ALBERT

Notes: Abstract A young man adrift, I was rescued by Paul Gast, a college classmate, and sent off to Columbia's Lamont Geological Observatory as a summer intern. As it turns out, I am still there. During this 47-year sojourn, I have been a participant in the enormous expansion of the field of isotope geochemistry. I experienced the golden age when so many plums awaited picking that we, the pioneers, gorged ourselves with exciting discovery. Being at what is now called Lamont-Doherty Earth Observatory put me at the center of many of the developments that changed forever the Earth Sciences. It also made me part of the great challenge associated with the drive to replace the exploitative mode that characterized the Industrial Revolution with what is often referred to as the sustainable mode. In the following pages I recount my path from confused youth to the globe-encircling oceanic "conveyor belt."

Notes: Abstract The 1990s saw a resurgence in the windpower industry, with installed grid-connected capacity expanding more than five-fold between 1990 and 2000. Most of this increase occurred in Europe, where governmental policies aimed at developing domestic energy supplies and reducing pollutant emissions provided a sheltered market for renewable energy generation. The 1990s were also marked by a return to large, megawatt-sized wind turbines, a reduction and consolidation of wind turbine manufacturers, and increased interest in offshore windpower. This article reviews recent trends in the windpower industry, including some of the fundamental engineering principles of wind turbine design. Technological impediments and advances are discussed in the context of changes in the global electricity markets and environmental performance.

Notes: Abstract Civilization's advances during the twentieth century are closely bound with an unprecedented rise of energy consumption in general, and of hydrocarbons and electricity in particular. Substantial improvements of all key nineteenth-century energy techniques and introduction of new extraction and transportation means and new prime movers resulted in widespread diffusion of labor-saving and comfort-providing conversions and in substantially declining energy prices. Although modern societies could not exist without large and incessant flows of energy, there are no simple linear relationships between the inputs of fossil fuels and electricity and a nation's economic performance and social accomplishments. International comparisons show a variety of consumption patterns and a continuing large disparity between affluent and modernizing nations. The necessity of minimizing environmental impacts of energy use, particularly those with potentially worrisome global effects, is perhaps the greatest challenge resulting from the twentieth century's energy advances.

Notes: Abstract Phosphorus has a number of indispensable biochemical roles, but it does not have a rapid global cycle akin to the circulations of C or N. Natural mobilization of the element, a part of the grand geotectonic denudation-uplift cycle, is slow, and low solubility of phosphates and their rapid transformation to insoluble forms make the element commonly the growth-limiting nutrient, particularly in aquatic ecosystems. Human activities have intensified releases of P. By the year 2000 the global mobilization of the nutrient has roughly tripled compared to its natural flows: Increased soil erosion and runoff from fields, recycling of crop residues and manures, discharges of urban and industrial wastes, and above all, applications of inorganic fertilizers (15 million tonnes P/year) are the major causes of this increase. Global food production is now highly dependent on the continuing use of phosphates, which account for 50-60% of all P supply; although crops use the nutrient with relatively high efficiency, lost P that reaches water is commonly the main cause of eutrophication. This undesirable process affects fresh and ocean waters in many parts of the world. More efficient fertilization can lower nonpoint P losses. Although P in sewage can be effectively controlled, such measures are often not taken, and elevated P is common in treated wastewater whose N was lowered by denitrification. Long-term prospects of inorganic P supply and its environmental consequences remain a matter of concern.

Notes: Abstract Various applications using carbon dioxide (CO2) have developed within the last decade and, if current trends continue, the CO2 technology platform could emerge as the most commonly used solvent in the twenty-first century. An environmentally friendly platform that is wrapped in a successful business format with apparent implications for people and their communities is most likely to endure. Does the CO2 technology platform meet the criteria for becoming a sustainable enterprise? Utilizing CO2 as an alternative solvent in conventional processes has the potential to favorably impact the environment and our communities. There are, however, several barriers to adopting CO2-based applications. Several concepts as well as obstacles to adopting the carbon dioxide technology platform are highlighted in this chapter.

Notes: Abstract An ultimate limit on the extent that biomass fuels can be used to displace fossil transportation fuels, and their associated emissions of CO2, will be the land area available to produce the fuels and the efficiencies by which solar radiation can be converted to useable fuels. Currently, the Brazil cane-ethanol system captures 33% of the primary energy content in harvested cane in the form of ethanol. The US corn-ethanol system captures 54% of the primary energy of harvested corn kernels in the form of ethanol. If ethanol is used to substitute for gasoline, avoided fossil fuel CO2 emissions would equal those of the substituted amount minus fossil emissions incurred in producing the cane- or corn-ethanol. In this case, avoided emissions are estimated to be 29% of harvested cane and 14% of harvested corn primary energy. Unless these efficiencies are substantially improved, the displacement of CO2 emissions from transportation fuels in the United States is unlikely to reach 10% using domestic biofuels. Candidate technologies for improving these efficiencies include fermentation of cellulosic biomass and conversion of biomass into electricity, hydrogen, or alcohols for use in electric drive-train vehicles.

Notes: Abstract The first phase of promoting renewable energy in Europe is coming to an end. The timetable of the European Commission's Single Electricity Market (SEM) Directive has been the key recent driver of change within European energy and electricity markets. As mainland European countries have been forced to restructure their electricity industries and reappraise their renewable energy policies, they have been impressed by the results of the England and Wales Renewable Non-Fossil Fuel Obligation (NFFO). The NFFO is a mechanism for promoting renewable energy that has a competitive basis. However, the United Kingdom is in the process of creating a new policy. As new renewable energy policies have been discussed or put in place in mainland European countries, so these have influenced those of the United Kingdom. Renewable energy policies throughout Europe are converging. This paper analyzes the history behind these changes and underlines the lessons to be learned.

Notes: Abstract Geoengineering is the intentional large-scale manipulation of the environment, particularly manipulation that is intended to reduce undesired anthropogenic climate change. The post-war rise of climate and weather modification and the history of U.S. assessments of the CO2-climate problem is reviewed. Proposals to engineer the climate are shown to be an integral element of this history. Climate engineering is reviewed with an emphasis on recent developments, including low-mass space-based scattering systems for altering the planetary albedo, simulation of the climate's response to albedo modification, and new findings on iron fertilization in oceanic ecosystems. There is a continuum of human responses to the climate problem that vary in resemblance to hard geoengineering schemes such as space-based mirrors. The distinction between geoengineering and mitigation is therefore fuzzy. A definition is advanced that clarifies the distinction between geoengineering and industrial carbon management. Assessment of geoengineering is reviewed under various framings including economics, risk, politics, and environmental ethics. Finally, arguments are presented for the importance of explicit debate about the implications of countervailing measures such as geoengineering.

Notes: Abstract Industrial symbiosis, as part of the emerging field of industrial ecology, demands resolute attention to the flow of materials and energy through local and regional economies. Industrial symbiosis engages traditionally separate industries in a collective approach to competitive advantage involving physical exchange of materials, energy, water, and/or by-products. The keys to industrial symbiosis are collaboration and the synergistic possibilities offered by geographic proximity. This paper reviews the small industrial symbiosis literature and some antecedents, as well as early efforts to develop eco-industrial parks as concrete realizations of the industrial symbiosis concept. Review of the projects is organized around a taxonomy of five different material exchange types. Input-output matching, stakeholder processes, and materials budgeting appear to be useful tools in advancing eco-industrial park development. Evolutionary approaches to industrial symbosis are found to be important in creating the level of cooperation needed for multi-party exchanges.

Notes: Abstract Fossil fuels account for about 80% of energy consumption in Asia. Because of its abundance and easy recoverability, especially in India and China, coal will remain the fuel of choice in the foreseeable future. If current trends continue, sulfur dioxide emissions from Asia may soon equal the emissions from North America and Europe combined. These trends portend a variety of local, regional, and global environmental impacts. Acid rain damages human health, ecosystems, and built surfaces. Many ecosystems will be unable to absorb these increased acidic depositions, leading to irreversible ecosystem damage with far-reaching implications for health, forestry, agriculture, fisheries, and tourism. RAINS-ASIA is a scenario-generating tool used to estimate the extent of damages caused by acid rain and to review the costs and impacts of alternatives to provide a look into the future. Its use extends from national-, regional-, and city-scale evaluation and inputs for cost-effective options analyses, to international negotiations on transboundary pollution.

Notes: Abstract Over the past 25 years more than 20 major studies have examined the technological potential to improve the fuel economy of passenger cars and light trucks in the United States. The majority have used technology/cost analysis, a combination of analytical methods from the disciplines of economics and automotive engineering. In this review we describe the key elements of this methodology, discuss critical issues responsible for the often widely divergent estimates produced by different studies, review the history of this methodology's use, and present results from six recent assessments. Whereas early studies tended to confine their scope to the potential of proven technology over a 10-year time period, more recent studies have focused on advanced technologies, raising questions about how best to include the likelihood of technological change. The review concludes with recommendations for further research.

Notes: Abstract The notion of capacity development (CD) has been receiving increasing attention as a way to assist the South in its environmental management. Consequently, there has been an exploration of various facets of the capacity issue in the literature and an incorporation of CD in environmental programs of donor agencies. Yet, many of these discussions have remained rather broad, and efforts to develop environmental capacity have shown only limited success. Based on an examination of the capacity needs for environmental management in agriculture and industry, and for dealing with climate change, this review suggests that strengthening domestic capabilities for policy research and innovation as well as for managing technological change may be particularly critical to allow for adaptation of policies and technologies for local conditions and needs. Examination of innovative local experiments on environmental management in developing countries can also provide useful lessons on how to develop and utilize capacity that works under the constrained conditions often found in developing countries. Furthermore, it is important to stress that improving the environment in developing countries also requires capacity in the North to examine and reorient Northern policies that impact the environment, as well as capacity for the environment, in the poorer parts of the world. Ultimately, though, the development of sustainable and appropriate capacity for the environment will require not merely donor-driven programs but a systematic effort driven by Southern governments and organizations.

Notes: Abstract Water vapor is the dominant greenhouse gas, the most important gaseous source of infrared opacity in the atmosphere. As the concentrations of other greenhouse gases, particularly carbon dioxide, increase because of human activity, it is centrally important to predict how the water vapor distribution will be affected. To the extent that water vapor concentrations increase in a warmer world, the climatic effects of the other greenhouse gases will be amplified. Models of the Earth's climate indicate that this is an important positive feedback that increases the sensitivity of surface temperatures to carbon dioxide by nearly a factor of two when considered in isolation from other feedbacks, and possibly by as much as a factor of three or more when interactions with other feedbacks are considered. Critics of this consensus have attempted to provide reasons why modeling results are overestimating the strength of this feedback. Our uncertainty concerning climate sensitivity is disturbing. The range most often quoted for the equilibrium global mean surface temperature response to a doubling of CO2 concentrations in the atmosphere is 1.5oC to 4.5oC. If the Earth lies near the upper bound of this sensitivity range, climate changes in the twenty-first century will be profound. The range in sensitivity is primarily due to differing assumptions about how the Earth's cloud distribution is maintained; all the models on which these estimates are based possess strong water vapor feedback. If this feedback is, in fact, substantially weaker than predicted in current models, sensitivities in the upper half of this range would be much less likely, a conclusion that would clearly have important policy implications. In this review, we describe the background behind the prevailing view on water vapor feedback and some of the arguments raised by its critics, and attempt to explain why these arguments have not modified the consensus within the climate research community.

Notes: Abstract Theoretical considerations and empirical data suggest that existing technologies and procedures can improve indoor environments in a manner that significantly increases productivity and health. The existing literature contains moderate to strong evidence that characteristics of buildings and indoor environments significantly influence rates of communicable respiratory illness, allergy and asthma symptoms, sick building symptoms, and worker performance. Whereas there is considerable uncertainty in the estimates of the magnitudes of productivity gains that may be obtained by providing better indoor environments, the projected gains are very large. For the United States, the estimated potential annual savings and productivity gains are $6 to $14 billion from reduced respiratory disease, $1 to $4 billion from reduced allergies and asthma, $10 to $30 billion from reduced sick building syndrome symptoms, and $20 to $160 billion from direct improvements in worker performance that are unrelated to health. Productivity gains that are quantified and demonstrated could serve as a strong stimulus for energy efficiency measures that simultaneously improve the indoor environment.

Notes: Abstract Low environmental damage is one of the main justifications for continued efforts to reduce energy consumption and to shift to cleaner sources such as solar energy, especially now that supply security has slipped from public consciousness. In recent years there has been much progress in the analysis of environmental damages, in particular thanks to the ExternE (External Costs of Energy) Project of the European Commission. This paper presents a summary of the methodology and key results for the external costs of the major energy technologies. Even though the uncertainties are large, the results provide substantial evidence that the classic air pollutants (particles, NOx and SOx) from fossil fuels impose significant public health costs, comparable to the cost of global warming from CO2 emissions.

Notes: Abstract Current guidelines for green buildings are cursory and inadequate for specifying materials and designing ventilation systems to ensure a healthful indoor environment, i.e. a "healthy building," by design. Public perception, cultural preferences, litigation trends, current codes and regulations, and rapid introduction of new building materials and commercial products, as well as the prevailing design-build practices, pose challenges to systems integration in the design, construction and operation phases of modern buildings. We are on the verge of a paradigm shift in ventilation design thinking. In the past, thermal properties of air within a zone determined heating, ventilating, and air-conditioning specifications. In the future, occupant-specific and highly responsive systems will become the norm. Natural ventilation, displacement ventilation, and microzoning with subfloor plenums, along with the use of point-of-source heat control and point-of-use sensors, will evolve to create a "smart," responsive ventilation-building dynamic system. Advanced ventilation design tools such as the modeling of computational fluid dynamics (CFD) will be used routinely. CFD will be integrated into air quality and risk assessment models.

Notes: Abstract Indian megacities are among the most polluted in the world. Air concentrations of a number of air pollutants are much higher than levels recommended by the World Health Organization. In this paper, we focus on Mumbai and Delhi to characterize salient issues in health risks from particulate air (PM10) pollution in Indian cities. We perform a synthesis of the literature for all elements of the causal chain of health risks-sources, exposure, and health effects-and provide estimates of source strengths, exposure levels, and health risks from air pollution in Indian cities. We also analyze the factors that lead to uncertainty in these quantities and provide an overall assessment of the state of scientific knowledge on air pollution in urban India.

Notes: Abstract This paper reviews the available data and models on energy and material flows through the world's 25 largest cities. Throughput is categorized as stored, transformed, or passive for the major flow modes. The aggregate, fuel, food, water, and air cycles are all examined. Emphasis is placed on atmospheric pathways because the data are abundant. Relevant models of urban energy and material flows, demography, and atmospheric chemistry are discussed. Earth system-level loops from cities to neighboring ecosystems are identified. Megacities are somewhat independent of their immediate environment for food, fuel, and aggregate inputs, but all are constrained by their regional environment for supplying water and absorbing wastes. We elaborate on analogies with biological metabolism and ecosystem succession as useful conceptual frameworks for addressing urban ecological problems. We conclude that whereas data are numerous for some individual cities, cross-cutting compilations are lacking in biogeochemical analysis and modeling. Synthesis of the existing information will be a crucial first step. Cross-cutting field research and integrated, multidisciplinary simulations will be necessary.

Notes: Abstract It is commonly assumed that biomass fuel cycles based on renewable harvesting of wood or agricultural wastes are greenhouse-gas (GHG) neutral because the combusted carbon in the form of CO2 is soon taken up by regrowing vegetation. Thus, the two fifths or more of the world's households relying on such fuels are generally not thought to play a significant role in GHG emissions, except where the wood or other biomass they use is not harvested renewably. This review examines this assumption using an emissions database of CO2, CO, CH4, NMHC, N2O, and total suspended particulate emissions from a range of household stoves in common use in India using six biomass fuels, kerosene, liquefied petroleum gas, and biogas. Because typical biomass stoves are thermally inefficient and divert substantial fuel carbon to products of incomplete combustion, their global warming commitment (GWC) per meal is high. Depending on time horizons and which GHGs are measured, the GWC of a meal cooked on a biomass stove can actually exceed that of the fossil fuels, even if based on renewably harvested fuel. Biogas, being based on a renewable fuel and, because it is a gas, being combusted with high efficiency in simple devices, has by far the lowest GWC emitted at the stove per meal and is indicative of the advantage that upgraded fuels made from biomass have in moving toward sustainable development goals. There are a number of policy implications of this work, including revelation of a range of win-win opportunities for international investment in rural energy development that would achieve cost-effective GHG reduction as well as substantial local benefits.

Notes: Abstract We assess the environmental health impact and policy implications of the widespread addition of methyl tert-butyl ether (MTBE) as a chemical that is used as an oxygenate to much of the gasoline supply in the United States. Initial concerns about short-term and long-term adverse health consequences following the substantial increase in MTBE use in the winter of 1992-1993 have been supplemented by the discovery in 1996 of what is now relatively widespread contamination of groundwater. We identify 14 governmental initiatives during the 10-year period 1989-1999 in which the potential adverse consequences of MTBE were considered and a nearly identical research agenda was proposed. The lessons from the ongoing MTBE episode show that: (a) research should precede rather than follow environmental health policy decisions; (b) the extent of potential human and environmental exposure should be an important criterion in determining the amount of information needed before making an environmental policy decision; (c) a better understanding of nonspecific human symptoms associated with environmental exposures is needed; (d) the boundaries between the US Environmental Protection Agency program offices should be as porous as the boundaries between environmental media; (e) the US Environmental Protection Agency needs to focus more on public health rather than on legal approaches to environmental management; (f) it is more difficult to remove a chemical once it is in commerce than it is to prevent its use; (g) resolution of uncertainty is best accomplished through research rather than through repetitive review; and (h) better tools are needed to evaluate risk/risk trade-offs. The ongoing replacement of MTBE by other, less well studied oxygenates such as tertiary amyl methyl ether indicates that these environmental public policy lessons have not been learned.

Notes: Abstract Meeting the growing demand for personal mobility and transport of goods in a sustainable way presents a wide range of interrelated engineering and public policy challenges. This chapter reviews some of the technical options being developed for mitigating the local and global environmental impact of road vehicles, made possible using developments in the materials and combustion sciences, sensor technologies, catalysis, and information processing. Although the improved technical performance of these options can be quantified, the likelihood of commercial success is harder to predict. This review considers factors that may support the adoption of innovative vehicle technologies, recognizing that the ubiquity of existing solutions and infrastructures will make any change process complex.

Notes: We investigated how light and CO2 levels interact to influence growth, phenology, and the physiological processes involved in leaf senescence in red oak (Quercus rubra) seedlings. We grew plants in high and low light and in elevated and ambient CO2. At the end of three years of growth, shade plants showed greater biomass enhancement under elevated CO2 than sun plants. We attribute this difference to an increase in leaf area ratio (LAR) in shade plants relative to sun plants, as well as to an ontogenetic effect: as plants increased in size, the LAR declined concomitant with a decline in biomass enhancement under elevated CO2Elevated CO2 prolonged the carbon gain capacity of shade-grown plants during autumnal senescence, thus increasing their functional leaf lifespan. The prolongation of carbon assimilation, however, did not account for the increased growth enhancement in shade plants under elevated CO2. Elevated CO2 did not significantly alter leaf phenology. Nitrogen concentrations in both green and senesced leaves were lower under elevated CO2 and declined more rapidly in sun leaves than in shade leaves. Similar to nitrogen concentration, the initial slope of A/Ci curves indicated that Rubisco activity declined more rapidly in sun plants than in shade plants, particularly under elevated CO2. Absolute levels of chlorophyll were affected by the interaction of CO2 and light, and chlorophyll content declined to a minimal level in sun plants sooner than in shade plants. These declines in N concentration, in the initial slope of A/Ci curves, and in chlorophyll content were consistent with declining photosynthesis, such that elevated CO2 accelerated senescence in sun plants and prolonged leaf function in shade plants. These results have implications for the carbon economy of seedlings and the regeneration of red oak under global change conditions.

Notes: Plant phenology, the study of seasonal plant activity driven by environmental factors, has found a renewal in the context of global climate change. Phenological events, such as leaf unfolding, exert strong control over seasonal exchanges of matter and energy between the land surface and the atmosphere. Phenological models that simulate the start of the growing season should be efficient tools to predict vegetation responses to climatic changes and related changes in energy balance. Species-specific phenological models developed in the eighties have not been used for global-scale predictions because their predictions were inaccurate in external conditions. Recent advances in phenology modelling at the species level suggest that prediction at a large scale may now be possible. In the present study, we tested the performance of species-specific phenological models in time and space, looking at their ability (i) to predict regional phenology when previously fitted at a local scale, and (ii) to predict phenological trends, linked to climate changes, observed over a long-term. For that task we used an historical phenological dataset from Ohio from the late ninetieth century and an airborne pollen dataset from Ontario, Québec and Maryland from the late twentieth century. The results show that the species-specific phenological models used in this study were able to predict regional phenology even though they were fitted locally. The reconstruction of a phenological time series over the twentieth century showed a significant advancement of 0.2 days per year in the date of flowering of Ulmus americana, but very weak trends for Fraxinus americana and Quercus velutina.

Notes: Upland rice (Oryza sativa L.) was grown at both ambient (350 μmol mol−1) and elevated (700 μmol mol−1) CO2 in either the presence or absence of the root hemi-parasitic angiosperm Striga hermonthica (Del) Benth. Elevated CO2 alleviated the impact of the parasite on host growth: biomass of infected rice grown at ambient CO2 was 35% that of uninfected, control plants, while at elevated CO2, biomass of infected plants was 73% that of controls. This amelioration occurred despite the fact that O. sativa grown at elevated CO2 supported both greater numbers and a higher biomass of parasites per host than plants grown at ambient CO2. The impact of infection on host leaf area, leaf mass, root mass and reproductive tissue mass was significantly lower in plants grown at elevated as compared with ambient CO2. There were significant CO2 and Striga effects on photosynthetic metabolism and instantaneous water-use efficiency of O. sativa. The response of photosynthesis to internal [CO2] (A/Ci curves) indicated that, at 45 days after sowing (DAS), prior to emergence of the parasites, uninfected plants grown at elevated CO2 had significantly lower CO2 saturated rates of photosynthesis, carboxylation efficiencies and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) contents than uninfected, ambient CO2-grown O. sativa. In contrast, infection with S. hermonthica prevented down-regulation of photosynthesis in O. sativa grown at elevated CO2, but had no impact on photosynthesis of hosts grown at ambient CO2. At 76 DAS (after parasites had emerged), however, infected plants grown at both elevated and ambient CO2 had lower carboxylation efficiencies and Rubisco contents than uninfected O. sativa grown at ambient CO2. The reductions in carboxylation efficiency (and Rubisco content) were accompanied by similar reductions in nitrogen concentration of O. sativa leaves, both before and after parasite emergence. There were no significant CO2 or infection effects on the concentrations of soluble sugars in leaves of O. sativa, but starch concentration was significantly lower in infected plants at both CO2 concentrations. These results demonstrate that elevated CO2 concentrations can alleviate the impact of infection with Striga on the growth of C3 hosts such as rice and also that infection can delay the onset of photosynthetic down-regulation in rice grown at elevated CO2.

Notes: A closed-dynamic-chamber system (CDCS) was used to measure the spatial and seasonal variability of the soil CO2 efflux (Fs) in beech and in Douglas fir patches of the Vielsalm forest (Belgium). First the difference between natural and measured soil CO2 efflux induced by the presence of the CDCS was studied. The impact on the measurements of the pressure difference between the outside (natural condition) and the inside of the chamber was found to be small (0.4%). The influence of wind disturbance in the closed chamber was tested by comparison with an open-chamber system characterized by a different wind distribution. A very good correlation between the two systems was found (r2 = 0.99) but the open system yielded slightly lower fluxes than the closed one (slope = 0.88 ± 0.05). A measurement procedure has been developed to minimize the effect of the other sources of perturbation.The spatial and seasonal evolution of the soil CO2 efflux was obtained by performing regular measurements on 29 spots in the beech patch over a period of 12 months and on 24 spots in the Douglas fir patch over 8 months. For each spot, the experimental relationship between Fs and soil temperature was compared with the fitted line for an Arrhenius relationship with a soil temperature-dependent activation energy.Soil temperature explains 73% of the seasonal variation for all the data. The spatial average of the soil CO2 efflux at 10 °C (Fs10) in the beech patch is 2.57 ± 0.41 μmol m−2 s−1, approximately twice the average in the Douglas fir patch recorded at 1.42 ± 0.22 μmol m−2 s−1.The litter fall analysis seems to indicate that soil organic matter quality and quantity may be one the reasons for this difference. Finally the annual soil CO2 efflux was calculated for the beech and Douglas fir patches (870 ± 140 and 438 ± 68 gC m−2 y−1, respectively). The beech value would represent 92 ± 15% of the annual ecosystem respiration estimated from the eddy covariance measurements.

Notes: Plants grown at elevated pCO2 often fail to sustain the initial stimulation of net CO2 uptake rate (A). This reduced, acclimated, stimulation of A often occurs concomitantly with a reduction in the maximum carboxylation velocity (Vc,max) of Rubisco. To investigate this relationship we used the Farquhar model of C3 photosynthesis to predict the minimum Vc,max capable of supporting the acclimated stimulation in A observed at elevated pCO2. For a wide range of species grown at elevated pCO2 under contrasting conditions we found a strong correlation between observed and predicted values of Vc,max. This exercise mechanistically and quantitatively demonstrated that the observed acclimated stimulation of A and the simultaneous decrease in Vc,max observed at elevated pCO2 is mechanistically consistent. With the exception of plants grown at a high elevated pCO2 (〉 90 Pa), which show evidence of an excess investment in Rubisco, the failure to maintain the initial stimulation of A is almost entirely attributable to the decrease in Vc,max and investment in Rubisco is coupled to requirements.

Notes: Annual carbon budgets of ecosystems are central to our understanding of the biotic control of atmospheric composition, but they are not available under elevated CO2 for most vegetation types. Using gas exchange techniques, we assessed carbon fluxes of four early successional Mediterranean model communities, consisting of grasses, legumes and composites. The assemblages were grown on the same monoliths for three consecutive years in greenhouses tracking field conditions except for CO2 maintained at ambient (370 μmol mol−1) or elevated (700 μmol mol−1) concentration.During the third year of study, CO2 enrichment consistently shifted the annual carbon balance towards lower efflux, with displacements between 4.3 and 26.2 mol m−2 y−1 (one assemblage became a net CO2 sink, another just reached equilibrium, and the remaining two remained as a CO2 source). At least 50% of the shift under elevated CO2 originated from a decrease in belowground respiration. This indicates that, during this year, CO2 enrichment did not predominantly enhance C-cycling, but on the contrary inhibited root respiration or microbial C-utilization.Although elevated-CO2-grown systems acted as a net CO2 sink during a longer period of the year (4–7 months) compared with ambient-CO2-grown systems (3–3.5 months), gross canopy photosynthesis was modified only to a limited extent (between −5.9 and + 14.8%). Interaction between the carbon and the water cycle was apparently responsible for this weak stimulation. In particular, reduced evapotranspiration under elevated CO2 coincided with inhibited canopy photosynthesis in early spring, most likely resulting from water saturation of the soil. In addition, only the earliest-planted assemblages had an increased gross canopy photosynthesis during late autumn and early winter. This suggests that a longer summer drought, by delaying the establishment of such an annual type of vegetation, would reduce the positive impact of elevated CO2 on productivity. Water regime appears to strongly govern the influence of CO2 on the carbon fluxes in Mediterranean ecosystems with annual herbaceous vegetation.

Notes: A combined stomatal–photosynthesis model was extended to simulate the effects of ozone exposure on leaf photosynthesis and leaf duration in relation to CO2. We assume that ozone has a short-term and a long-term effect on the Rubisco-limited rate of photosynthesis, Ac. Elevated CO2 counteracts ozone damage via stomatal closure. Ozone is detoxified at uptake rates below a threshold value above which Ac decreases linearly with the rate of ozone uptake. Reduction in Ac is transient and depends on leaf age. Leaf duration decreases depending on accumulated ozone uptake. This approach is introduced into the mechanistic crop simulation model AFRCWHEAT2. The derived model, AFRCWHEAT2-O3, is used to test the capability of these assumptions to explain responses at the plant and crop level.Simulations of short-term and long-term responses of leaf photosynthesis, leaf duration and plant and crop growth to ozone exposure in response to CO2 are analysed and compared with experimental data derived from the literature. The model successfully reproduced published responses of leaf photosynthesis, leaf duration, radiation use efficiency and final biomass of wheat to elevated ozone and CO2. However, simulations were unsatisfactory for cumulative radiation interception which had some impact on the accuracy of predictions of final biomass. There were responses of leaf-area index to CO2 and ozone as a result of effects on tillering which were not accounted for in the present model. We suggest that some model assumptions need to be tested, or analysed further to improve the mechanistic understanding of the combined effects of changes in ozone and CO2 concentrations on leaf photosynthesis and senescence. We conclude that research is particularly needed to improve the understanding of leaf-area dynamics in response to ozone exposure and elevated CO2.

Notes: The growth and chemical composition of most plants are influenced by elevated CO2, but accompanying effects on soil organic matter pools and mineralization are less clearly defined, partly because of the short-term nature of most studies. Herein we describe soil properties from a naturally occurring cold CO2 spring (Hakanoa) in Northland, New Zealand, at which the surrounding vegetation has been exposed to elevated CO2 for at least several decades. The mean annual temperature at this site is ≈ 15.5 °C and rainfall ≈ 1550 mm. The site was unfertilized and ungrazed, with a vegetation of mainly C3 and C4 grasses, and had moderate levels of ‘available’ P. Two soils were present − a gley soil and an organic soil – but only the gley soil is examined here. Average atmospheric CO2 concentrations at 17 sampling locations in the gley soil area ranged from 372 to 670 ppmv.In samples at 0–5 cm depth, pH averaged 5.4; average values for organic C were 150 g, total N 11 g, microbial C 3.50 g, and microbial N 0.65 g kg−1, respectively. Under standardized moisture conditions at 25 °C, average rates of CO2-C production (7–14 days) were 5.4 mg kg−1 h−1 and of net mineral-N production (14 −42 days) 0.40 mg kg−1 h−1. These properties were all correlated positively and significantly (P 〈 0.10) with atmospheric CO2 concentrations, but not with soil moisture (except for CO2-C production) or with clay content; they were, however, correlated negatively and mainly significantly with soil pH. In spite of uncertainties associated with the uncontrolled environment of naturally occurring springs, we conclude that storage of C and N can increase under prolonged exposure to elevated CO2, and may include an appreciable labile fraction in mineral soil with an adequate nutrient supply.

Notes: A nonequilibrium, dynamic, global vegetation model, Hybrid v4.1, with a subdaily timestep, was driven by increasing CO2 and transient climate output from the UK Hadley Centre GCM (HadCM2) with simulated daily and interannual variability. Three IPCC emission scenarios were used: (i) IS92a, giving 790 ppm CO2 by 2100, (ii) CO2 stabilization at 750 ppm by 2225, and (iii) CO2 stabilization at 550 ppm by 2150. Land use and future N deposition were not included. In the IS92a scenario, boreal and tropical lands warmed 4.5 °C by 2100 with rainfall decreased in parts of the tropics, where temperatures increased over 6 °C in some years and vapour pressure deficits (VPD) doubled. Stabilization at 750 ppm CO2 delayed these changes by about 100 years while stabilization at 550 ppm limited the rise in global land surface temperature to 2.5 °C and lessened the appearance of relatively hot, dry areas in the tropics.Present-day global predictions were 645 PgC in vegetation, 1190 PgC in soils, a mean carbon residence time of 40 years, NPP 47 PgC y−1 and NEP (the terrestrial sink) about 1 PgC y−1, distributed at both high and tropical latitudes. With IS92a emissions, the high latitude sink increased to the year 2100, as forest NPP accelerated and forest vegetation carbon stocks increased. The tropics became a source of CO2 as forest dieback occurred in relatively hot, dry areas in 2060–2080. High VPDs and temperatures reduced NPP in tropical forests, primarily by reducing stomatal conductance and increasing maintenance respiration. Global NEP peaked at 3–4 PgC y−1 in 2020–2050 and then decreased abruptly to near zero by 2100 as the tropical source offset the high-latitude sink. The pattern of change in NEP was similar with CO2 stabilization at 750 ppm, but was delayed by about 100 years and with a less abrupt collapse in global NEP. CO2 stabilization at 550 ppm prevented sustained tropical forest dieback and enabled recovery to occur in favourable years, while maintaining a similar time course of global NEP as occurred with 750 ppm stabilization. By lessening dieback, stabilization increased the fraction of carbon emissions taken up by the land. Comparable studies and other evidence are discussed: climate-induced tropical forest dieback is considered a plausible risk of following an unmitigated emissions scenario.

Notes: Increased atmospheric carbon dioxide supply is predicted to alter plant growth and biomass allocation patterns. It is not clear whether changes in biomass allocation reflect optimal partitioning or whether they are a direct effect of increased growth rates. Plasticity in growth and biomass allocation patterns was investigated at two concentrations of CO2 ([CO2]) and at limiting and nonlimiting nutrient levels for four fast- growing old-field annual species. Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, and Polygonum pensylvanicum were grown from seed in controlled growth chamber conditions at current (350 μmol mol−1, ambient) and future- predicted (700 μmol mol−1, elevated) CO2 levels. Frequent harvests were used to determine growth and biomass allocation responses of these plants throughout vegetative development. Under nonlimiting nutrient conditions, whole plant growth was increased greatly under elevated [CO2] for three C3 species and moderately increased for a C4 species (Amaranthus). No significant increases in whole plant growth were observed under limiting nutrient conditions. Plants grown in elevated [CO2] had lower or unchanged root:shoot ratios, contrary to what would be expected by optimal partitioning theory. These differences disappeared when allometric plots of the same data were analysed, indicating that CO2-induced differences in root:shoot allocation were a consequence of accelerated growth and development rates. Allocation to leaf area was unaffected by atmospheric [CO2] for these species. The general lack of biomass allocation responses to [CO2] availability is in stark contrast with known responses of these species to light and nutrient gradients. We conclude that biomass allocation responses to elevated atmospheric [CO2] are not consistent with optimal partitioning predictions.

Notes: Few studies have investigated how tree species grown under elevated CO2 and elevated temperature alter the performance of leaf-feeding insects. The indirect effects of an elevated CO2 concentration and temperature on leaf phytochemistry, along with potential direct effects on insect growth and consumption, may independently or interactively affect insects. To investigate this, we bagged larvae of the gypsy moth on leaves of red and sugar maple growing in open-top chambers in four CO2/temperature treatment combinations: (i) ambient temperature, ambient CO2; (ii) ambient temperature, elevated CO2 (+ 300 μL L−1 CO2); (iii) elevated temperature (+ 3.5°C), ambient CO2; and (iv) elevated temperature, elevated CO2. For both tree species, leaves grown at elevated CO2 concentration were significantly reduced in leaf nitrogen concentration and increased in C: N ratio, while neither temperature nor its interaction with CO2 concentration had any effect. Depending on the tree species, leaf water content declined (red maple) and carbon-based phenolics increased (sugar maple) on plants grown in an enriched CO2 atmosphere. The only observed effect of elevated temperature on leaf phytochemistry was a reduction in leaf water content of sugar maple leaves. Gypsy moth larval responses were dependent on tree species. Larvae feeding on elevated CO2-grown red maple leaves had reduced growth, while temperature had no effect on the growth or consumption of larvae. No significant effects of either temperature or CO2 concentration were observed for larvae feeding on sugar maple leaves. Our data demonstrate strong effects of CO2 enrichment on leaf phytochemical constituents important to folivorous insects, while an elevated temperature largely has little effect. We conclude that alterations in leaf chemistry due to an elevated CO2 atmosphere are more important in this plant–folivorous insect system than either the direct short-term effects of temperature on insect performance or its indirect effects on leaf chemistry.

Notes: Long-term data on water temperature, phytoplankton biovolume, Bosmina and Daphnia abundance and the timing of the clear-water phase were compared and analysed with respect to the influence of the North Atlantic Oscillation (NAO) in two strongly contrasting lakes in central Europe. In small, shallow, hypertrophic Müggelsee, spring water temperatures and Daphnia abundance both increased more rapidly than in large, deep, meso/oligotrophic Lake Constance. Because of this, the clear-water phase commenced approximately three weeks earlier in Müggelsee than in Lake Constance. In Müggelsee, the phytoplankton biovolume during late winter/early spring was related to the NAO index. In Lake Constance, where phytoplankton growth was inhibited by intense downward mixing during all years studied, this was not the case. However, in both lakes, interannual variability in water temperature, in Daphnia spring population dynamics and in the timing of the clear-water phase, were all related to the interannual variability of the NAO index. The Daphnia spring population dynamics and the timing of the clear-water phase appear to be synchronized by the NAO despite large differences between the lakes in morphometry, trophic status and flushing and mixis regimes, and despite the great distance between the lakes (∼700 km). This suggests that a great variety of lakes in central Europe may possibly have exhibited similar interannual variability during the last 20 years.

Notes: A field experiment was established to examine the effects of temperature and moisture modifications on the nematode fauna of a semiarid grassland. Several combinations of drying, wetting, warming and cooling were applied to plots and compared with untreated control plots. The experiment was performed from July to October 1996. A significant shift was observed in the structure of the nematode fauna between late summer and early autumn. This shift was manifested in the disappearance of four rare genera; Ecumenicus, Eucephalobus, Paraphelenchus and Pungentus. A significant decrease was found in the density of Acrobeles, Aphelenchoides, Ditylenchus and Prismatolaimus; in addition there was a significant increase in the density of Cephalobus, Helicotylenchus, Paratylenchus and Tylenchorhynchus. Community structural change was represented by an initial decrease in nematode generic richness of 30–50%, and in a statistically significant decrease of nematode diversity in the control and all treated plots. Thereafter, emergence of a new community was demonstrated. Data show that temperature manipulation was the main factor to influence nematode diversity, Maturity Index, and Plant Parasite Index. However, nematode population density was influenced predominantly by the soil moisture content. Coenological analysis of soil nematode fauna appears to be a useful tool for the biological monitoring of the effects of global change on semiarid grasslands.

Notes: We investigated the connection between plant species diversity and climate by using a process-based, generic plant model. Different ‘species' were simulated by different values for certain growth-related model parameters. Subsequently, a wide range of values were tested in the framework of a ‘Monte Carlo' simulation for success; that is, the capability of each plant with these parameter combinations to reproduce itself during its lifetime. The range of successful parameter combinations approximated species diversity. This method was applied to a global grid, using daily atmospheric forcing from a climate model simulation. The computed distribution of plant ‘species' diversity compares very well with the observed, global-scale distribution of species diversity, reproducing the majority of ‘hot spot' areas of biodiversity. A sensitivity analysis revealed that the predicted pattern is very robust against changes of fixed model parameters. Analysis of the climatic forcing and of two additional sensitivity simulations demonstrated that the crucial factor leading to this distribution of diversity is the early stage of a plant's life when water availability is highly coupled to the variability in precipitation because in this stage root-zone storage of water is small. We used cluster analysis in order to extract common sets of species parameters, mean plant properties and biogeographic regions (biomes) from the model output. The successful ‘species' cannot be grouped into typical parameter combinations, which define the plant's functioning. However, the mean simulated plant properties, such as lifetime and growth, can be grouped into a few characteristic plant ‘prototypes', ranging from short-lived, fast growing plants, similar to grasses, to long-lived, slow growing plants, similar to trees. The classification of regions with respect to similar combinations of successful ‘species' yields a distribution of biomes similar to the observed distribution. Each biome has typical levels of climatic constraints, expressed for instance by the number of ‘rainy days' and ‘warm days'. The less the number of days favourable for growth, the greater the level of constraints and the less the ‘species' diversity. These results suggest that climate as a fundamental constraint can explain much of the global scale, observed distribution of plant species diversity.

Notes: An empirical model of nitrous oxide emission from agricultural soils has been developed. It is based on the relationship between N2O and three soil parameters – soil mineral N (ammonium plus nitrate) content in the topsoil, soil water-filled pore space and soil temperature – determined in a study on a fertilized grassland in 1992 and 1993. The model gave a satisfactory prediction of seasonal fluxes in other seasons when fluxes were much higher, and also from other grassland sites and from cereal and oilseed rape crops, over a wide flux range (〈 1 to 〉 20 kg N2O-N ha−1 y−1). However, the model underestimated emissions from potato and broccoli crops; possible reasons for this are discussed. This modelling approach, based as it is on well-established and widely used soil measurements, has the potential to provide flux estimates from a much wider range of agricultural sites than would be possible by direct measurement of N2O emissions.

Notes: Elevated atmospheric CO2 concentration may result in increased below-ground carbon allocation by trees, thereby altering soil carbon cycling. Seasonal estimates of soil surface carbon flux were made to determine whether carbon losses from Pinus radiata trees growing at elevated CO2 concentration were higher than those at ambient CO2 concentration, and whether this was related to increased fine root growth.Monthly soil surface carbon flux density (f) measurements were made on plots with trees growing at ambient (350) and elevated (650 μmol mol−1) CO2 concentration in large open-top chambers. Prior to planting the soil carbon concentration (0.1%) and f (0.28 μmol m−2 s−1 at 15 °C) were low. A function describing the radial pattern of f with distance from tree stems was used to estimate the annual carbon flux from tree plots. Seasonal estimates of fine root production were made from minirhizotrons and the radial distribution of roots compared with radial measurements of f. A one-dimensional gas diffusion model was used to estimate f from soil CO2 concentrations at four depths.For the second year of growth, the annual carbon flux from the plots was 1671 g y−1 and 1895 g y−1 at ambient and elevated CO2 concentrations, respectively, although this was not a significant difference. Higher f at elevated CO2 concentration was largely explained by increased fine root biomass. Fine root biomass and stem production were both positively related to f. Both root length density and f declined exponentially with distance from the stem, and had similar length scales. Diurnal changes in f were largely explained by changes in soil temperature at a depth of 0.05 m.Ignoring the change of f with increasing distance from tree stems when scaling to a unit ground area basis from measurements with individual trees could result in under- or overestimates of soil-surface carbon fluxes, especially in young stands when fine roots are unevenly distributed.

Notes: The influence of seasonal to interannual climate variations on cellulose hydrogen isotopic composition (δD) was assessed by analysing tree rings and needles of piñon pine (Pinus edulis and P. monophylla). Sites spanned a gradient of decreasing summer precipitation, from New Mexico to Arizona to Nevada. Tree rings were divided into earlywood, latewood and whole-year increments, and annual cohorts of needles were collected. The study period (1989–96) included two La Niña events (1989, 1996) and a prolonged El Niño event (1991–95). Winter and spring moisture conditions were strongly related to October–March Southern Oscillation Index (SOI) in New Mexico and Arizona, with above-average precipitation occurring in El Niño years. Wood δD values at these sites were correlated with winter and spring moisture conditions. Needle δD values were correlated with summer moisture conditions in New Mexico and with winter moisture and SOI in Arizona. Low cellulose δD values observed from 1991 to 1993 in both wood and needles occurred during wet El Niño years, whereas high δD values in needles were present during the dry, La Niña years of 1989 and 1996. North-eastern Nevada does not receive precipitation anomalies related to ENSO, and thus cellulose δD values did not reflect the ENSO pattern observed at the other sites. Cellulose δD values were strongly, inversely correlated with relative humidity variations at all sites, as predicted by a mechanistic model. Contrary to predictions from the same model and observations from more mesic areas, time series of cellulose δD values were not directly correlated with interannual or seasonal variations in precipitation δD values or temperature at any of the sites. On a regional basis, however, mean δD values in needles and wood were correlated with mean annual temperature and δD values of precipitation. This suggests that temporal averaging may bias relationships between biological systems and climate.

Notes: Studies have suggested that more carbon is fixed due to a large increase in photosynthesis in plant–soil systems exposed to elevated CO2 than could subsequently be found in plant biomass and soils –- the locally missing carbon phenomenon. To further understand this phenomenon, an experiment was carried out using EcoCELLs which are open-flow, mass-balance systems at the mesocosm scale. Naturally occurring 13C tracers were also used to separately measure plant-derived carbon and soil-derived carbon. The experiment included two EcoCELLs, one under ambient atmospheric CO2 and the other under elevated CO2 (ambient plus 350 μL L− 1). By matching carbon fluxes with carbon pools, the issue of locally missing carbon was investigated. Flux-based net primary production (NPPf) was similar to pool-based primary production (NPPp) under ambient CO2, and the discrepancy between the two carbon budgets (12 g C m− 2, or 4% of NPPf) was less than measurement errors. Therefore, virtually all carbon entering the system under ambient CO2 was accounted for at the end of the experiment. Under elevated CO2, however, the amount of NPPf was much higher than NPPp, resulting in missing carbon of approximately 80 g C m− 2 or 19% of NPPf which was much higher than measurement errors. This was additional to the 96% increase in rhizosphere respiration and the 50% increase in root growth, two important components of locally missing carbon. The mystery of locally missing carbon under elevated CO2 remains to be further investigated. Volatile organic carbon, carbon loss due to root washing, and measurement errors are discussed as some of the potential contributing factors.

Notes: Tree transpiration was measured in 28, 67, 204 and 383-y-old uniform stands and in a multicohort stand (140–430 y) of Pinus sylvestris ssp. sibirica Lebed. in Central Siberia during August 1995. In addition transpiration of three codominant trees was monitored for two years in a 130-y-old stand. All stands established after fire. Leaf area index (LAI) ranged between 0.6 (28-y-old stand) and 1.6 for stands older than 67-y. Stand xylem area at 1.3 m height increased from 4 cm2 m−2 (28-y) to 11.5 cm2 m−2 (67-y) and decreased again to 7 cm2 m−2 in old stands. Above-ground living biomass increased from 1.5 kg dry weight m−2 (28-y) to 14 kg dry weight m−2 (383-y). Day-to-day variation of tree transpiration in summer was dependent on net radiation, vapour pressure deficit, and soil water stress. Tree-to-tree variation of xylem flux was small and increased with heterogeneity in canopy structure. Maximum rates of xylem flux density followed the course of net radiation from mid April when a constant level of maximum rates was reached until mid September when low temperatures and light strongly reduced flux density. Maximum sap flux density (60 g m−2 s−1) and canopy transpiration (1.5 mm d−1) were reached in the 67-y stand. Average canopy transpiration of all age classes was 0.72 ± 0.3 mm d−1. Canopy transpiration (E) was not correlated with LAI but related to stand sapwood area SA (E = − 0.02 + 1.15SA R2) which was determined by stand density and tree sapwood area.

Notes: The soil nitrogen cycle was investigated in a pre-established Lolium perenne sward on a loamy soil and exposed to ambient and elevated atmospheric CO2 concentrations (350 and 700 μL L−1) and, at elevated [CO2], to a 3 °C temperature increase. At two levels of mineral nitrogen supply, N– (150 kgN ha−1 y−1) and N+ (533 kgN ha−1 y−1), 15N-labelled ammonium nitrate was supplied in split applications over a 2.5-y period. The recovery of the labelled fertilizer N was measured in the harvests, in the stubble and roots, in the macro-organic matter fractions above 200 μm in size (MOM) and in the aggregated organic matter below 200 μM (AOM). Elevated [CO2] reduced the total amount of N harvested in the clipped parts of the sward. The harvested N derived from soil was reduced to a greater extent than that derived from fertilizer. At both N supplies, elevated [CO2] modified the allocation of the fertilizer N in the sward, in favour of the stubble and roots and significantly increased the recovery of fertilizer N in the soil macro-organic matter fractions. The increase of fertilizer N immobilization in the MOM was associated with a decline of fertilizer N uptake by the grass sward, which supported the hypothesis of a negative feedback of elevated [CO2] on the sward N yield and uptake. Similar and even more pronounced effects were observed for the native N mineralized in the soil. At N–, a greater part of the fertilizer N organized in the root phytomass resulted in an underestimation of N immobilized in dead roots and, in turn, an underestimation of N immobilization in the MOM. The 3 °C temperature increase alleviated the [CO2] effect throughout much of the N cycle, increasing soil N mineralization, N derived from soil in the harvests, and the partitioning of the assimilated fertilizer N to shoots. In conclusion, at ambient temperature, the N cycle was slowed down under elevated [CO2], which restricted the increase in the aboveground production of the grass sward, and apparently contributed to the sequestration of carbon belowground. In contrast, a temperature increase under elevated [CO2] stimulated the soil nitrogen cycle, improved the N nutrition of the sward and restricted the magnitude of the soil C sequestration.

Notes: Changes in soil organic carbon (SOC) in agricultural soils influence soil quality and greenhouse gas concentrations in the atmosphere. Land use, management practices, soil characteristics, and climate influence such changes. Using the Century model we estimated the rate of SOC change in agricultural soils of Canada for the period 1970 to 2010. This estimation was based on the estimated SOC change for 15% of the 1250 agriculturally designated soil landscape of Canada (SLC) polygons. Simulations were carried out for two to five crop rotations and for conventional and no-tillage. The results indicate that the agricultural soils in Canada, whose SOC are currently very close to equilibrium, will stop being a net source of CO2 and will become a sink by the year 2000. Rates of carbon change for the years 1970, 1990, and 2010 were estimated to be −67, − 39, and 11 kgC ha−1. The rate of decline in the carbon content of agricultural soils in Canada has slowed considerably in the 1990s as a result of an increase in the adoption of no-tillage management, a reduction in the use of summer fallowing, and an increase in fertilizer application. We estimate that the proportion of agricultural land storing SOC will have increased from 17% in 1990 to 53% by the year 2000.

Notes: Raised bogs are among the ecosystems most susceptible to atmospheric nitrogen pollution. Based on global data ranging from pristine to heavily polluted areas, a conceptual model is presented to explain the logistic response of these terrestrial carbon reservoirs to increased airborne nitrogen fluxes.

Notes: This paper reports the range and statistical distribution of oxidation rates of atmospheric CH4 in soils found in Northern Europe in an international study, and compares them with published data for various other ecosystems. It reassesses the size, and the uncertainty in, the global terrestrial CH4 sink, and examines the effect of land-use change and other factors on the oxidation rate.Only soils with a very high water table were sources of CH4; all others were sinks. Oxidation rates varied from 1 to nearly 200 μg CH4 m−2 h−1; annual rates for sites measured for ≥1 y were 0.1–9.1 kg CH4 ha−1 y−1, with a log-normal distribution (log-mean ≈ 1.6 kg CH4 ha−1 y−1). Conversion of natural soils to agriculture reduced oxidation rates by two-thirds –- closely similar to results reported for other regions. N inputs also decreased oxidation rates. Full recovery of rates after these disturbances takes 〉 100 y. Soil bulk density, water content and gas diffusivity had major impacts on oxidation rates. Trends were similar to those derived from other published work. Increasing acidity reduced oxidation, partially but not wholly explained by poor diffusion through litter layers which did not themselves contribute to the oxidation. The effect of temperature was small, attributed to substrate limitation and low atmospheric concentration.Analysis of all available data for CH4 oxidation rates in situ showed similar log-normal distributions to those obtained for our results, with generally little difference between different natural ecosystems, or between short-and longer-term studies. The overall global terrestrial sink was estimated at 29 Tg CH4 y−1, close to the current IPCC assessment, but with a much wider uncertainty range (7 to 〉 100 Tg CH4 y−1). Little or no information is available for many major ecosystems; these should receive high priority in future research.

Notes: Small open-top chambers (OTC) are used widely in ecosystem warming experiments. The efficacy of the open-top chamber as an analogue of climatic warming is examined. Twenty-four small OTCs were used to passively warm canopy temperatures in wet meadow tundra at Barrow, Alaska, during two consecutive summers with contrasting surface air-temperatures. Fortuitously, the seasonal average temperature regime within chambers in the colder year (1995) was similar to the controls of the warmer year (1996); this allowed a comparison of natural vs. chamber warming. All measured plant responses behaved similarly to both year and treatment 68% of the time. A comparison of the populations of the warmer summer's control with the cooler summer's OTC found no statistical difference in 80% of the response variables measured. A meta-analysis also found no significant difference between the responses of the two populations. These results give empirical biotic validation for the use of the OTC as an analogue of regional climate warming.

Notes: After a step increase in the atmospheric partial pressure of CO2 (pCO2), the availability of mineral N may be insufficient to meet the plant's increased demand for N. Over time, however, the ecosystem may adapt to the new conditions, and a new equilibrium may be established in the fluxes of C and N. This would result in a higher dry mass (DM) yield response of the plants to elevated pCO2.The effect of elevated atmospheric pCO2 (60 Pa pCO2) was studied in Lolium perenne L. swards with two N fertilization treatments (14 and 56 g m−2 y−1) in a six-year FACE (Free Air Carbon dioxide Enrichment) experiment. In the high N treatment, the input of N with fertilizer considerably exceeded the export of N with the harvested plant material in both CO2 treatments leading to an apparent net input of N into the ecosystem. Accordingly, the proportion of harvested N derived from 15N labelled fertilizer N, applied throughout the experiment (〈 6 years), increased over the years. Under these high N conditions, the annual DM yield response of the Lolium perenne sward to elevated pCO2 increased (from 7% in 1993 to 25% in 1998). In parallel, the response of N yield to elevated pCO2 increased, and the initially negative effect of elevated pCO2 on specific leaf area (SLA) disappeared. The high N input system seemed to overcome in part an initially limiting effect of N on the yield response to elevated pCO2 within a few years. In contrast, there was no apparent net input of N into the ecosystem in the low N treatment, because N fertilization just compensated the export of N with the harvested plant material. Accordingly, the proportion of harvested N yield, derived from fertilizer N, which was applied throughout the experiment, remained low. At low N, the availability of mineral N strongly limited plant growth and yield production in both CO2 treatments; the low yields of DM and N, the low concentration of N in the plant material, and the low SLA reflected this. Although the plants grew under the same environmental conditions and the same management treatment as plants in the high N treatment, the response of DM yields to elevated pCO2 in the low N treatment remained weak throughout the experiment (5% in 1993 and 9% in 1998). The results are discussed in the context of the sizes of the different N pools in the soil, the allocation of N within the plant and the possible effects on temporal immobilization, and the availability of mineral N for yield production as affected by elevated pCO2 and N fertilization.

Notes: We conducted ecosystem carbon and water vapour exchange studies in an old-growth Pinus ponderosa forest in the Pacific North-west region of the United States. The canopy is heterogeneous, with tall multiaged trees and an open, clumped canopy with low leaf area. Carbon assimilation can occur throughout relatively mild winters, although night frosts can temporarily halt the process and physiological factors limit its efficiency. In contrast, carbon assimilation is often limited in the ‘growing season’ by stomatal closure associated with high evaporative demand (D) and soil water deficits. All of these factors present a challenge to effectively modelling ecosystem processes. Our objective was to generate an understanding of the controls on ecosystem processes across seasonal and annual cycles from a combination of fine-scale process modelling, ecophysiological measurements, and carbon and water vapour fluxes measured by the eddy covariance method. Flux measurements showed that 50% and 70% of the annual carbon uptake occurred outside the ‘growing season’ (defined as bud break to senescence, ∼ days 125–275) in 1996 and 1997. On a daily basis in summer, net ecosystem productivity (NEP) was low when D and soil water deficits were large. Whole ecosystem water vapour fluxes (LE) increased from spring to summer (1.0–1.9 mm d−1) as conducting leaf area increased by 30% and as evaporative demand increased, while evaporation from the soil surface became a smaller portion of total LE as soil water deficits increased. The models underestimated soil evaporation, particularly following rain. In the SPA model, varying the temperature optimum for photosynthesis seasonally resulted in overestimation of carbon uptake in winter and spring, showing that in coniferous forests, assumptions about temperature optima are clearly important. Daily estimates of soil surface CO2 flux from measurements and site meteorological data demonstrated that modelling of soil CO2 flux based on an Arrhenius-type equation in CANPOND overestimated CO2 respired from the soil during drought and when temperatures were low.

Notes: How might wild relatives of modern cereals have responded to past, and how might they respond to future, atmospheric CO2 enrichment under competitive situations in a dry, low-nutrient environment? In order to test this, Aegilops and Hordeum species, common in semiarid annual grasslands of the Middle East, were grown in nine model ecosystems (400 kg each) with a natural matrix of highly diverse Negev vegetation established on native soil shipped to Basel, Switzerland. In a simulated, seasonally variable climate of the northern Negev, communities experienced a full life-cycle in 280 (preindustrial), 440 (immediate future) and 600 ppm of CO2 (end of the next century). Neither Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum showed a significant biomass response to CO2 concentrations exceeding 280 ppm The reproductive output remained unaffected or even declined (A. peregrina) under elevated CO2. Non-structural carbohydrates in leaf tissues increased and N concentration decreased with increasing CO2 concentration. N concentration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO2 treatment of parent plants. In a separate fertilizer × CO2 trial with A. kotschyi nested in smaller model communities, we found no effect of P addition, but a 2–3-fold biomass increase by NPK addition compared to the unfertilized control. A significant stimulation of biomass by CO2 enrichment (+ 44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that increased CO2 concentration had little direct effect on growth and reproduction in these ‘wild cereals’ in the recent past, and the same seems to hold for their future, except if N-rich fertilizer is added.

Notes: Regional analysis of greenhouse gas emissions is becoming increasingly important in answering questions related to environmental change, and typically employs a Geographic Information System (GIS) linked with a process-based simulation model. For the Northern Atlantic Zone (NAZ) in Costa Rica (281 649 ha), a regional analysis of soil–atmosphere nitrous oxide fluxes from the dominant land-use types forest, cattle pastures, and banana plantations was performed with both deterministic and stochastic variable representations. The stochastic representation accounted for soil and land management variability across nongeoreferenced fields within 1572 georeferenced land units in 13 relevant classes. Per class, frequency distributions of field-scale fluxes were simulated with a process-based model and Monte Carlo methods. Stochastic incorporation of both soil and land use variability resulted in areal (i.e. land unit-scale) fluxes that were 14–22% lower than estimates based on averaged inputs. Soil heterogeneity was dominant.In addition, spatial flux patterns for current (1992) land use and two alternative land-use scenarios were evaluated using stochastic inputs. With current management, the regional nitrous oxide-N flux (standard deviation in parentheses) from agricultural land was 0.43 (0.13) Gg y−1. Replacing natural grasses with mixtures of grasses and N-fixing species on relevant soil types and introducing different forms of banana plantation management (alternative I) increased the regional flux by 51% to 0.65 (0.22) Gg y−1. When all natural grasses were replaced by fertilized improved species and allowing different forms of banana plantation management (alternative II), the regional flux increased by 126% to 0.97 (0.68) Gg y−1.Using the revised IPCC methodology, the 1992 nitrous oxide emission from agriculture in the NAZ was estimated to be 0.32 Gg y−1. Due to formidable data requirements, regional analysis may not easily be used to produce country-level estimates. However, regional analysis does provide a valuable benchmark against which the more straightforward IPCC methodology can be evaluated.

Notes: Experiments were carried out to determine the effects of elevated atmospheric carbon dioxide (CO2) on phenolic biosynthesis in four plant species growing over three generations for nine months in a model plant community. Results were compared to those obtained when the same species were grown individually in pots in the same soils and controlled environment. In the model herbaceous plant community, only two of the four species showed any increase in biomass under elevated CO2, but this occurred only in the first generation for Spergula arvensis and in the second generation for Poa annua. Thus, the effects of CO2 on plant biomass and carbon and nitrogen content were species- and generation-specific. The activity of the principle phenolic biosynthetic enzyme, phenylalanine ammonia lyase (PAL), increased under elevated CO2 in Senecio vulgaris only in Generation 1, but increased in three of the four plant species in Generation 2. There were no changes in the total phenolic content of the plants, except for P. annua in Generation 1. Lignin content decreased under elevated CO2 in Cardamine hirsuta in Generation 1, but increased in Generation 2, whilst the lignin content of P. annua showed no change, decreased, then increased in response to elevated CO2 over the three generations. When the species were grown alone in pots, elevated CO2 increased PAL activity in plants grown in soil taken from the Ecotron community after nine months of plant growth, but not in plants grown in the soil used at the start of the experiment (‘initial' soil). In P. annua, phenolic biosynthesis decreased under elevated CO2 in initial soil, and in both P. annua and S. vulgaris there was a significant interaction between effects of soil type and CO2 level on PAL activity. In this study, plant chemical composition altered more in response to environmental factors such as soil type than in response to carbon supply. Results were species-specific and changed markedly between generations.

Notes: The effect of elevated atmospheric CO2 concentration (Ca) on soil carbon and nitrogen accumulation and soil microbial biomass and activity in a native Florida scrub oak community was studied. The plant community, dominated by Quercus myrtifolia Willd. and Q. geminata Small, was exposed for 2 years to elevated Ca in open-top chambers. Buried subsoil bags were retrieved after 1 year of exposure to elevated Ca. In addition, soil cores were taken twice from the chambers within two weeks in July 1998 (the first after a long dry spell and the second after 25 mm of rainfall) and divided into rhizosphere and bulk soil. Soil organic matter accumulation (excluding roots) into the buried subsoil bags was lower in elevated than in ambient Ca. Concentrations of soluble carbon and ninhydrin-reactive nitrogen (Nninh) in the rhizosphere soil were reduced by elevated Ca for the first sampling date and unaffected for the second sampling date. Microbial activity, measured as fluorescein diacetate (FDA) hydrolysis, decreased in elevated Ca for the first sampling date. Microbial biomass carbon and nitrogen in the bulk soil were unaffected by elevated Ca. There was no effect of elevated Ca on bacterial numbers in the rhizosphere.

Notes: Data from a national butterfly monitoring scheme were analysed to test for relationships between temperature and three phenological measures, duration of flight period and timing of both first and peak appearance. First appearances of most British butterflies has advanced in the last two decades and is strongly related to earlier peak appearance and, for multibrooded species, longer flight period. Mean dates of first and peak appearance are examined in relation to Manley's central England temperatures, using regression techniques. We predict that, in the absence of confounding factors, such as interactions with other organisms and land-use change, climate warming of the order of 1 °C could advance first and peak appearance of most butterflies by 2–10 days.

Notes: During the past century, annual mean temperature has increased by 0.75°C and precipitation has shown marked variation throughout the Mediterranean basin. These historical climate changes may have had significant, but presently undefined, impacts on the productivity and structure of sclerophyllous shrubland, an important vegetation type in the region. We used a vegetation model for this functional type to examine climate change impacts, and their interaction with the concurrent historical rise in atmospheric CO2. Using only climate and soil texture as data inputs, model predictions showed good agreement with observations of seasonal and regional variation in leaf and canopy physiology, net primary productivity (NPP), leaf area index (LAI) and soil water. Model simulations for shrubland sites indicated that potential NPP has risen by 25% and LAI by 7% during the past century, although the absolute increase in LAI was small. Sensitivity analysis suggested that the increase in atmospheric CO2 since 1900 was the primary cause of these changes, and that simulated climate change alone had negative impacts on both NPP and LAI. Effects of rising CO2 were mediated by significant increases in the efficiency of water-use in NPP throughout the region, as a consequence of the direct effect of CO2 on leaf gas exchange. This increase in efficiency compensated for limitation of NPP by drought, except in areas where drought was most severe. However, while water was used more efficiently, total canopy water loss rose slightly or remained unaffected in model simulations, because increases in LAI with CO2 counteracted the effects of reduced stomatal conductance on transpiration. Model simulations for the Mediterranean region indicate that the recent rise in atmospheric CO2 may already have had significant impacts on productivity, structure and water relations of sclerophyllous shrub vegetation, which tended to offset the detrimental effects of climate change in the region.

Notes: Soil microbial biomass C (Cmic) is a sensitive indicator of trends in organic matter dynamics in terrestrial ecosystems. This study was conducted to determine the effects of tropospheric CO2 or O3 enrichments and moisture variations on total soil organic C (Corg), mineralizable C fraction (CMin), Cmic, maintenance respiratory (qCO2) or Cmic death (qD) quotients, and their relationship with basal respiration (BR) rates and field respiration (FR) fluxes in wheat-soybean agroecosystems. Wheat (Triticum aestivum L.) and soybean (Glycine max. L. Merr) plants were grown to maturity in 3-m dia open-top field chambers and exposed to charcoal-filtered (CF) air at 350 μL CO2 L−1; CF air + 150 μL CO2 L−1; nonfiltered (NF) air + 35 nL O3 L−1; and NF air + 35 nL O3 L−1 + 150 μL CO2 L−1 at optimum (− 0.05 MPa) and restricted soil moisture (− 1.0 ± 0.05 MPa) regimes. The + 150 μL CO2 L−1 additions were 18 h d−1 and the + 35 nL O3 L−1 treatments were 7 h d−1 from April until late October. While Corg did not vary consistently, CMin, Cmic and Cmic fractions increased in soils under tropospheric CO2 enrichment (500 μL CO2 L−1) and decreased under high O3 exposures (55 ± 6 nL O3 L−1 for wheat; 60 ± 5 nL O3 L−1 for soybean) compared to the CF treatments (25 ± 5 nL O3 L−1). The qCO2 or qD quotients of Cmic were also significantly decreased in soils under high CO2 but increased under high O3 exposures compared to the CF control. The BR rates did not vary consistently but they were higher in well-watered soils. The FR fluxes were lower under high O3 exposures compared to soils under the CF control. An increase in Cmic or Cmic fractions and decrease in qCO2 or qD observed under high CO2 treatment suggest that these soils were acting as C sinks whereas, reductions in Cmic or Cmic fractions and increase in qCO2 or qD in soils under elevated tropospheric O3 exposures suggest the soils were serving as a source of CO2.

Notes: Laboratory experiments were conducted with three California agricultural soils to examine substrate and process controls over temporal variability of NO and N2O production during nitrification, and to quantify the kinetics of HNO2-mediated chemical reactions. Gross NO production rates were highly correlated (r2 = 0.93–0.97) with calculated concentrations of HNO2, which were shown to originate from autotrophic microbial oxidation of NH4 + to NO2 − Production of NO was not correlated with NH4 + or NO3–, or with the overall nitrification rate. Distinct periods of high NO2– accumulation occurred below critical pH values in each soil, apparently due to inhibition of microbial NO2– oxidation. Data suggest that even during periods of relatively low NO2– accumulation and rapid overall nitrification, HNO2-mediated reactions may have been the primary source of NO. Rate coefficients (kPNO) relating NO production to HNO2 concentrations were determined for sterile (λ-irradiated) soils, and were similar to kPNO values in 2 of 3 nonsterile soils undergoing nitrification. Production of N2O was correlated with HNO2 (r2 = 0.88–0.99) in sterile soils, and with NO2– and NO3– (R2 = 0.72–0.91) in nonsterile soils. Experiments using 15N confirmed that dissimilatory NO3– reduction contributed to N2O production even under primarily aerobic conditions. Sterile kPNO and kPN2O values were correlated (r2 = 0.90 and 0.82) with soil organic matter content. Overall, the results demonstrate that both steps of the nitrification sequence, together with abiotic reactions involving NO2–/HNO2 need to be considered in developing improved models of NO and N2O emissions from soils.

Notes: Current ecosystem model predictions concerning the effects of global temperature increase on forest responses do not account for factors influencing long-term evolutionary dynamics of natural populations. Population structure and genetic variability may represent important factors in a species' ability to adapt to global-scale environmental change without experiencing major alterations in current range limits. Genetic variation and structure in sugar maple (Acer saccharum Marsh.) were examined across three regions, between two stands within regions, and among four to five open-pollinated families within stands (total N = 547 genotypes) using 58 randomly amplified polymorphic DNA (RAPD) markers. Differences within open-pollinated families account for the largest portion of the total variation (29%), while differences among regions represent less than 2% of the total variation. Genetic diversity, as indicated by estimates of percent polymorphic loci, expected heterozygosity, fixation coefficients, and genetic distance, is greatest in the southern region, which consists of populations with the maximum potential risk due to climate change effects. The high level of genetic similarity (greater than 90%) among some genotypes suggests that gene flow is occurring among regions, stands, and families. High levels of genetic variation among families indicate that vegetational models designed to predict species' response to global-scale environmental change may need to consider the degree and hierarchical structure of genetic variation when making large-scale inferences.

Notes: We examined interactions between temperature, soil development, and decomposition on three elevational gradients, the upper and lower ends of each being situated on a common lava flow or ash deposit. We used the reciprocal transplant technique to estimate decomposition rates of Metrosideros polymorpha leaf litter during a three-year period at warm and cool ends of each gradient. Litter quality was poorest early in soil development or where soils were most intensely leached and waterlogged. In situ litter decomposition was slowest on the young 1855 flow (k=  0.26 and 0.14 at low and high elevation, respectively). The more fertile Laupahoehoe gradient also supported more rapid in situ decay at the warmer low elevation site (k=  0.90) than at high elevation (k=  0.51). The gradient with the most advanced soil development showed no difference for in situ decay at low and high elevations (k=  0.88 and 0.99, respectively) probably due to low soil nutrient availability at low elevation, which counteracted the effect of warmer temperature. Comparisons of in situ, common litter, and common site experiments indicated that site factors influenced decomposition more than litter quality did. The effect of temperature, however, could be over-ridden by soil fertility or other site factors. Field gradient studies of this sort yield variable estimates of apparent Q10, even under the best conditions, due to interactions among temperature, moisture, nutrient availability, decomposer communities and litter quality. Such interactions may be as likely to occur with changing climate as they are along elevational gradients.

Notes: The long-term effects of elevated (ambient plus 350 μmol mol−1) atmospheric CO2 concentration (Ca) on the leaf senescence of Quercus myrtifolia Willd was studied in a scrub-oak community during the transition from autumn (December 1997) to spring (April 1998). Plants were grown in large open-top chambers at the Smithsonian CO2 Research Site, Merritt Island Wildlife Refuge, Cape Canaveral, Florida. Chlorophyll (a + b) concentration, Rubisco activity and N concentration decreased by 75%, 82%, and 52%, respectively, from December (1997) to April (1998) in the leaves grown at ambient Ca. In contrast, the leaves of plants grown at elevated Ca showed no significant decrease in chlorophyll (a + b) concentration or Rubisco activity, and only a 25% reduction in nitrogen. These results indicate that leaf senescence was delayed during this period at elevated Ca. Delayed leaf senescence in elevated Ca had important consequences for leaf photosynthesis. In elevated Ca the net photosynthetic rate of leaves that flushed in Spring 1997 (last year's leaves) and were 13 months old was not different from fully-expanded leaves that flushed in 1998, and were approximately 1 month old (current year's leaves). In ambient Ca the net photosynthetic rate of last year's leaves was 54% lower than for current year's leaves. When leaves were fully senesced, nitrogen concentration decreased to about 40% of the concentration in non-senesced leaves, in both CO2 treatments. In April, net photosynthesis was 97% greater in leaves grown in elevated Ca than in those grown at ambient. During the period when elevated Ca delayed leaf senescence, more leaves operating at higher photosynthetic rate would allow the ecosystem dominated by Q. myrtifolia to gain more carbon at elevated Ca than at ambient Ca.

Notes: This article presents the logical reasoning underlying the optimal design of an experiment. We used Free-Air Carbon dioxide Enrichment (FACE) experiments to illustrate this trade-off as such experiments are particularly costly. On a theoretical basis, two-way nested designs and split-plot designs have similar power in testing carbon dioxide (CO2) main effects. If researchers have the choice of adding two replicate rings or two control plots to their experiment, our results show that both options provide a substantial gain in statistical power, with a slightly greater gain in the former case and at reduced financial cost in the latter. The former option, however, provides an insurance against possible ring failure.On an empirical basis, we analysed a preliminary FACE photosynthesis dataset collected at Duke University. The experiment was designed as a split-plot design to test the effects of growth environment (GROWTH) and measurement CO2 concentration (MEAS) on photosynthetic rates of loblolly pine. Although a significant effect of MEAS was observed, we failed to detect a significant main effect of GROWTH. Power analysis was used to understand why the GROWTH main effect was not significant. The minimum detectable difference between treatment means that we calculated for GROWTH in this experiment was 4.04 μmol CO2 m−2 s−1 for a statistical power of 0.90, whereas the observed difference was 0.16 μmol CO2 m−2 s−1.Our recommendations for the design of FACE experiments are: (i) consider a second treatment factor with many levels within each ring in order to obtain a split-plot design that provides a powerful test of interaction between treatment factors; (ii) add control plots, unless financial constrictions disallow for necessary personnel; (3) pool the data of FACE experiments conducted in comparable ecosystems (e.g. forests or grasslands), with two rings per treatment level at each site.

Notes: Among plants grown under enriched atmospheric CO2, root:shoot balance (RSB) theory predicts a proportionately greater allocation of assimilate to roots than among ambient-grown plants. Conversely, defoliation, which decreases the plant's capacity to assimilate carbon, is predicted to increase allocation to shoot. We tested these RSB predictions, and whether responses to CO2 enrichment were modified by defoliation, using Heterotheca subaxillaris, an annual plant native to south-eastern USA. Plants were grown under near-ambient (400 μmol mol−1) and enriched (700 μmol mol−1) levels of atmospheric CO2. Defoliation consisted of the weekly removal of 25% of each new fully expanded, but not previously defoliated, leaf from either rosette or bolted plants. In addition to dry mass measurements of leaves, stems, and roots, Kjeldahl N, protein, starch and soluble sugars were analysed in these plant components to test the hypothesis that changes in C:N uptake ratio drive shifts in root:shoot ratio. Young, rapidly growing CO2-enriched plants conformed to the predictions of RSB, with higher root:shoot ratio than ambient-grown plants (P 〈 0.02), whereas older, slower growing plants did not show a CO2 effect on root:shoot ratio. Defoliation resulted in smaller plants, among which both root and shoot biomass were reduced, irrespective of CO2 treatment (P 〈 0.03). However, H. subaxillaris plants were able to compensate for leaf area removal through flexible shoot allocation to more leaves vs. stem (P 〈 0.01). Increased carbon availability through CO2 enrichment did not enhance the response to defoliation, apparently because of complete growth compensation for defoliation, even under ambient conditions. CO2-enriched plants had higher rates of photosynthesis (P 〈 0.0001), but this did not translate into increased final biomass accumulation. On the other hand, earlier and more abundant yield of flower biomass was an important consequence of growth under CO2 enrichment.

Notes: Leaf phenology describes the seasonal cycle of leaf functioning. Although it is essential for understanding the interactions between the biosphere, the climate, and biogeochemical cycles, it has received little attention in the modelling community at global scale. This article focuses on the prediction of spatial patterns of the climatological onset date of leaf growth for the decade 1983–93. It examines the possibility of extrapolating existing local models of leaf onset date to the global scale. Climate is the main variable that controls leaf phenology for a given biome at this scale, and satellite observations provide a unique means to study the seasonal cycle of canopies. We combine leaf onset dates retrieved from NOAA/AVHRR satellite NDVI with climate data and the DISCover land-cover map to identify appropriate models, and determine their new parameters at a 0.5° spatial resolution. We define two main regions: at temperate and high latitudes leaf onset models are mainly dependent on temperature; at low latitudes they are controlled by water availability. Some local leaf onset models are no longer relevant at the global scale making their calibration impossible. Nevertheless, we define our unified model by retaining the model that best reproduced the spatial distribution of leaf onset dates for each biome. The main spatial patterns of leaf onset date are well simulated, such as the Sahelian gradient due to aridity and the high latitude gradient due to frost. At temperate and high latitudes, simulated onset dates are in good agreement with climatological observations; 62% of treated grid-cells have a simulated leaf onset date within 10 days of the satellite observed onset date (which is also the temporal resolution of the NDVI data). In tropical areas, the subgrid heterogeneity of the phenology is larger and our model's predictive power is diminished. The difficulties encountered in the tropics are due to the ambiguity of the satellite signal interpretation and the low reliability of rainfall and soil moisture fields.

Notes: The ability of plant species to migrate is one of the critical issues in assessing accurately the future response of the terrestrial biosphere to climate change. This ability is confined by both natural and human-induced changes in land cover. In this paper we present land-cover and Carbon (C) cycle models designed to simulate the biospheric consequences of different types of land-cover changes. These models, imbedded in the larger integrated assessment model IMAGE 2, were used to demonstrate the importance of considering spatial aspects for global C-cycle modelling. A gradual-migration, an unlimited-migration and a no-migration case were compared to show the range of possible consequences. Major differences between these cases were simulated for land-cover patterns and the carbon budget. A large geographical variation in the biospheric response was also simulated. The strongest response was simulated in high-latitude regions, especially for the migration cases in which land-cover changes were permitted. In low-latitudes regions the differences between the migration cases were smaller, mainly due to the effects of land-use changes. The geographical variation among, and the different responses, the migration cases clearly demonstrate how essential it is to assess biospheric responses to climate change and land use simultaneously. Moreover, it also shows the urgent need for enhanced understanding of spatial and temporal dynamics of the biospheric responses.

Notes: Three grassland communities in New Zealand with differing climates and proportions of C3 and C4 species were subjected to one-off extreme heating (eight hours at 52.5°C) and rainfall (the equivalent of 100 mm) events. A novel experimental technique using portable computer-controlled chambers simulated the extreme heating events. The productive, moist C3/C4 community was the most sensitive to the extreme events in terms of short-term community composition compared with a dry C3/C4 community or an exclusively C3 community. An extreme heating event caused the greatest change to plant community species abundance by favouring the expansion of C4 species relative to C3 species, shifting C4 species abundance from 43% up to 84% at the productive, moist site. This was observed both in the presence and absence of added water. In the absence of C4 species, heating reduced community productivity by over 60%. The short-term shifts in the abundance of C3 and C4 species in response to the single extreme climatic events did not have persistent effects on community structure or on soil nitrogen one year later. There was no consistent relationship between diversity and stability of biomass production of these plant communities, and species functional identity was the most effective explanation for the observed shifts in biomass production. The presence of C4 species resulted in an increased stability of productivity after extreme climatic events, but resulted in greater overall shifts in community composition. The presence of C4 species may buffer grassland community productivity against an increased frequency of extreme heating events associated with future global climate change.

Notes: Although legumes showed a clearly superior yield response to elevated atmospheric pCO2 compared to nonlegumes in a variety of field experiments, the extent to which this is due to symbiotic N2 fixation per se has yet to be determined. Thus, effectively and ineffectively nodulating lucerne (Medicago sativa L.) plants with a very similar genetic background were grown in competition with each other on fertile soil in the Swiss FACE experiment in order to monitor their CO2 response. Under elevated atmospheric pCO2, effectively nodulating lucerne, thus capable of symbiotically fixing N2, strongly increased the harvestable biomass and the N yield, independent of N fertilization. In contrast, the harvestable biomass and N yield of ineffectively nodulating plants were affected negatively by elevated atmospheric pCO2 when N fertilization was low. Large amounts of N fertilizer enabled the plants to respond more favourably to elevated atmospheric pCO2, although not as strongly as effectively nodulating plants. The CO2-induced increase in N yield of the effectively nodulating plants was attributed solely to an increase in symbiotic N2 fixation of 50–175%, depending on the N fertilization treatment. N yield derived from the uptake of mineral N from the soil was, however, not affected by elevated pCO2. This result demonstrates that, in fertile soil and under temperate climatic conditions, symbiotic N2 fixation per se is responsible for the considerably greater amount of above-ground biomass and the higher N yield under elevated atmospheric pCO2. This supports the assumption that symbiotic N2 fixation plays a key role in maintaining the C/N balance in terrestrial ecosystems in a CO2-rich world.

Notes: An increase in concentration of atmospheric CO2 is one major factor influencing global climate change. Among the consequences of such an increase is the stimulation of plant growth and productivity. Below-ground microbial processes are also likely to be affected indirectly by rising atmospheric CO2 levels, through increased root growth and rhizodeposition rates. Because changes in microbial community composition might have an impact on symbiotic interactions with plants, the response of root nodule symbionts to elevated atmospheric CO2 was investigated. In this study we determined the genetic structure of 120 Rhizobium leguminosarum bv. trifolii isolates from white clover plants exposed to ambient (350 μmol mol−1) or elevated (600 μmol mol−1) atmospheric CO2 concentrations in the Swiss FACE (Free-Air-Carbon-Dioxide-Enrichment) facility. Polymerase Chain Reaction (PCR) fingerprinting of genomic DNA showed that the isolates from plants grown under elevated CO2 were genetically different from those isolates obtained from plants grown under ambient conditions. Moreover, there was a 17% increase in nodule occupancy under conditions of elevated atmospheric CO2 when strains of R. leguminosarum bv. trifolii isolated from plots exposed to CO2 enrichment were evaluated for their ability to compete for nodulation with those strains isolated from ambient conditions. These results indicate that a shift in the community composition of R. leguminosarum bv. trifolii occurred as a result of an increased atmospheric CO2 concentration, and that elevated atmospheric CO2 affects the competitive ability of root nodule symbionts, most likely leading to a selection of these particular strains to nodulate white clover.

Notes: Understanding the response of terrestrial ecosystems to climatic warming is a challenge because of the complex interactions of climate, disturbance, and recruitment across the landscape. We use a spatially explicit model (ALFRESCO) to simulate the transient response of subarctic vegetation to climatic warming on the Seward Peninsula (80 000 km2) in north-west Alaska. Model calibration efforts showed that fire ignition was less sensitive than fire spread to regional climate (temperature and precipitation). In the model simulations a warming climate led to slightly more fires and much larger fires and expansion of forest into previously treeless tundra. Vegetation and fire regime continued to change for centuries after cessation of the simulated climate warming. Flammability increased rapidly in direct response to climate warming and more gradually in response to climate-induced vegetation change. In the simulations warming caused as much as a 228% increase in the total area burned per decade, leading to an increasingly early successional and more homogenous deciduous forest-dominated landscape. A single transient 40-y drought led to the development of a novel grassland–steppe ecosystem that persisted indefinitely and caused permanent increases in fires in both the grassland and adjacent vegetation. These simulated changes in vegetation and disturbance dynamics under a warming climate have important implications for regional carbon budgets and biotic feedbacks to regional climate.

Notes: We measured a cut-away peatland's CH4 dynamics using the static chamber technique one year before and two years after restoration (rewetting). The CH4 emissions were related to variation in vegetation and abiotic factors using multiple linear regression. A statistical model for CH4 flux with cottongrass cover (Eriophorum vaginatum L.), soil temperature, water level, and effective temperature sum index as driving variables explained most (r2 = 0.81) of the temporal and spatial variability in the fluxes. In addition to the direct increasing effect of raised water level on CH4 emissions, rewetting also promoted an increase of cottongrass cover which consequently increased carbon flux (substrate availability) into the system. The seasonal CH4 dynamics in tussocks followed seasonal CO2 dynamics till mid August but in late autumn CH4 emissions increased while CO2 influxes decreased. The reconstructed seasonal CH4 exchange was clearly higher following the rewetting, although it was still lower than emissions from pristine mires in the same area. However, our simulation for closed cottongrass vegetation showed that CH4 emissions from restored peatlands may remain at a lower level for a longer period of time even after sites have become fully vegetated and colonized by mire plants.

Notes: The effect of elevated carbon dioxide levels on total bacterial communities was studied in a series of controlled and replicated model terrestrial ecosystems over a period of 38 weeks. The bacterial community was profiled using Denaturing Gradient Gel Electrophoresis (DGGE) analysis of bacterial 16S rRNA gene fragments amplified by the Polymerase Chain Reaction from DNA extracted directly from soil. Bacterial community DGGE profiles provided three major findings: (i) there was a high degree of profile similarity after ≈ 12 weeks (one plant generation); (ii) whilst overall DGGE profile was maintained over the 38 weeks (three plant generations), the banding patterns became more diverse with time; (iii) DGGE data provided no evidence for a shift in bacterial community structure resulting from exposure of the ecosystem to an increased atmospheric CO2 level.

Notes: Landscape- and community-level CO2 measurements were made at a subarctic sedge fen near Churchill Manitoba during the 1997 growing season. Climatic conditions were warmer and drier than the 30-y normal. Landscape-scale micrometeorological measurements indicated that the wetland gained 49 g CO2 m−2 during the growing season. Chamber-scale measurements from the main vegetation community types showed that small hummocks (Carex spp. sites) dominated the CO2 exchange, yielding an effective scaling factor of 70%. Scaled parameters of two algorithms describing photosynthesis and respiration for each community type show strong similarity to those derived at the landscape level. Scaling photosynthesis, respiration, and net ecosystem CO2 exchange from the community to landscape-level over the season is within the maximum probable error of each methodological approach and helps substantiate the 1997 CO2 budget. We explore the equilibrium response of net ecosystem CO2 exchange of this fen to climatic change by examining the feedback of water table position on vegetation distribution and nitrogen availability. Based on the effective scaling factors computed for each community type, we hypothesize that a small decrease in mean water table position could nearly triple the net uptake of CO2 at this wetland.

Notes: The purpose of this study was to test for direct inhibition of rice canopy apparent respiration by elevated atmospheric carbon dioxide concentration ([CO2]) across a range of short-term air temperature treatments. Rice (cv. IR-72) was grown in eight naturally sunlit, semiclosed, plant growth chambers at daytime [CO2] treatments of 350 and 700 μmol mol−1. Short-term night-time air temperature treatments ranged from 21 to 40 °C. Whole canopy respiration, expressed on a ground area basis (Rd), was measured at night by periodically venting the chambers with ambient air. This night-time chamber venting and resealing procedure produced a range of increasing chamber [CO2] which we used to test for potential inhibitory effects of rising [CO2] on Rd. A nitrous oxide leak detection system was used to correct Rd measurements for chamber leakage rate (L) and also to determine if apparent reductions in night-time Rd with rising [CO2] could be completely accounted for by L. The L was affected by both CO2 concentration gradient between the chamber and ambient air and the inherent leakiness of each individual chamber. Nevertheless, after correcting Rd for L, we detected a rapid and reversible, direct inhibition of Rd with rising chamber [CO2] for air temperatures above 21 °C. This effect was larger for the 350 compared with the 700 μmol mol−1 daytime [CO2] treatment and was also increased with increasing short-term air temperature treatments. However, little difference in Rd was found between the two daytime [CO2] treatments when night-time [CO2] was at the respective daytime [CO2]. These results suggest that naturally occurring diurnal changes in both ambient [CO2] and air temperature can affect Rd. Because naturally occurring diurnal changes in both [CO2] and air temperature can be expected in a future higher CO2 world, short-term direct effects of these environmental variables on rice Rd can also be expected.

Notes: Previous studies have demonstrated that coral and algal calcification is tightly regulated by the calcium carbonate saturation state of seawater. This parameter is likely to decrease in response to the increase of dissolved CO2 resulting from the global increase of the partial pressure of atmospheric CO2. We have investigated the response of a coral reef community dominated by scleractinian corals, but also including other calcifying organisms such as calcareous algae, crustaceans, gastropods and echinoderms, and kept in an open-top mesocosm. Seawater pCO2 was modified by manipulating the pCO2 of air used to bubble the mesocosm. The aragonite saturation state (Ωarag) of the seawater in the mesocosm varied between 1.3 and 5.4. Community calcification decreased as a function of increasing pCO2 and decreasing Ωarag. This result is in agreement with previous data collected on scleractinian corals, coralline algae and in a reef mesocosm, even though some of these studies did not manipulate CO2 directly. Our data suggest that the rate of calcification during the last glacial maximum might have been 114% of the preindustrial rate. Moreover, using the average emission scenario (IS92a) of the Intergovernmental Panel on Climate Change, we predict that the calcification rate of scleractinian-dominated communities may decrease by 21% between the pre-industrial period (year 1880) and the time at which pCO2 will double (year 2065).

Notes: Measurements of the spatial variability of methane (CH4) emissions, net CO2 ecosystem exchange (NEE), and dissolved carbon (CH4, CO2, and DOC) were made in a boreal patterned peatland in northern Sweden in the summers (May to September) of 1992 and 1993. Carbon balance terms were measured and the carbon balance inferred at different peatland surface topography features (e.g. ridges, lawns, and pools) and at different positions within the peatland (e.g. plateau, margin). Combining these data permits a comparison of the carbon balance at the peatland scale for the two field seasons.Trends in the spatial variability of the net carbon storage, as determined by the difference between inputs and outputs, suggest that carbon storage decreased in lawns from the margin of the peatland to the central plateau, while the reverse trend occurred in ridges. This indicates a difference in carbon exchange processes between sites with different surface topography due to differences in soil moisture and temperature.Total carbon storage for the peatland, weighted for topographic variability, indicates that the peatland gained carbon in 1992 (2.0 g C m− 2), but lost carbon in 1993 ( −  7.6 g C m− 2). There was little variation in mean seasonal air temperature and total precipitation between the two years suggesting that the timing and magnitude of temperature and precipitation variation within the growing season are important for the season carbon balance. Because the carbon storage differences were small relative to the potential errors we conclude that the peatland was neither a net sink nor source of atmospheric carbon. This research demonstrates the importance of position in a peatland for the inference of long-term carbon accumulation and the assessment of contemporary exchange rates.

Notes: Empirical equations are parameterized for use with chlorophyll a, derived from satellite ocean colour data, to calculate phytoplankton carbon production, phytoplankton new production, and export production. For environments in a high variance (HV) pigment statistical class, annual phytoplankton particulate organic carbon production (AIP) is linearly related to annual average in situ chlorophyll a within the near-surface layer. Linear relations were also obtained between AIP and annual new nitrogen production, and between AIP and particulate organic carbon annually exported from the euphotic zone for environments in that class. We found no relation between AIP and CSFC, or between the annual production variables, for oceanic environments characterized by low pigment variance (LV). Ratios of export production to AIP, called e, and new production to nitrogen annually used in phytoplankton production, called f, are widely used to express marine food web processes. The trends of these ratios with AIP differ between HV and LV environments. This is a result of differences in the coupling between nitrogen and carbon transfer in pelagic food webs, which contain different organism size classes in HV compared to LV environments. We applied the empirical equations to CZCS data to estimate global new and export production. The HV environments are responsible for about 40% of global ocean annual phytoplankton carbon production and 70% of global ocean annual new and export production.

Notes: The impact of elevated CO2 and N-fertilization on soil C-cycling in Lolium perenne and Trifolium repens pastures were investigated under Free Air Carbon dioxide Enrichment (FACE) conditions. For six years, swards were exposed to ambient or elevated CO2 (35 and 60 Pa pCO2) and received a low and high rate of N fertilizer. The CO2 added in the FACE plots was depleted in 13C compared to ambient (Δ−  40‰) thus the C inputs could be quantified.On average, 57% of the C associated with the sand fraction of the soil was ‘new’ C. Smaller proportions of the C associated with the silt (18%) and clay fractions (14%) were derived from FACE. Only a small fraction of the total C pool below 10 cm depth was sequestered during the FACE experiment.The annual net input of C in the FACE soil (0–10 cm) was estimated at 4.6 ± 2.2 and 6.3 ± 3.6 (95% confidence interval) Mg ha− 1 for T. repens and L. perenne, respectively. The maximum amount of labile C in the T. repens sward was estimated at 8.3 ± 1.6 Mg ha− 1 and 7.1 ± 1.0 Mg ha− 1 in the L. perenne sward. Mean residence time (MRT) for newly sequestered soil C was estimated at 1.8 years in the T. repens plots and 1.1 years for L. perenne. An average of 18% of total soil C in the 0–10 cm depth in the T. repens sward and 24% in the L. perenne sward was derived from FACE after 6 years exposure. The majority of the change in soil δ13C occurred in the first three years of the experiment. No treatment effects on total soil C were detected.The fraction of FACE-derived C in the L. perenne sward was larger than in the T. repens sward. This suggests a priming effect in the L. perenne sward which led to increased losses of the old C. Although the rate of C cycling was affected by species and elevated CO2, the soil in this intensively managed grassland ecosystem did not become a sink for additional new C.

Notes: Under the Kyoto Protocol, the European Union is committed to a reduction in CO2 emissions to 92% of baseline (1990) levels during the first commitment period (2008–2012). The Kyoto Protocol allows carbon emissions to be offset by demonstrable removal of carbon from the atmosphere. Thus, land-use/land-management change and forestry activities that are shown to reduce atmospheric CO2 levels can be included in the Kyoto targets. These activities include afforestation, reforestation and deforestation (article 3.3 of the Kyoto Protocol) and the improved management of agricultural soils (article 3.4). In this paper, we estimate the carbon mitigation potential of various agricultural land-management strategies and examine the consequences of European policy options on carbon mitigation potential, by examining combinations of changes in agricultural land-use/land-management. We show that no single land-management change in isolation can mitigate all of the carbon needed to meet Europe's climate change commitments, but integrated combinations of land-management strategies show considerable potential for carbon mitigation. Three of the combined scenarios, one of which is an optimal realistic scenario, are by themselves able to meet Europe's emission limitation or reduction commitments. Through combined land-management scenarios, we show that the most important resource for carbon mitigation in agriculture is the surplus arable land. We conclude that in order to fully exploit the potential of arable land for carbon mitigation, policies will need to be implemented to allow surplus arable land to be put into alternative long-term land-use. Of all options examined, bioenergy crops show the greatest potential for carbon mitigation. Bioenergy crop production also shows an indefinite mitigation potential compared to other options where the mitigation potential is finite. We suggest that in order to exploit fully the bioenergy option, the infrastructure for bioenergy production needs to be significantly enhanced before the beginning of the first Kyoto commitment period in 2008. It is not expected that Europe will attempt to meet its climate change commitments solely through changes in agricultural land-use. A reduction in CO2-carbon emissions will be key to meeting Europe's Kyoto targets, and forestry activities (Kyoto Article 3.3) will play a major role. In this study, however, we demonstrate the considerable potential of changes in agricultural land-use and -management (Kyoto Article 3.4) for carbon mitigation and highlight the policies needed to promote these agricultural activities. As all sources of carbon mitigation will be important in meeting Europe's climate change commitments, agricultural carbon mitigation options should be taken very seriously.

Notes: Future increases in air temperature resulting from human activities may increase the water vapour pressure deficit (VPD) of the atmosphere. Understanding the responses of trees to spatial variation in VPD can strengthen our ability to predict how trees will respond to temporal changes in this important variable. Using published values, we tested the theoretical prediction that conifers decrease their investment in photosynthetic tissue (leaves) relative to water-conducting tissue in the stem (sapwood) as VPD increases. The ratio of leaf/sapwood area (AL/AS) decreased significantly with increasing VPD in Pinus species but not in Abies, Pseudotsuga, Tsuga and Picea, and the average AL/AS was significantly lower for pines than other conifers (pines: 0.17 m2 cm−2; nonpines: 0.44 m2 cm−2). Thus, pines adjusted to increasing aridity by altering above-ground morphology while nonpine conifers did not. The average water potential causing a 50% loss of hydraulic conductivity was −3.28 MPa for pines and −4.52 MPa for nonpine conifers, suggesting that pines are more vulnerable to xylem embolism than other conifers. For Pinus ponderosa the decrease in AL/AS with high VPD increases the capacity to provide water to foliage without escalating the risk of xylem embolism. Low AL/AS and plasticity in this variable may enhance drought tolerance in pines. However, lower AL/AS with increasing VPD and an associated shift in biomass allocation from foliage to stems suggests that pines may expend more photosynthate constructing and supporting structural mass and carry less leaf area as the climate warms.

Notes: Responses of leaf stomatal conductance to light, humidity and temperature were characterized for winter wheat and barely grown at ambient (about 350 μmol mol−1 in the daytime), ambient + 175 and ambient + 350 μmol mol−1 concentrations of carbon dioxide in open-topped chambers in field plots over a three year period. Stomatal responses to environment were determined by direct manipulation of single environmental factors, and those results were compared with responses derived from natural day to day variation in mid-day stomatal conductance. The purpose of these experiments was to determine the magnitude of reduction in stomatal conductance at elevated [CO2], and to assess whether the relative response of conductance to elevated [CO2] was constant across light, humidity and temperature conditions. The results indicated that light, humidity and temperature all significantly affected the relative decrease in stomatal conductance at elevated [CO2]. The relative decrease in conductance with elevated [CO2] was greater at low light, low water vapour pressure difference, and high temperature in both species. For measurements made at saturating light near mid-day, the ratio of mid-day stomatal conductances at doubled [CO2] to that at ambient [CO2] ranged from 0.42 to 0.86, with a mean of 0.66 in barley, and from 0.33 to 0.80, with a mean of 0.56 in wheat. Day-to-day variation in the relative effect of elevated [CO2] on conductance was correlated with the relative stimulation of [CO2] assimilation rate and with temperature. Some limitations of multiple linear regression, multiplicative, and ‘Ball–Berry' models as summaries of the data are discussed. In barley, a better fit to the models occurred in individual years than for the combined data, and in wheat a better fit to the models occurred when data from near the end of the season were removed.

Notes: Elevation of atmospheric CO2 concentration is predicted to increase net primary production, which could lead to additional C sequestration in terrestrial ecosystems. Soil C input was determined under ambient and Free Atmospheric Carbon dioxide Enrichment (FACE) conditions for Lolium perenne L. and Trifolium repens L. grown for four years in a sandy-loam soil. The 13C content of the soil organic matter C had been increased by 5‰ compared to the native soil by prior cropping to corn (Zea mays) for 〉 20 years. Both species received low or high amounts of N fertilizer in separate plots. The total accumulated above-ground biomass produced by L. perenne during the 4-year period was strongly dependent on the amount of N fertilizer applied but did not respond to increased CO2. In contrast, the total accumulated above-ground biomass of T. repens doubled under elevated CO2 but remained independent of N fertilizer rate. The C:N ratio of above-ground biomass for both species increased under elevated CO2 whereas only the C:N ratio of L. perenne roots increased under elevated CO2. Root biomass of L. perenne doubled under elevated CO2 and again under high N fertilization. Total soil C was unaffected by CO2 treatment but dependent on species. After 4 years and for both crops, the fraction of new C (F-value) under ambient conditions was higher (P= 0.076) than under FACE conditions: 0.43 vs. 0.38. Soil under L. perenne showed an increase in total soil organic matter whereas N fertilization or elevated CO2 had no effect on total soil organic matter content for both systems. The net amount of C sequestered in 4 years was unaffected by the CO2 concentration (overall average of 8.5 g C kg−1 soil). There was a significant species effect and more new C was sequestered under highly fertilized L. perenne. The amount of new C sequestered in the soil was primarily dependent on plant species and the response of root biomass to CO2 and N fertilization. Therefore, in this FACE study net soil C sequestration was largely depended on how the species responded to N rather than to elevated CO2.

Notes: Recent strong El Niño-Southern Oscillation (ENSO) signals have been identified in precipitation records from the Iberian Peninsula. Interannual association with ENSO accounts for more than half the total annual variance in selected stations of the south-east, with ENSO leading rainfall by one year. In contrast, association with the North Atlantic Oscillation (NAO) at the Westernmost stations is much lower (25%). The potential of simple linear models is tested in the ENSO-sensitive area, suggesting high capability of the Southern Oscillation Index (SOI) for predicting interannual rainfall fluctuations (mainly droughts and floods). Wine quality is associated with several factors, e.g. grape variety, soil type and processing, which can be considered invariable, mainly due to the strict regulations imposed by the quality regulating councils. Climate, however, has a great influence on resulting wine quality, and represents the most important source of variability at both short (day-to-day) and long (interannual) time scales.Over the last 30 years, high-quality harvests in the five main wine regions in Spain, show a high probability (P 〈 0.0002) of being associated with an El Niño event occurring the same year or the year before. NAO influence is not significant during the same period. Thus, apart from considering the role of local climatic conditions in certain regions, which favour the production of excellent wines, larger-scale climatic phenomena appear responsible for the year-to-year variations in quality.

Notes: When agricultural land is no longer used for cultivation and allowed to revert to natural vegetation or replanted to perennial vegetation, soil organic carbon can accumulate. This accumulation process essentially reverses some of the effects responsible for soil organic carbon losses from when the land was converted from perennial vegetation. We discuss the essential elements of what is known about soil organic matter dynamics that may result in enhanced soil carbon sequestration with changes in land-use and soil management. We review literature that reports changes in soil organic carbon after changes in land-use that favour carbon accumulation. This data summary provides a guide to approximate rates of SOC sequestration that are possible with management, and indicates the relative importance of some factors that influence the rates of organic carbon sequestration in soil. There is a large variation in the length of time for and the rate at which carbon may accumulate in soil, related to the productivity of the recovering vegetation, physical and biological conditions in the soil, and the past history of soil organic carbon inputs and physical disturbance. Maximum rates of C accumulation during the early aggrading stage of perennial vegetation growth, while substantial, are usually much less than 100 g C m−2 y−1. Average rates of accumulation are similar for forest or grassland establishment: 33.8 g C m−2 y−1 and 33.2 g C m−2 y−1, respectively. These observed rates of soil organic C accumulation, when combined with the small amount of land area involved, are insufficient to account for a significant fraction of the missing C in the global carbon cycle as accumulating in the soils of formerly agricultural land.

Notes: Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies Karst.) seedlings were exposed to realistically elevated O3 levels in open-air experiments over three growing seasons. The total O3 exposure doses were 1.2 × (1991), 1.5 × (1992) and 1.7 × (1993) ambient levels. During the 1992 and 1993 growing seasons pine and spruce seedlings received two different levels of nitrogen supply. Effects on growth, mycorrhiza formation, needle ultrastructure, primary and secondary compounds were studied. Ozone exposure had only slight effects on biomass production, growth height and nutrient content of studied conifers. Higher nitrogen availability improved growth of the seedlings and resulted in higher concentration of nitrogen in needles. In Scots pine O3 exposure did not have effects on quantity of total mycorrhizas and short roots, while higher nitrogen availability decreased quantity of mycorrhizas and short roots. In both tree species O3 exposure induced O3-related ultrastructural symptoms, e.g. granulation and dark staining of the chloroplast stroma in the needle mesophyll cells, at both nitrogen availability levels. Ozone exposure and nitrogen availability did not have significant effects on starch concentrations in either tree species. Concentrations of some individual terpenes were higher in O3-exposed needles, while concentrations of individual and total resin acids, total phenolics and catechins were not affected by O3 exposure. Nitrogen availability did not have substantial effects on concentrations of monoterpenes. By contrast, concentrations of some individual and total resin acids were lower in pine needles and higher in spruce needles with higher nitrogen availability, while phenolic concentration in spruce needles decreased at higher nitrogen availability. The results suggest that realistically elevated levels of O3 in the field can have some negative effects on the mesophyll ultrastructure of conifer needles, but carbon allocation to root and shoot growth and secondary metabolites are not affected substantially.

Notes: The phenological and physiological responses of arctic tundra plant species are key to predicting their survival in a warmer climate. One of the consequences of a warmer climate in the Arctic will be a longer growing season. We examined the effects of lengthened growing season and soil warming on the widely distributed forb, Polygonum bistorta L. Three treatments were established near Toolik Lake, Alaska in 1995 and 1996: extended season, extended season with soil warming, and an unmanipulated control. The season was extended by removing the snow load in the spring and keeping the treatments free of snow in the autumn. The spring snow removal extended the snow-free period over that of controls by 8 d in 1995 and 24 d in 1996. As a result, the number of accumulated soil thaw days and consequently the depth of soil thaw increased on the treatment plots. Polygonum bistorta responded to the treatments by becoming active earlier and senescing earlier, resulting in a growth period of similar duration to that of the controls. Leaf size and leaf number were unaffected by the treatments, as were leaf photosynthetic assimilation rates and nutrient concentrations. The results indicate that internal constraints limit the response of this species to lengthened growing season, suggesting that it is a determinant or periodic species. With climate warming, this periodic growth will put P. bistorta at a competitive disadvantage relative to plants that can respond to lengthened growing season.

Notes: Nitrogen-stressed microcosms of the C3 grass Danthonia richardsonii gained nitrogen from the environment when grown under ambient or enriched (359, ‘amb’ or 719 μL L− 1‘enr’, respectively) atmospheric CO2 concentrations over a 4-y period. This gain was apparent at all rates of supplied mineral N (2.2, 6.7 or 19.8 g N m− 2 y− 1– low-N, mid-N or high-N), although it was small at high-N. Small losses of N occurred from the microcosm as leachate, while gaseous losses of N were estimated to be between 10% and 25% of applied mineral N. Losses of applied mineral N were slightly lower under CO2 enrichment only at the highest rate of mineral N supply. Levels of 15N natural abundance in green leaf (δ15Ν) of − 2‰ (amb low-N) and of below − 4‰ (enr low- & mid-N) suggest that absorption of atmospheric NH3 may have been a source of some of the extra N in the low and mid-N treatments. Biological N2 fixation, of up to 2 g m− 2 y− 1 was hypothesized to form the remainder of the environmental N source. Microcosm C:N ratio was higher under CO2 enrichment. Nitrogen productivity of microcosm carbon gain (g C accumulated g− 1 leaf N day− 1) was increased (up to 100%) by CO2 enrichment at all rates of mineral N supply. Green leaf %N was reduced by CO2 enrichment, and there was less nitrogen in the green leaf pool under CO2 enrichment. Less, or the same amount of nitrogen was present in senesced leaf, surface litter and root under CO2 enrichment while more nitrogen was present in the soil in organic forms, and as NH4 +  at the highest rate of mineral N supply.

Notes: Litter quality parameters of Danthonia richardsonii grown under CO2 concentrations of ≈ 359 & ≈ 719 μL L− 1 at three mineral N supply rates (2.2, 6.7 & 19.8 g m− 2 y− 1) were determined. C:N ratio was increased in senesced leaf (enhancement ratios, Re/c, of 1.25–1.67), surface litter (1.34–1.64) and root (1.13–1.30) by CO2 enrichment. After 3 years of growth, nonstructural carbohydrate concentrations were reduced in senesced leaf lamina (avg. Re/c=  0.84) but not in root in response to CO2 enrichment. Cellulose concentrations increased slightly in senesced leaf (avg. Re/c=  1.07) but not in root in response to CO2 enrichment. Lignin and polyphenolic concentrations in senesced leaf and root were not changed by CO2 enrichment. Decomposition, measured as cumulative respiration in standard conditions in vitro, was reduced in leaf litter grown under CO2 enrichment. Root decomposition in vitro was lower in the material produced under CO2 enrichment at the two higher rates of mineral N supply. Significant correlations between decomposition of leaf litter and initial %N, C:N ratio and lignin:N ratio were found. Decomposition in vivo, measured as carbon disappearance from the surface litter was not affected by CO2 concentration. Arbuscular mycorrhizal infection was not changed by CO2 enrichment. Microbial carbon was higher under CO2 enrichment at the two higher rates of mineral N supply. Possible reasons for the lack of effect of changes in litter quality on in-sward decomposition rates are discussed.

Notes: We have used satellite colour data to classify ocean environments for monitoring interannual changes in the ocean. The unsupervised classification method is based on our observation that the frequency distributions of Coastal Zone Color Scanner (CZCS) annual pigment means and standard deviations are nonuniform and contain distinct clusters. The frequency distributions are used to objectively determine ocean areas with similar pigment statistical characteristics. A major separation between high variance, high pigment and lower variance, lower pigment waters is observed in terms of global ocean area. The ocean areas determined with our method reflect different bio-logical responses to variations in ocean physical dynamics. Pigment means and variances around the Joint Global Ocean Flux Study (JGOFS) Time Series stations are used as fiducial characteristics. Hawaii Ocean Time-series (HOT) station is associated with the low-variance portion of the global annual pigment distribution characteristic of the central gyres, but shows slightly higher mean and variance than the minima in the central Pacific gyre. The Bermuda Atlantic Time Series (BATS) pigment associations comprise a transitional region between the gyres and high-variance pigment areas, and circumscribe the HOT pigment associations. Together, these associations encompass 23% (HOT-like) and 48% (BATS-like) of the Northern Hemisphere open ocean. The Pacific regions delineated by the JGOFS station pigment-based patterns are similar to distributions described historically for Pacific zooplankton communities. Interannual variation for the northern hemisphere gyre area is on the order of by 10% for the 11/78–10/81 period.

Notes: The effects of low-level ozone exposure and suppression of natural mycorrhizas on the above-ground chemical quality of Scots pine (Pinus sylvestris L.) needles and insect herbivore performance were studied in a two-year field experiment. Seedlings were fumigated with the ozone doses 1.5–1.7 times the ambient, and natural mycorrhizal infection level was about 35% reduced in roots with fungicide propiconazole. On ozone-exposed seedlings the mean relative growth rate (MRGR) of Lygus rugulipennis Popp. nymphs was lower than on ambient ozone seedlings, but Gilpinia pallida Klug sawfly larvae grew better on elevated ozone seedlings than on ambient ozone seedlings. MRGR of Schizolachnus pineti Fabr. and Cinara pinea L. aphid nymphs or Neodiprion sertifer Geoffr. sawfly larvae or the oviposition of L. rugulipennis and N. sertifer were not affected by ozone exposure. Although ozone exposure did not affect total phenolics, total terpene, total or individual resin acid, total free amino acid, nutrient or sugar concentrations in needles, MRGR of L. rugulipennis positively correlated with total terpenes and MRGR of G. pallida positively with total amino acids. In addition, ozone exposure increased serine and proline concentration and marginally also starch concentration in needles. When mycorrhizas were reduced with fungicide, only MRGR of L. rugulipennis nymphs increased, but performance of other insect herbivores studied was not changed. However, number of L. rugulipennis eggs correlated positively with mycorrhizal infection level and also with total sugars. Reduction of mycorrhizas did not strongly affect the concentrations of analysed compounds in needles, because only phosphorus and potassium and some individual resin acids were reduced by fungicide treatment. These results suggest that low-level ozone exposure and moderately declined mycorrhizal infection do not drastically affect either the above-ground chemical quality of Scots pine seedlings or performance of studied insect herbivores.

Notes: The sensitivity of a global biome model (BIOME3) to uncertainty in parameter values was investigated by testing the model's sensitivity to minimum and maximum parameter values obtained from an extensive literature search. Simulations were conducted replacing the default parameter value by each of the maximum and minimum values determined from the literature. In doing so, the aim was to identify those parameters where the use of an alternate (observed) value leads to a significant change in the simulation of plant functional types at a global scale, in order to identify those which are functionally important to the model. BIOME3 was found to be insensitive to changes in the majority of its parameters, providing a generally sound foundation for confidence in model simulations. However, there was considerable sensitivity shown to over a quarter of the parameters. Three main types of parameters led to a change in plant functional types distribution relative to the control simulation: (i) parameters affecting the photosynthesis parameterization; (ii) parameters affecting the evapotranspiration parameterization; and (iii) root distribution which affected both parts of the model. The main causes of sensitivity were changes in the photosynthesis parameters leading to differential changes in plant functional type's net primary productivity. This caused a shift in the competitive balance between specific plant functional types or between C3 and C4 plant types, and a consequent change in their global distribution. Changes to the evapotranspiration parameters and root distribution similarly affected net primary productivity and soil moisture, and often led to shifts in the competitive balance between grass and trees. Changes in the value for several poorly known parameters produced substantial changes in the distribution of plant functional types, and reduced the κ-statistic to a large degree, indicating areas of potential uncertainty in the model. This suggests that great care must be taken in prescribing values to these parameters and provides guidance on which parameters need further attention in observational work.

Notes: Plant responses to elevated atmospheric CO2 have been characterized generally by stomatal closure and enhanced growth rates. These responses are being increasingly incorporated into global climate models that quantify interactions between the biosphere and atmosphere, altering climate predictions from simpler physically based models. However, current information on CO2 responses has been gathered primarily from studies of crop and temperate forest species. In order to apply responses of vegetation to global predictions, CO2 responses in other commonly occurring biomes must be studied. A Free Air CO2 Enrichment (FACE) study is currently underway to examine plant responses to high CO2 in a natural, undisturbed Mojave Desert ecosystem in Nevada, USA. Here we present findings from this study, and its companion glasshouse experiment, demonstrating that field-grown Ephedra nevadensis and glasshouse-grown Larrea tridentata responded to high CO2 with reductions in the ratio of transpirational surface area to sapwood area (LSR) of 33% and 60%, respectively. Thus, leaf-specific hydraulic conductivity increased and stomatal conductance remained constant or was increased under elevated CO2. Field-grown Larrea did not show a reduced LSR under high CO2, and stomatal conductance was reduced in the high CO2 treatment, although the effect was apparent only under conditions of unusually high soil moisture. Both findings suggest that the common paradigm of 20–50% reductions in stomatal conductance under high CO2 may not be applicable to arid ecosystems under most conditions.

Notes: Soybean (Glycine max) was grown at ambient and enhanced carbon dioxide (CO2, + 250 μL L−1 above ambient) with and without the presence of a C3 weed (lambsquarters, Chenopodium album L.) and a C4 weed (redroot pigweed, Amaranthus retroflexus L.), in order to evaluate the impact of rising atmospheric carbon dioxide concentration [CO2] on crop production losses due to weeds. Weeds of a given species were sown at a density of two per metre of row. A significant reduction in soybean seed yield was observed with either weed species relative to the weed-free control at either [CO2]. However, for lambsquarters the reduction in soybean seed yield relative to the weed-free condition increased from 28 to 39% as CO2 increased, with a 65% increase in the average dry weight of lambsquarters at enhanced [CO2]. Conversely, for pigweed, soybean seed yield losses diminished with increasing [CO2] from 45 to 30%, with no change in the average dry weight of pigweed. In a weed-free environment, elevated [CO2] resulted in a significant increase in vegetative dry weight and seed yield at maturity for soybean (33 and 24%, respectively) compared to the ambient CO2 condition. Interestingly, the presence of either weed negated the ability of soybean to respond either vegetatively or reproductively to enhanced [CO2]. Results from this experiment suggest: (i) that rising [CO2] could alter current yield losses associated with competition from weeds; and (ii) that weed control will be crucial in realizing any potential increase in economic yield of agronomic crops such as soybean as atmospheric [CO2] increases.

Notes: We propose that elevated CO2 may have a significant positive effect on woody plant success and thus favour tree invasion and thickening in grass-dominated ecosystems. We note that savanna tree biomass is strongly constrained by disturbance, particularly fire, and that elevated CO2 could act to reduce this constraint. Our argument combines knowledge of tree recovery from injury after grassland fires, with theory about carbon acquisition and carbohydrate storage patterns in C3 woody plants in response to elevated CO2. We propose simply that elevated CO2 will tend to favour regrowth of juvenile trees trapped (sometimes for decades) in the ‘topkill’ zone, thus allowing them to escape more readily from periodic fires as CO2 continues to rise. Little empirical evidence exists to test this hypothesis, even though the process may have important implications for tree/grass codominated ecosystems currently in a dynamic equilibrium.

Notes: The effect of elevated CO2 on photosynthesis, respiration, and growth efficiency of sunflower plants at the whole-stand level was investigated using a whole-system gas exchange facility (the EcoCELLs at the Desert Research Institute) and a 13C natural tracer method. Total daily photosynthesis (GPP), net primary production (NPP), and respiration under the elevated CO2 treatment were consistently higher than under the ambient CO2 treatment. The overall level of enhancement due to elevated CO2 was consistent with published results for a typical C3 plant species. The patterns of daily GPP and NPP through time approximated logistic curves under both CO2 treatments. Regression analysis indicated that both the rate of increase (the parameter ‘r’) and the maximum value (the parameter ‘k’) of daily GPP and NPP under the elevated CO2 treatment were significantly higher than under the ambient CO2 treatment. The percentage increase in daily GPP due to elevated CO2 varied systematically through time according to the logistic equations used for the two treatments. The GPP increase due to elevated CO2 ranged from approximately 10% initially to 73% at the peak, while declining to about 33%, as predicted by the ratio of the two maximum values. Different values of percentage increase in GPP and NPP were obtained at different sampling times. This result demonstrated that one-time measurements of percentage increases due to elevated CO2 could be misleading, thereby making interpretation difficult. Although rhizosphere respiration was substantially enhanced by elevated CO2, no effect of elevated CO2 on R:P (respiration:photosynthesis) was found, suggesting an invariant NPP:GPP ratio during the entire experiment. Further validation of the notion of an invariant NPP:GPP ratio may significantly simplify the process of quantifying terrestrial carbon sequestration by directly relating total photosynthesis to net primary production.

Notes: We investigated the effects of elevated atmospheric CO2 concentrations (ambient + 200 ppm) on fine root production and soil carbon dynamics in a loblolly pine (Pinus taeda) forest subject to free-air CO2 enrichment (FACE) near Durham, NC (USA). Live fine root mass (LFR) showed less seasonal variation than dead fine root mass (DFR), which was correlated with seasonal changes in soil moisture and soil temperature. LFR mass increased significantly (by 86%) in the elevated CO2 treatment, with an increment of 37 g(dry weight) m−2 above the control plots after two years of CO2 fumigation. There was no long-term increment in DFR associated with elevated CO2, but significant seasonal accumulations of DFR mass occurred during the summer of the second year of fumigation. Overall, root net primary production (RNPP) was not significantly different, but annual carbon inputs were 21.7 gC m−2 y−1 (68%) higher in the elevated CO2 treatment compared to controls. Specific root respiration was not altered by the CO2 treatment during most of the year; however, it was significantly higher by 21% and 13% in September 1997 and May 1998, respectively, in elevated CO2. We did not find statistically significant differences in the C/N ratio of the root tissue, root decomposition or phosphatase activity in soil and roots associated with the treatment. Our data show that the early response of a loblolly pine forest ecosystem subject to CO2 enrichment is an increase in its fine root population and a trend towards higher total RNPP after two years of CO2 fumigation.

Notes: Particulate pollution is a serious health problem throughout the world, exacerbating a wide range of respiratory and vascular illnesses in urban areas. The use of trees to reduce the effects of these pollutants has been addressed in the literature, but has rarely been quantified. The aim of the present study was to quantify the effectiveness of five tree species − pine (Pinus nigra var. maritima), cypress ( × Cupressocyparis leylandii), maple (Acer campestre), whitebeam (Sorbus intermedia), poplar (Populus deltoides × trichocarpa‘Beaupré’) − in capturing pollutant particles. This was achieved by exposing them to NaCl droplets of approximately 1 μm diameter at a range of windspeeds in two windtunnels. The deposition velocity (Vg) and particle trapping efficiency (Cp) were calculated from these exposures. In addition, a variable dependent on foliage structure [Stokes number (St)] was correlated with Cp to gauge the effect of tree morphology on particle capture. Maximum Cp values ranged from 2.8% for P. nigra, to 0.12% and 0.06% for P. trichocarpa×deltoides and A. campertre, respectively. The finer, more complex structure of the foliage of the two conifers (P. nigra and C. leylandii) explained their much greater effectiveness at capturing particles. The data presented here will be used to model the effectiveness of tree planting schemes in improving urban air quality by capturing pollutant particles.

Notes: We analysed data on mass loss after five years of decomposition in the field from both fine root and leaf litters from two highly contrasting trees, Drypetes glauca, a tropical hardwood tree from Puerto Rico, and pine species from North America as part of the Long-Term Intersite Decomposition Experiment (LIDET). LIDET is a reciprocal litterbag study involving the transplanting of litter from 27 species across 28 sites in North and Central America reflecting a wide variety of natural and managed ecosystems and climates, from Arctic tundra to tropical rainforest. After 5 years, estimated k-values ranged from 0.032 to 3.734, lengths of Phase I (to 20% mass remaining) from 0.49 to 47.92 years, and fractional mass remaining from 0 to 0.81. Pine litter decomposed more slowly than Drypetes litter, supporting the notion of strong control of substrate quality over decomposition rates. Climate exerted strong and consistent effects on decomposition. Neither mean annual temperature or precipitation alone explained the global pattern of decomposition; variables including both moisture availability and temperature (i.e. actual evapotranspiration and DEFAC from the CENTURY model) were generally more robust than single variables. Across the LIDET range, decomposition of fine roots exhibited a Q10 of 2 and was more predictable than that of leaves, which had a higher Q10 and greater variability. Roots generally decomposed more slowly than leaves, regardless of genus, but the ratio of above- to belowground decomposition rates differed sharply across ecosystem types. Finally, Drypetes litter decomposed much more rapidly than pine litter in ‘broadleaved habitats’ than in ‘conifer habitats’, evidence for a ‘home-field advantage’ for this litter. These results collectively suggest that relatively simple models can predict decomposition based on litter quality and regional climate, but that ecosystem-specific problems may add complications.