfertilized temperate forest soils were aerobically incubated with different 18 O/ 16 O waters, and conceptual and mathematical models were developed to systematically explain the δ 18 O-N 2 O formed by nitrification. Modelling exercises used a set of defined input parameters to emulate the measured soil δ 18 O-N 2 O data (Monte Carlo approach). The Monte Carlo simulations implied that abiotic oxygen (O) exchange between NO 2 − and H 2 O is important in all soils, but that biological, enzyme-controlled O-exchange does not occur during the reduction of NO 2 − to N 2 O (nitrifier-denitrification). Similarly, the results of the model simulations indicated that N 2 O consumption is not characteristic of aerobic N 2 O formation. The results of this study and a synthesis of the published literature data indicate that δ 18 O-N 2 O formed in aerobic environments is constrained between +13‰ and +35‰ relative to VSMOW. N 2 O formed via hydroxylamine oxidation and nitrifier-denitrification cannot be separated using δ 18 O unless 18 O tracers are employed. The natural range of nitrifier δ 18 O-N 2 O is discussed and explained in terms of our conceptual model, and the major and minor controls that define aerobically-produced δ 18 O-N 2 O are identified. Despite the highly complex nature of δ 18 O-N 2 O produced by nitrification this δ 18 O range is narrow. As a result, in many situations δ 18 O values may be used in conjunction with δ 15 N-N 2 O data to apportion nitrifier- and denitrifier-derived N 2 O. However, when biological O-exchange during denitrification is high and N 2 O consumption is low, there may be too much overlap in δ 18 O values to distinguish N 2 O formed by these pathways.

Description: Effects of climate warming on wild populations of organisms are expected to be greatest at higher latitudes, paralleling greater anticipated increases in temperature in these regions. Yet, these expectations assume that populations in different regions and taxa are equally susceptible to the effects of warming. This is unlikely to be the case. Here, we develop a series of predictive models for physiological thermal tolerances in ants based on current and future climates. We found that tropical ants have lower warming tolerances, a metric of susceptibility to climate warming, than temperate ants despite greater increases in temperature at higher latitudes. Using climatic, ecological and phylogenetic data, we refine our predictions of which ants (across all regions) were most susceptible to climate warming. We found that ants occupying warmer and more mesic forested habitats at lower elevations are the most physiologically susceptible to deleterious effects of climate warming. Phylogenetic history was also a strong indicator of physiological susceptibility. In short, we find that ants that live in the canopies of hot, tropical forest are the most at risk, globally, from climate warming. Unfortunately this is where many, perhaps most, ant and other species on Earth live.

Description: Forest insects and pathogens are major disturbance agents that have affected millions of hectares in North America in recent decades, implying significant impacts to the carbon (C) cycle. Here we review and synthesize published studies of the effects of biotic disturbances on forest C cycling in the United States and Canada. Primary productivity in stands was reduced, sometimes considerably, immediately following insect or pathogen attack. After repeated growth reductions caused by some insects or pathogens or a single infestation by some bark beetle species, tree mortality occurred, altering productivity and decomposition. In the years following disturbance, primary productivity in some cases increased rapidly as a result of enhanced growth by surviving vegetation, and in other cases increased slowly because of lower forest regrowth. In the decades following tree mortality, decomposition increased as a result of the large amount of dead organic matter. Net ecosystem productivity decreased immediately following attack, with some studies reporting a switch to a C source to the atmosphere, and increased afterward as the forest regrew and dead organic matter decomposed. Large variability in C cycle responses arose from several factors, including type of insect or pathogen, time since disturbance, number of trees affected, and capacity of remaining vegetation to increase growth rates following outbreak. We identified significant knowledge gaps, including limited understanding of carbon cycle impacts among different biotic disturbance types (particularly pathogens), their impacts at landscape and regional scales, and limited capacity to predict disturbance events and their consequences for carbon cycling. We conclude that biotic disturbances can have major impacts on forest C stocks and fluxes and can be large enough to affect regional C cycling. However, additional research is needed to reduce the uncertainties associated with quantifying biotic disturbance effects on the North American C budget.

Description: Earthworms can increase nitrous oxide ( N 2 O ) emissions, particularly in no-tillage systems where earthworms are abundant. Here, we study the effect of residue incorporation depth on earthworm-induced N 2 O emissions. We hypothesized that cumulative N 2 O emissions decrease with residue incorporation depth, because (i) increased water filled pore space (WFPS) in deeper soil layers leads to higher denitrification rates as well as more complete denitrification; and (ii) the longer upward diffusion path increases N 2 O reduction to N 2 . Two 84-day laboratory mesocosm experiments were conducted. First, we manually incorporated maize ( Z ea mays L.) residue at different soil depths (incorporation experiment). Second, 13 C -enriched maize residue was applied to the soil surface and anecic species L umbricus terrestris (L.) and epigeic species L umbricus rubellus (Hoffmeister) were confined to different soil depths (earthworm experiment). Residue incorporation depth affected cumulative N 2 O emissions in both experiments ( P  〈   0.001). In the incorporation experiment, N 2 O emissions decreased from 4.91 mg  N 2 O–N  kg −1 soil (surface application) to 2.71 mg  N 2 O–N  kg −1 soil (40–50 cm incorporation). In the earthworm experiment, N 2 O emissions from L . terrestris decreased from 3.87 mg  N 2 O–N  kg −1 soil (confined to 0–10 cm) to 2.01 mg  N 2 O–N  kg −1 soil (confined to 0–30 cm). Both experimental setups resulted in dissimilar WFPS profiles that affected N 2 O dynamics. We also found significant differences in residue C recovery in soil organic matter between L . terrestris (28–41%) and L . rubellus (56%). We conclude that (i) N 2 O emissions decrease with residue incorporation depth, although this effect was complicated by dissimilar WFPS profiles; and (ii) larger residue C incorporation by L . rubellus than L . terrestris indicates that earthworm species differ in their C stabilization potential. Our findings underline the importance of studying earthworm diversity in the context of greenhouse gas emissions from agro-ecosystems.

Description: Phenology, by controlling the seasonal activity of vegetation on the land surface, plays a fundamental role in regulating photosynthesis and other ecosystem processes, as well as competitive interactions and feedbacks to the climate system. We conducted an analysis to evaluate the representation of phenology, and the associated seasonality of ecosystem-scale CO 2 exchange, in 14 models participating in the North American Carbon Program Site Synthesis. Model predictions were evaluated using long-term measurements (emphasizing the period 2000-2006) from 10 forested sites within the AmeriFlux and Fluxnet-Canada networks. In deciduous forests, almost all models consistently predicted that the growing season started earlier, and ended later, than was actually observed; biases of 2 weeks or more were typical. For these sites, most models were also unable to explain more than a small fraction of the observed interannual variability in phenological transition dates. Finally, for deciduous forests, misrepresentation of the seasonal cycle resulted in over-prediction of gross ecosystem photosynthesis by +160 ± 145 g C m −2 y −1 during the spring transition period, and +75 ± 130 g C m −2 y −1 during the autumn transition period (13% and 8% annual productivity, respectively) compensating for the tendency of most models to under-predict the magnitude of peak summertime photosynthetic rates. Models did a better job of predicting the seasonality of CO 2 exchange for evergreen forests. These results highlight the need for improved understanding of the environmental controls on vegetation phenology, and incorporation of this knowledge into better phenological models. Existing models are unlikely to predict future responses of phenology to climate change accurately, and therefore will misrepresent the seasonality and interannual variability of key biosphere-atmosphere feedbacks and interactions in coupled global climate models.

Description: The Antarctic has experienced major changes in temperature, wind speed and stratospheric ozone levels during the last 50 years. However until recently continental Antarctica appeared to be little impacted by climate warming, thus biological changes were predicted to be relatively slow. Detecting the biological effects of Antarctic climate change has been hindered by the paucity of long-term data sets, particularly for organisms that have been exposed to these changes throughout their lives. We show that radiocarbon signals are preserved along shoots of the dominant Antarctic moss flora and use these to determine accurate growth rates over a period of several decades, allowing us to explore the influence of environmental variables on growth and providing a dramatic demonstration of the effects of climate change. We have generated detailed 50-year growth records for Ceratodon purpureus and three other Antarctic moss species using the 1960s radiocarbon bomb spike. Our growth rate and stable carbon isotope (δ 13 C) data show that C. purpureus ’ growth rates are correlated with key climatic variables, and furthermore that the observed effects of climate variation on growth are mediated through changes in water availability. Our results indicate the timing and balance between warming, high wind speeds and elevated UV fluxes may determine the fate of these mosses and the associated communities that form oases of Antarctic biodiversity.

Description: As a clear consensus is emerging that habitat for many species will dramatically reduce or shift with climate change, attention is turning to adaptation strategies to address these impacts. Assisted colonization is one such strategy that has been predominantly discussed in terms of the costs of introducing potential competitors into new communities and the benefits of reducing extinction risk. However, the success or failure of assisted colonization will depend on a range of population-level factors that have not yet been quantitatively evaluated—the quality of the recipient habitat, the number and life stages of translocated individuals, the establishment of translocated individuals in their new habitat and whether the recipient habitat is subject to ongoing threats all will play an important role in population persistence. In this paper, we do not take one side or the other in the debate over whether assisted colonization is worthwhile. Rather, we focus on the likelihood that assisted colonization will promote population persistence in the face of climate-induced distribution changes and altered fire regimes for a rare endemic species. We link a population model with species distribution models (SDMs) to investigate expected changes in populations with climate change, the impact of altered fire regimes on population persistence, and how much assisted colonization is necessary to minimize risk of decline in populations of Tecate cypress, a rare endemic tree in the California Floristic Province, a biodiversity hotspot. We show that assisted colonization may be a risk-minimizing adaptation strategy when there are large source populations that are declining dramatically due to habitat contractions, multiple nearby sites predicted to contain suitable habitat, minimal natural dispersal, high rates of establishment of translocated populations, and the absence of non-climatic threats such as altered disturbance regimes. However, when serious ongoing threats exist, assisted colonization is ineffective.

Description: Northern peatlands are a major natural source of methane (CH 4 ) to the atmosphere. Permafrost conditions and spatial heterogeneity are two of the major challenges for estimating CH 4 fluxes from the northern high latitudes. This study reports the development of a new model to upscale CH 4 fluxes from plant communities to ecosystem scale in permafrost peatlands by integrating an existing biogeochemical model (DNDC) with a permafrost model (NEST). A new ebullition module was developed to track the changes of bubble volumes in the soil profile based on the ideal gas law and Henry's law. The integrated model was tested against observations of CH 4 fluxes measured by closed chambers and eddy covariance method in a polygonal permafrost area in the Lena River Delta, Russia. Results from the tests showed that the simulated soil temperature, summer thaw depths and CH 4 fluxes were in agreement with the measurements at the five chamber observation sites; and the modeled area-weighted average CH 4 fluxes were similar to the eddy covariance observations in seasonal patterns and annual totals though discrepancy existed in shorter time-scales. This study indicates that the integrated model, NEST-DNDC, is capable of upscaling CH 4 fluxes from plant communities to larger spatial scales.

Description: Elevated environmental temperatures associated with anthropogenic warming have the potential to impact host-parasite interactions, with consequences for population health and ecosystem functioning. One way that elevated temperatures might influence parasite prevalence and intensity is by increasing life cycle completion rates. Here we investigate how elevated temperatures impact a critical phase of the life cycle of the bird tapeworm Schistocephalus solidus – the growth of plerocercoid larvae in host sticklebacks Gasterosteus aculeatus . By 8 weeks post-infection, plerocercoids recovered from experimentally infected sticklebacks held at 20C weighed on average 104.9mg, with all exceeding 50mg, the mass considered consistently infective to definitive hosts. In contrast, plerocercoids from sticklebacks held at 15C weighed on average 26.5mg, with none exceeding 50mg. Because small increases in plerocercoid mass affect adult fecundity disproportionately in this species, enhanced plerocercoid growth at higher temperatures predicts dramatically increased output of infective parasite stages. Subsequent screening of thermal preferences of sticklebacks from a population with endemic S. solidus infection demonstrated that fish harbouring infective plerocercoids show significant preferences for warmer temperatures. Our results therefore indicate that parasite transmission might be affected in at least two ways under anthropogenic warming; by enhancing rates of parasite growth and development, and by increasing the likelihood of hosts being able to seek out proliferating warmer microhabitats. Furthermore, our results suggest the potential for positive feedback between parasite growth and host thermal preferences, which could dramatically increase the effects of even small temperature increases. We discuss the possible mechanisms underpinning our results, their likely ecological consequences and highlight key areas for further research.

Description: Several major articles from the past decade and beyond conclude the impact of re- or af-forestation on water yield is negative: additional forest cover will reduce and removing forests will raise downstream water availability. A second group of authors argue the opposite: planting additional forests should raise downstream water availability and intensify the hydrologic cycle. Obtaining supporting evidence for this second group of authors has been more difficult due to the larger scales at which the positive effects of forests on the water cycle may be seen. We argue that forest cover is inextricably linked to precipitation. Forest-driven evapotranspiration removed from a particular catchment contributes to the availability of atmospheric moisture vapor and its cross-continental transport, raising the likelihood of precipitation events and increasing water yield, in particular in continental interiors more distant from oceans. Seasonal relationships heighten the importance of this phenomenon. We review the arguments from different scales and perspectives. This clarifies the generally beneficial relationship between forest cover and the intensity of the hydrologic cycle. While evidence supports both sides of the argument—trees can reduce runoff at the small catchment scale—at larger scales, trees are more clearly linked to increased precipitation and water availability. Progressive deforestation, land conversion from forest to agriculture and urbanization have potentially negative consequences for global precipitation, prompting us to think of forest ecosystems as global public goods . Policy-making attempts to measure product water footprints, estimate the value of ecosystem services, promote afforestation, develop drought mitigation strategies and otherwise manage land use must consider the linkage of forests to the supply of precipitation.

Description: The worldwide effects of ocean acidification (OA) on marine species are a growing concern. In temperate coastal seas, seaweeds are dominant primary producers that create complex habitats and supply energy to higher trophic levels. Studies on OA and macroalgae have focused on calcifying species and adult stages but, critically, they have overlooked the microscopic stages of the reproductive life cycle, which, for other anthropogenic stress e.g. UV-B radiation, are the most susceptible life-history phase. Also, environmental cues and stressors can cause changes in the sex ratio which has implications for the mating system and recruitment success. Here, we report the effects of pH (7.59–8.50) on meiospore germination and sex determination for the giant kelp, Macrocystis pyrifera (Laminariales), in the presence and absence of additional dissolved inorganic carbon (DIC). Lowered pH (7.59–7.60, using HCl-only) caused a significant reduction in germination, while added DIC had the opposite effect, indicating that increased CO 2 at lower pH ameliorates physiological stress. This finding also highlights the importance of appropriate manipulation of seawater carbonate chemistry when testing the effects of ocean acidification on photosynthetic organisms. The proportion of male to female gametophytes did not vary significantly between treatments suggesting that pH was not a primary environmental modulator of sex. Relative to the baseline (pH 8.19), gametophytes were 32% larger under moderate OA (pH 7.86) compared to their size (10% increase) under extreme OA (pH 7.61). This study suggests that metabolically-active cells can compensate for the acidification of seawater. This homeostatic function minimises the negative effects of lower pH (high H + ions) on cellular activity. The 6–9% reduction in germination success under extreme OA suggests that meiospores of M . pyrifera may be resistant to future ocean acidification.

Description: Most large-scale multi-species studies of tree growth have been conducted in tropical and cool temperate forests, whereas Mediterranean water-limited ecosystems have received much less attention. This limits our understanding of how growth of coexisting tree species varies along environmental gradients in these forests, and the implications for species interactions and community assembly under current and future climatic conditions. Here, we quantify the absolute effect and relative importance of climate, tree size and competition as determinants of tree growth patterns in Iberian forests, and explore inter-specific differences in the two components of competitive ability (competitive response and effect) along climatic and size gradients. Spatially-explicit neighborhood models were developed to predict tree growth for the 15 most abundant Iberian tree species using permanent-plot data from the Spanish Second and Third National Forest Inventory (IFN). Our neighborhood analyses showed a climatic and size effect on tree growth, but also revealed that competition from neighbors has a comparatively much larger impact on growth in Iberian forests. Moreover, the sensitivity to competition (i.e. competitive response) of target trees varied markedly along climatic gradients causing significant rank reversals in species performance, particularly under xeric conditions. We also found compelling evidence for strong species-specific competitive effects in these forests. Altogether, these results constitute critical new information which not only furthers our understanding of important theoretical questions about the assembly of Mediterranean forests, but will also be of help in developing new guidelines for adapting forests in this climatic boundary to global change. If we consider the climatic gradients of this study as a surrogate for future climatic conditions, then we should expect absolute growth rates to decrease and sensitivity to competition to increase in most forests of the Iberian Peninsula (in all but the northern Atlantic forests), making these management considerations even more important in the future.

Description: Gas exchange and water relations were evaluated under full-season in situ infrared (IR) warming for hard red spring wheat ( Triticum aestivum L. cv. Yecora Rojo) grown in an open field in a semiarid desert region of the Southwest USA. A T-FACE ( T emperature F ree- A ir C ontrolled E nhancement) apparatus utilizing IR heaters maintained canopy air temperature above 3.0-m Heated plots of wheat by 1.3 and 2.7°C (0.2 and 0.3°C below the targeted set-points of Reference plots with dummy heaters) during daytime and nighttime, respectively. Control plots had no apparatus. Every six weeks during 2007–2009 wheat was sown under the three warming treatments (i.e., Control, Heated, Reference) in three replicates in a 3x3 Latin Square (LSQ) design on six plantings during four months (i.e., Jan., Mar., Sept., Dec.), or in a natural temperature variation treatment (i.e., Control) in three replicates in a Randomized Complete Block (RCB) design on nine plantings during seven months (i.e., Jan., Feb., Apr., June, July, Aug., Oct.). Soil temperature ( T s ) and volumetric soil-water content ( θ s ) were 1.3°C warmer and 14% lower in Heated compared with Reference plots, respectively. Other than a 1% shading effect, no artifacts on gas exchange or water relations were associated with the IR warming apparatus. Infrared warming increased carbon gain characteristic of an increase in metabolic rates to higher temperature that may have been attributed to the well-watered wheat crop and the supplemental irrigation that minimized plant-to-air water vapour pressure differences between IR-warmed and non-warmed plots. Nevertheless, seasonal oscillations in the IR warming response on carbon gain occurred. Infrared warming decreased leaf water status and provided thermal protection during freeze events. Infrared warming is an effective experimental methodology to investigate the impact of global climate change on agronomic cropping and natural ecosystems to a wide range of natural and artificially imposed air temperatures.

Description: The capacity of peatlands in the northern hemisphere to provide carbon storage, maintain water quality and support northern biodiversity is threatened by a combination of climate change and inappropriate land management. Historical drainage and increasing temperatures threaten the maintenance of the high water tables required for effective peatland functioning, and there is an urgent need to develop appropriate adaptation strategies. Here we use a large-scale replicated experimental design to test the effects of artificial drainage and drain blocking upon soil moisture and cranefly (Diptera: Tipulidae) abundance. Craneflies constitute a key component of peatland biological communities; they are important herbivores and a major prey item for breeding birds. However, they are also susceptible to drought, so are at risk from future climate change. We found that cranefly abundance increased with soil moisture, in a wedge-shaped relationship; high soil moisture is a necessary condition for high cranefly abundance. Blocking drains increased both soil moisture (by 0.06 m 3  m −3 in 2009 and 0.23 m 3  m −3 in 2010) and cranefly abundance (1.3-fold in 2009, 4.5-fold in 2010), but the strength and significance of the effects varied between years. The benefits of restoring ecosystem moisture levels are likely to be greatest during dry years and at dry sites. This study provides some of the first evidence that adaptation management can potentially reduce some of the negative effects of climate change on vulnerable peatland systems. Management to maintain or increase soil moisture in peatlands can therefore be expected to increase populations of craneflies and their avian predators (which are of conservation and economic interest), but also increase the resilience of the ecosystem to future warming and increasingly frequent droughts, and improve carbon storage and water quality.

Description: Ecological studies relating population parameters to climate conditions are limited by a lack of experimental control systems and rely instead on correlative evidence to draw inferences about how populations respond to environmental forcing. Consequently, some correlations turn out to be spurious and not ecologically meaningful. To strengthen inferences, multiple populations may be examined simultaneously to confirm whether relationships can be generalized across multiple systems; however, this assumes that populations respond similarly to climate drivers, ignoring the potential for ecological complexity. Using data on eight sockeye salmon populations from southwestern Alaska, we constructed a series of models based on ecological hypotheses, relating salmon population productivity to climate factors experienced at different life stages. We modeled populations at a range of organizational scales, from distinct populations, to populations grouped by common nursery lake, to all populations within a watershed, and determined the relative statistical support for climate drivers at each scale. In general, warmer lake and sea surface temperatures in the summer coincided with increased productivity of these populations, but the most sensitive life-stage for climate effects varied among populations, particularly among nursery lakes. The best model when considering all populations together, despite strong statistical support, failed to represent the complexity which became evident when populations were modeled by common nursery lake, or independently. These results emphasize that the most appropriate organizational scale to model salmon stocks will depend on specific management, scientific, or conservation goals.

Description: A soil-plant-atmosphere model was used to estimate gross primary productivity (GPP) and evapotranspiration (ET) of a tropical savanna in Australia. This paper describes model modifications required to simulate the substantial C4 grass understory together with C3 trees. The model was further improved to include a seasonal distribution of leaf area and foliar nitrogen through ten canopy layers. Model outputs were compared to a five year eddy covariance dataset. Adding the C4 photosynthesis component improved the model efficiency and root-mean-squared error (RMSE) for total ecosystem GPP by better emulating annual peaks and troughs in GPP across wet and dry seasons. The C4 photosynthesis component had minimal impact on modelled values of ET. Outputs of GPP from the modified model agreed well with measured values, explaining between 79–90% of the variance and having a low RMSE (0.003–0.281 g C m −2  d −1 ). Approximately 40% of total annual GPP was contributed by C4 grasses. Total (trees and grasses) wet season GPP was approximately 75–80% of total annual GPP. Light-use-efficiency (LUE) was largest for the wet season and smallest in the dry season and C4 LUE was larger than that of the trees. A sensitivity analysis of GPP revealed that daily GPP was most sensitive to changes in leaf area index (LAI) and foliar nitrogen (N f ) and relatively insensitive to changes in maximum carboxylation rate (V cmax ), maximum electron transport rate (J max ) and minimum leaf water potential ( ψ min ). The modified model was also able to represent daily and seasonal patterns in ET, (explaining 68–81% of variance) with a low RMSE (0.038–0.19 mm d −1 ). Current values of N f , LAI and other parameters appear to be co-limiting for maximising GPP. By manipulating LAI and soil moisture content inputs, we show that modelled GPP is limited by light interception rather than water availability at this site.

Description: Analysis of monthly coastal upwelling intensities revealed two seasonal and biologically relevant “modes” of upwelling in the California Current Ecosystem (CCE). The first mode reflected peak upwelling during the summer months and was characterized by low-frequency (multidecadal) processes, including significant (p〈0.01) linear trends at some latitudes. In contrast, the second mode reflected wintertime upwelling and was defined by higher-frequency variability associated with the North Pacific High and El Niño Southern Oscillation events. These modes were compared to multidecadal time series of splitnose rockfish ( Sebastes diploproa ) otolith growth, yelloweye rockfish ( S. ruberrimus ) otolith growth, Chinook salmon ( Oncorhynchus tshawytscha ) scale growth, and indices of Cassin's auklet ( Ptychoramphus aleuticus ) and common murre ( Uria aalge ) reproduction in the central CCE. In redundancy and correlation analyses, salmon growth and Cassin's auklet fledgling success associated with the summer upwelling mode while all other time series associated with the winter upwelling mode, indicating that CCE biology was differentially sensitive to these seasonal upwelling patterns. Thus, upwelling occurred in unrelated seasonal modes with contrasting trends, atmospheric forcing mechanisms, and impacts on the biology of the CCE, underscoring the importance of seasonality when evaluating ecosystem response to climate variability and change.

Description: Tropical forests are a significant global source of the greenhouse gas nitrous oxide (N 2 O). Predicted environmental changes for this biome highlight the need to understand how simultaneous changes in precipitation and labile carbon (C) availability may affect soil N 2 O production. We conducted a small-scale throughfall and leaf litter manipulation in a lowland tropical forest in southwestern Costa Rica to test how potential changes in both water and litter derived labile C inputs to soils may alter N 2 O emissions. Experimentally reducing throughfall in this wet tropical forest significantly increased soil emissions of N 2 O, and our data suggest that at least part of this response was driven by an increase in the concentration of dissolved organic carbon [DOC] inputs delivered from litter to soil under the drier conditions. Furthermore, [DOC] was significantly correlated with N 2 O emissions across both throughfall and litterfall manipulation plots, despite the fact that native NO 3 − pools in this site were generally small. Our results highlight the importance of understanding not only the potential direct effects of changing precipitation on soil biogeochemistry, but also the indirect effects resulting from interactions between the hydrologic, C and N cycles. Finally, over all sampling events we observed lower mean N 2 O emissions (〈1 ng N 2 O-N cm −2 h −1 ) than reported for many other lowland tropical forests, perhaps reflecting a more general pattern of increasing relative N constraints to biological activity as one moves from drier to wetter portions of the lowland tropical forest biome.

Description: Given the threatened status of many primate species, the impacts of global warming on primate reproduction and, consequently, population growth should be of concern. We examined relations between climatic variability and birth seasonality, offspring production, and infant sex ratios in two ateline primates, northern muriquis and woolly monkeys. In both species, the annual birth season was delayed by dry conditions and El Niño years, and delayed birth seasons were linked to lower birth rates. Additionally, increased mean annual temperatures were associated with lower birth rates for northern muriquis. Offspring sex ratios varied with climatic conditions in both species, but in different ways: directly in woolly monkeys, and indirectly in northern muriquis. Woolly monkeys displayed an increase in the proportion of males among offspring in association with El Niño events, whereas in northern muriquis, increases in the proportion of males among offspring were associated with delayed onset of the birth season, which itself was related, although weakly, to warm, dry conditions. These results illustrate that global warming, increased drought frequency, and changes in the frequency of El Niño events could limit primate reproductive output, threatening the persistence and recovery of ateline primate populations.

Description: Earth system models associate the ongoing global warming with increasing frequency and intensity of extreme events such as droughts and heat waves. The carbon balance of soils may be more sensitive to the impact of such extremes than to homogeneously distributed changes in soil temperature ( T s ) or soil water content ( θ s ). One parameter influenced by more pronounced drying/rewetting cycles or increases in T s is the wettability of soils. Results from laboratory and field studies showed that low θ s , particularly in combination with high T s can increase soil water repellency (SWR). Recent studies have provided evidence that the stability of soil organic matter (SOM) against microbial decomposition is substantially enhanced in water repellent soils. This review hypothesizes that SWR is an important SOM stabilization mechanism that could become more important because of the increase in extreme events. We discuss wettability-induced changes in soil moisture distribution and in soil aggregate turnover as the main mechanisms explaining the reduced mineralization of SOM with increasing SWR. The creation of preferential flow paths and subsequent uneven penetration of rainwater may cause a long-term reduction of soil water availability, affecting both microorganisms and plants. We conclude that climate change-induced SWR may intensify the effects of climatic drought and thus affect ecosystem processes such as SOM decomposition and plant productivity, as well as changes in vegetation – and microbial community structure. Future research on biosphere-climate interactions should consider the effects of increasing SWR on soil moisture and subsequently on both microbial activity and plant productivity, which ultimately determine the overall carbon balance.

Description: Large-scale soy agriculture in the southern Brazilian Amazon now rivals deforestation for pasture as the region's predominant form of land use change. Such landscape-level change can have substantial consequences for local and regional hydrology, but these effects remain relatively unstudied in this ecologically and economically important region. We examined how the conversion to soy agriculture influences water balances and stormflows using stream discharge (water yields) and the timing of discharge (stream hydrographs) in small (2.5–13.5 km 2 ) forested and soy headwater watersheds in the Upper Xingu Watershed in the state of Mato Grosso, Brazil. We monitored water yield for 1 year in three forested and four soy watersheds. Mean daily water yields were approximately four times higher in soy than forested watersheds, and soy watersheds showed greater seasonal variability in discharge. The contribution of stormflows to annual streamflow in all streams was low (〈13% of annual streamflow), and the contribution of stormflow to streamflow did not differ between land uses. If the increases in water yield observed in this study are typical, landscape-scale conversion to soy substantially alters water-balance, potentially altering the regional hydrology over large areas of the southern Amazon.

Description: In tropical areas Dynamic Global Vegetation Models (DGVMs) still have deficiencies in simulating the timing of vegetation phenology. To start addressing this problem standard Fourier-based methods are applied to aerosol screened monthly remotely sensed phenology time series (Enhanced Vegetation Index, EVI) and two major driving factors of phenology: solar radiation and precipitation (for March 2000 through December 2006 over northern South America). At 1×1 km scale using power (or variance) spectra on good quality aerosol screened time series annual cycles in EVI are detected across 58.24% of the study area, the strongest (largest amplitude) occurring in the savanna. Terra Firme forest have weak but significant annual cycles in comparison to savannas because of the heterogeneity of vegetation and non-synchronous phenological events within 1×1 km scale pixels. Significant annual cycles for radiation and precipitation account for 86% and 90% of the region respectively, with different spatial patterns to phenology. Cross-spectral analysis was used to compare separately radiation with phenology/EVI, precipitation with phenology/EVI, and radiation with precipitation. Overall the majority of the Terra Firme forest appears to have radiation as the driver of phenology (either radiation is in phase or leading phenology/EVI at the annual scale). These results are in agreement with previous research, although in Acre, central and eastern Peru and northern Bolivia there is a co-existence of ‘in phase’ precipitation over Terra Firme forest. In contrast in most areas of savanna precipitation appears to be a driver and savanna areas experiencing an inverse (anti-phase) relationship between radiation and phenology is consistent with inhibited grassland growth due to soil moisture limitation. The resulting maps provide a better spatial understanding of phenology-driver relationships offering a bench mark to parameterise ecological models.

Description: Mechanisms for inorganic carbon acquisition in macroalgal assemblages today could indicate how coastal ecosystems will respond to predicted changes in ocean chemistry due to elevated carbon dioxide (CO 2 ). We identified the proportion of non-calcifying macroalgae with particular carbon use strategies using the natural abundance of carbon isotopes and pH drift experiments in a kelp forest. We also identified all calcifying macroalgae in this system; these were the dominant component of the benthos (by % cover) at all depths and seasons while cover of non-calcareous macroalgae increased at shallower depths and during summer. All large canopy-forming macroalgae had attributes suggestive of active uptake of inorganic carbon and the presence of a CO 2 Concentration Mechanism (CCM). CCM species covered, on average, 15–45% of the benthos and were most common at shallow depths and during summer. There was a high level of variability in carbon isotope discrimination within CCM species, probably a result of energetic constraints on active carbon uptake in a low light environment. Over 50% of red non-calcifying species exhibited values below −30‰ suggesting a reliance on diffusive CO 2 uptake and no functional CCM. Non-CCM macroalgae covered on average 0–8.9% of rock surfaces and were most common in deep, low light habitats. Elevated CO 2 has the potential to influence competition between dominant coralline species (that will be negatively affected by increased CO 2 ) and non-calcareous CCM macroalgae (neutral or positive effects) and relatively rare (on a % cover basis) non-CCM species (positive effects). Responses of macroalgae to elevated CO 2 will be strongly modified by light and any responses are likely to be different at times or locations where energy constrains photosynthesis. Increased growth and competitive ability of non-calcareous macroalgae alongside negative impacts of acidification on calcifying species could have major implications for the functioning of coastal reef systems at elevated CO 2 concentrations.

Description: Climate warming and drying are modifying the fire dynamics of many boreal forests, moving them towards a regime with a higher frequency of extreme fire years characterized by large burns of high severity. Plot-scale studies indicate that increased burn severity favors the recruitment of deciduous trees in the initial years following fire. Consequently, a set of biophysical effects of burn severity on post-fire boreal successional trajectories at decadal timescales have been hypothesized. Prominent among these are a greater cover of deciduous tree species in intermediately aged stands after more severe burning, with associated implications for carbon and energy balances. Here we investigate whether the current vegetation composition of interior Alaska supports this hypothesis. A chronosequence of 6 decades of vegetation regrowth following fire was created using a database of burn scars, an existing forest biomass map, and maps of albedo and the deciduous fraction of vegetation that we derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery. The deciduous fraction map depicted the proportion of aboveground biomass in deciduous vegetation, derived using a RandomForest algorithm trained with field data sets ( n =69, 71% variance explained). Analysis of the difference Normalized Burn Ratio, a remotely sensed index commonly used as an indicator of burn severity, indicated that burn size and ignition date can provide a proxy of burn severity for historical fires. Lidar remote sensing and a bioclimatic model of evergreen forest distribution were used to further refine the stratification of the current landscape by burn severity. Our results show that since the 1950s, more severely burned areas in interior Alaska have produced a vegetation cohort that is characterized by greater deciduous biomass. We discuss the importance of this shift in vegetation composition due to climate-induced changes in fire severity for carbon sequestration in forest biomass and surface reflectance (albedo), among other feedbacks to climate.

Description: Faunal communities have been shaped in different ways by past climatic change. The impact of the termination of the last Glacial and the onset of the present (Holocene) Interglacial on large-scale faunal shifts, extinction dynamics and gene pools of species are of special interest in natural sciences. A general pattern of climate-triggered range expansion and local extinction of vertebrate species is known for Europe, and shows that in the modern temperate zone the main faunal change took place mainly during the Late Glacial (14 700–11 700 years ago) and Early Holocene (11 700–9 100 years ago). Based on large datasets of new radiocarbon data, we present precise temporal dynamics of climate-driven disappearance and appearance of reindeer and pond turtle in southern Sweden. These two species are significant climate indicators in Late Quaternary biostratigraphy. Our data reveal that the reindeer disappeared from southern Sweden ca. 10 300 years ago, whereas the pond turtle colonized the area ca. 9 860 years ago, with a 450-year gap between each species. This provides evidence for a sudden environmental turnover, causing the replacement of an arctic faunal element by a thermophilic species. The postglacial range dynamics of pond turtle and reindeer are a unique model case, allowing insights into the faunal turnover of other vertebrates during the last dramatic natural global warming event at the Pleistocene–Holocene transition.

Description: Here, we report site-to-site variability and 12–14 year trends of dissolved organic carbon (DOC) from organic layers and mineral soils of 22 forests in Bavaria, Germany. DOC concentrations in the organic layer were negatively correlated with mean annual precipitation and elevation whereas air temperature had a positive effect on DOC concentrations. DOC fluxes in subsoils increased by 3 kg ha −1  yr −1 per 100 mm precipitation or per 100 m elevation. The highest DOC concentrations were found under pine stands with mor humus. Average DOC concentrations in organic layer leachates followed the order: pine〉oak〉spruce〉beech. However, the order was different for mean DOC fluxes (spruce〉pine〉oak〉beech) because of varying precipitation regimes among the forest types. In 12 of 22 sites, DOC concentrations of organic layer leachates significantly increased by 0.5 to 3.1 mg C L −1  yr −1 during the sampling period. The increase in DOC concentration coincided with decreasing sulfate concentration, indicating that sulfate concentration is an important driver of DOC solubility in the organic layer of these forest sites. In contrast to the organic layer, DOC concentrations below 60 cm mineral soil depth decreased by 〈0.1–0.4 mg C L −1  yr −1 at eight sites. The negative DOC trends were attributed to (i) increasing adsorption of DOC by mineral surfaces resulting from desorption of sulfate and (ii) increasing decay of DOC resulting from decreasing stabilization of DOC by organo-Al complexes. Trends of DOC fluxes from organic layers were consistent with those of DOC concentrations although trends were only significant at seven sites. DOC fluxes in the subsoil were with few exceptions small and trends were generally not significant. Our results suggest that enhanced mobilization of DOC in forest floors contributed to the increase of DOC in surface waters while mineral horizons did not contribute to increasing DOC export of forest soils.

Description: Accurate estimates of the fertilization effect that elevated [CO 2 ] has on crop yields are valuable for estimation of future crop production, yet there is still some controversy over these estimates due to possible CO 2 -by-water-status interactions in chamber studies and the difficulty of conducting field experiments with elevated [CO 2 ]. This study presents a new method to estimate the CO 2 fertilization effect in dry conditions (CFE dry ), based on a combination of historical yield and climatic data and field experiments that do not require elevated [CO 2 ]. It was estimated that approximately 50 years of increasing [CO 2 ] ( i.e ., a 73 ppm increase) resulted in a 9% and 14% improvement of yield in dry conditions for maize and soybean, respectively, which is similar to estimates derived from free air CO 2 enrichment (FACE) studies. The main source of uncertainty in this approach relates to differential effects of technology trends such as new cultivars in wet versus dry years. Estimates of this technology-water interaction can be refined by further experimentation under ambient [CO 2 ], offering a cost-effective path for improving CFE estimates. The results should prove useful for modeling future yield impacts of climate change, and the approach could be used to derive estimates for other species using relatively simple yield trials.

Description: Soil methanotrophic bacteria constitute the only globally relevant biological sink for atmospheric methane (CH 4 ). Nitrogen (N) fertilizers as well as soil moisture regime affect the activity of these organisms, but the mechanisms involved are not well understood to date. In particular, virtually nothing is known about the spatial distribution of soil methanotrophs within soil structure and how this regulates CH 4 fluxes at the ecosystem scale. We studied the spatial distribution of CH 4 assimilation and its response to a factorial drought × N fertilizer treatment in a three-year experiment replicated in two grasslands differing in management intensity. Intact soil cores were labelled with 14 CH 4 and methanotrophic activity mapped at a resolution of ∼100 μm using an autoradiographic technique. Under drought, the main zone of CH 4 assimilation shifted down the soil profile. Ammonium nitrate (NH 4 NO 3 ) and cattle urine reduced CH 4 assimilation in the top soil, but only when applied under drought, presumably because NH 4 + from fertilizers was not removed by plant uptake and nitrification under these conditions. Ecosystem-level CH 4 fluxes measured in the field did show no or only very small inhibitory effects, suggesting that deeper soil layers fully compensated for the reduction in top soil CH 4 assimilation. Our results indicate that the ecosystem-level CH 4 sink cannot be inferred from measurements of soil samples that do not reflect the spatial organization of soils (e.g. stratification of organisms, processes and mechanisms). The autoradiographic technique we have developed is suited to study methanotrophic activity in a relevant spatial context and does not rely on the genetic identity of the soil bacterial communities involved, thus ideally complementing DNA-based approaches.

Description: Ocean acidification (OA) refers to the increase in acidity (decrease in pH) of the ocean's surface waters resulting from oceanic uptake of atmospheric CO 2 . Mounting experimental evidence suggests that OA threatens numerous marine organisms, including reef-building corals. Coral recruitment is critical to the persistence and resilience of coral reefs and is regulated by several early life processes, including: larval availability (gamete production, fertilization, etc.), larval settlement, post-settlement growth and survival. Environmental factors that disrupt these early life processes can result in compromised or failed recruitment and profoundly affect future population dynamics. To evaluate the effects of OA on the sexual recruitment of corals, we tested larval metabolism, larval settlement, and post-settlement growth of the common Caribbean coral Porites astreoides at three p CO 2 levels: ambient seawater (380 μatm) and two p CO 2 scenarios that are projected to occur by the middle (560 μatm) and end (800 μatm) of the century. Our results show that larval metabolism is depressed by 27% and 63% at 560 and 800 μatm respectively compared to controls. Settlement was reduced by 42–45% at 560 μatm and 55–60% at 800 μatm, relative to controls. Results indicate that OA primarily affects settlement via indirect pathways, whereby acidified seawater alters the substrate community composition, limiting the availability of settlement cues. Post-settlement growth decreased by 16% and 35% at 560 and 800 μatm respectively, relative to controls. This study demonstrates that OA has the potential to negatively impact multiple early life history processes of P. astreoides and may contribute to substantial declines in sexual recruitment that are felt at the community and/or ecosystem scale.

Description: Productivity in boreal ecosystems is primarily limited by available soil nitrogen (N), and there is substantial interest in understanding whether deposition of anthropogenically derived reactive nitrogen (N r ) results in greater N availability to woody vegetation, which could result in greater carbon (C) sequestration. One factor that may limit the acquisition of N r by woody plants is the presence of bryophytes, which are a significant C and N pool, and a location where associative cyanobacterial N-fixation occurs. Using a replicated stand-scale N-addition experiment (five levels: 0, 3, 6, 12, and 50 kg N ha −1  yr −1 ; n =6) in the boreal zone of northern Sweden, we tested the hypothesis that sequestration of N r into bryophyte tissues, and down-regulation of N-fixation would attenuate N r inputs, and thereby limit anthropogenic N r acquisition by woody plants. Our data showed that N-fixation per unit moss mass and per unit area sharply decreased with increasing N addition. Additionally, the tissue N concentrations of P. schreberi increased and its biomass decreased with increasing N addition. This response to increasing N addition caused the P. schreberi N pool to be stable at all but the highest N addition rate, where it significantly decreased. The combined effects of changed N-fixation and Pleuorzium schreberi biomass N accounted for 56.7% of cumulative N r additions at the lowest N r addition rate, but only a minor fraction for all other treatments. This ‘bryophyte effect’ can in part explain why soil inorganic N availability and acquisition by woody plants (indicated by their δ 15 N signatures) remained unchanged up to N addition rates of 12 kg ha −1  yr −1 or greater. Finally, we demonstrate that approximately 71.8% of the boreal forest experiences N r deposition rates at or below 3 kg ha −1  yr −1 , suggesting that bryophytes likely limit woody plant acquisition of ambient anthropogenic N r inputs throughout a majority of the boreal forest.

Description: Climate models predict a dramatic increase in the annual frequency and severity of extreme weather events during the next century. Here we show that increases in the annual frequency of severe storms lead to a decrease in the diversity and complexity of food webs of giant kelp forests, one of the most productive habitats on Earth. We demonstrate this by linking natural variation in storms with measured changes in kelp forest food web structure in the Santa Barbara Channel using Structural Equations Modeling (SEM). We then match predictions from statistical models to results from a multi-year kelp removal experiment designed to simulate frequent large storms. Both SEM models and experiments agree: if large storms remain at their current annual frequency (roughly 1 major kelp-removing storm every 3.5 years), periodic storms help maintain the complexity of kelp forest food webs. However, if large storms increase in annual frequency and begin to occur year after year, kelp forest food webs become less diverse and complex as species go locally extinct. The loss of complexity occurs primarily due to decreases in the diversity and complexity of higher trophic levels. Our findings demonstrate that shifts in climate-driven disturbances that affect foundation species are likely to have impacts that cascade through entire ecosystems.

Description: Land-use change is a major driving factor for the balance of soil organic carbon (SOC) stocks and the global carbon cycle. The temporal dynamic of SOC after land-use change (LUC) is especially important in temperate systems with a long reaction time. On the basis of 95 compiled studies covering 322 sites in the temperate zone, carbon response functions were derived to model the temporal dynamic of SOC after five different LUC types (mean soil depth of 30±6 cm). Grassland establishment caused a long lasting carbon sink with a relative stock change of 128±23% and afforestation on former cropland a sink of 116±54%, 100 years after LUC (mean±95% confidence interval). No new equilibrium was reached within 120 years. In contrast, there was no SOC sink following afforestation of grasslands and 75% of all observations showed SOC losses, even after 100 years. Only in the forest floor there was carbon accumulation of 0.38±0.04 Mg ha −1  yr −1 in afforestations adding up to 38±4 Mg ha −1 labile carbon after 100 years. Carbon loss after deforestation (−32±20%) and grassland conversion to cropland (−36±5%), was rapid with a new SOC equilibrium being reached after 23 and 17 years, respectively. The change rate of SOC increased with temperature and precipitation but decreased with soil depth and clay content. Subsoil SOC changes followed the trend of the topsoil SOC changes but were smaller (25±5% of the total SOC changes) and with a high uncertainty due to a limited number of data sets. As a simple and robust model approach the developed carbon response functions provide an easily applicable tool to estimate SOC stock changes after LUC to improve greenhouse gas reporting in the framework of UNFCCC.

Description: Surface water temperatures in four lakes of the English Lake District ( T L ) are shown to be sensitive to climate change and a large-scale atmospheric phenomenon known as tropospheric Rossby wave breaking (RWB). RWB occurs frequently near the English Lake District, bringing warm and moist air, or cool and dry air, from distant sources. RWB case examples and composites are used to show three dimensional circulations and anomalies of near-surface temperature and humidity associated with the two types of RWB (anticyclonic and cyclonic). Statistical models of lake surface temperature are developed for each season using objectively identified variability patterns of anticyclonic and cyclonic RWB, along with an index of Northern Hemisphere annual mean surface temperature ( T NH ) to account for climate change. The statistical models, depending on season, account for 54–69% of T L variance. RWB alone contributes significantly during each season, accounting for 37–52% of T L variance after the effect of T NH is removed. RWB is a key physical mechanism underlying the North Atlantic Oscillation (NAO), a regional-scale weather-pattern that is frequently related to coherent lake properties. RWB may therefore be a more fundamental driver than the NAO in controlling interannual variation in the properties of lakes such as ice duration, metabolic rates, phenology, species composition and, via effects on stratification, underwater light-climate, nutrient-cycling and oxygen-depletion. Variation in other meteorological features that are linked to RWB, such as precipitation, may have additional effects. RWB is also likely to influence terrestrial and marine environments.