ALBERT

Description: Questions How does fine-scale soil heterogeneity impact on co-occurring species? Which species are advantaged in heterogeneous soils? Location Greenhouse experiment using European grassland species, University of Tartu, Estonia. Methods We grew plant assemblages consisting of 15 species in five soil treatments – comprising three spatially uniform fertility levels (low, medium or high) and two heterogeneous conditions created using checkerboard combinations of low- and high-fertility patches at two spatial scales (6.25 × 6.25 cm or 12.5 × 12.5 cm patches, overall medium fertility). We compared species responses (above-ground biomass) between heterogeneous and homogeneous treatments. Additionally, we compared species responses within low-fertility patches in heterogeneous treatments to the homogeneous treatment of the same fertility. Results Larger, dominant species were advantaged in heterogeneous compared to homogeneous conditions (with the same or lower overall fertility), whereas the growth and survival of smaller, subordinate species was reduced. Larger, dominant species also had increased above-ground biomass within the low-fertility patches in heterogeneous compared to homogeneous low-fertility conditions, but the opposite was true for smaller, subordinate species. In general, species responses in heterogeneous conditions did not differ from the homogeneous high-fertility treatment, although the heterogeneous conditions had lower overall fertility. Conclusions In our experimental grasslands, species differed in their responses to fine-scale soil heterogeneity. Patchy resource distribution directly benefits larger, dominant species that can forage among patches and produce more above-ground biomass compared to conditions where the same amount of resources is distributed homogeneously. Smaller, subordinate species that are more likely confined to a uniform soil patch are disadvantaged by heterogeneity due to increased root and shoot competition from neighbouring species. These species-specific responses to fine-scale soil heterogeneity and altered competitive interactions have important implications for plant community structure and productivity. Soil heterogeneity can alter community structure if some species benefit more from heterogeneity than others. In experimental grassland communities, larger species foraged among patches in heterogeneous soils and produced more biomass compared to homogeneous conditions. Smaller species were disadvantaged in heterogeneous soils due to stronger competition. Fine-scale soil heterogeneity affects plant growth and species interactions, ultimately determining community structure.

Description: Coral reefs are threatened worldwide, and there is a need to develop new approaches to monitor reef health under natural conditions. Because simultaneous measurements of net community production (NCP) and net community calcification (NCC) are used as important indicators of reef health, tools are needed to assess them in situ . Here, we present the Benthic Ecosystem and Acidification Measurement System (BEAMS), to provide the first fully autonomous approach capable of sustained, simultaneous measurements of reef NCP and NCC under undisturbed, natural conditions on timescales ranging from tens of minutes to weeks. BEAMS combines the chemical and velocity gradient in the benthic boundary layer to quantify flux from the benthos for a variety of parameters to measure NCP and NCC. Here, BEAMS was used to measure these rates from two different sites with different benthic communities on the western reef terrace at Palmyra Atoll for two weeks in September, 2014. Measurements were made every ∼15 minutes. The trends in metabolic rates were consistent with the benthic communities between the two sites with one dominated by fleshy organisms and the other dominated by calcifiers (degraded and healthy reefs, respectively). This demonstrates the potential utility of BEAMS as a reef health monitoring tool. NCP and NCC were tightly coupled on timescales of minutes to days, and light was the primary driver for the variability of daily integrated metabolic rates. No correlation between CO 2 levels and daily integrated NCC was observed, indicating that NCC at these sites were not significantly affected by CO 2 . This article is protected by copyright. All rights reserved.

Description: Questions Predicted increases in temperature and changes to precipitation are expected to alter the amount of plant available nutrients, in turn, altering rates of primary production and exotic plant invasions. However, it remains unclear whether increased responses occur in wetter than average years, even in low fertility and low rainfall regions. Location Four Australian grasslands, including sites in arid Western Australia, semi-arid Victoria, alpine Victoria and sub-tropical Queensland. Methods Using identical nutrient addition experiments, we use 6-years of biomass, cover and species richness data to examine how rates of biomass production and native and exotic cover and richness are affected by growing season precipitation [proportion of yearly growing season precipitation (GSP) to long-term mean GSP] and nutrient (N, P, K and micronutrients) addition. Results Rates of grassland productivity strongly increased with increasing GSP. GSP increased rates of native cover but not native or exotic richness, nor rates of exotic cover change. We detected no significant NPK effect on rates of grassland productivity, exotic cover or exotic richness change. In contrast, NPK addition decreased rates of native cover change and fertilized plots had significantly fewer native species. We did not detect a significant interaction between NPK and GSP . Conclusions Grassland productivity was more strongly predicted by variation in growing season precipitation than by nutrient addition, suggesting it will vary with future changes in rainfall. Response to nutrients, however, depend on species origin, suggesting that increasing soil nutrient availability due to anthropogenic activities is likely to lead to negative effects on native species richness and cover. How nutrients effect species composition and productivity in grasslands depends on species origin and precipitation. We show in four Australian grasslands that native species richness generally responds negatively to nutrient addition, but grassland productivity is positively associated with growing season precipitation. These findings suggest that modelling of grassland ecosystem response to global change drivers is sensitive to evolutionary history.

Description: Researchers have long noted the potential for shallow hydrothermal fluids to perturb near-surface temperatures. Several investigators have made qualitative or semi-quantitative use of elevated surface temperatures; for example, in snowfall calorimetry, or for tracing subsurface flow paths. However, a quantitative framework connecting surface temperature observations with conditions in the subsurface is currently lacking. Here, we model an area of shallow subsurface flow at Burgdorf Hot Springs, a rustic commercial resort in the Payette National Forest, north of McCall, Idaho USA. We calibrate the model using shallow (0.2 m depth) ground temperature measurements and overburden thickness estimates from seismic refraction studies. The calibrated model predicts negligible loss of heat energy from the laterally-migrating fluids at the Burgdorf site, in spite of the fact that thermal anomalies are observed in the unconsolidated near-surface alluvium. Although elevated near-surface ground temperatures are commonly assumed to result from locally high heat flux, this conflicts with the small apparent heat loss during lateral flow inferred at the Burgdorf site. We hypothesize an alternative explanation for near-surface temperature anomalies that is only weakly dependent on heat flux, and more strongly controlled by the Biot number, a dimensionless parameter that compares the rate at which convection carries heat away from the land surface to the rate at which it is supplied by conduction to the interface.

Description: Question There are contrasting opinions about how communities assemble along a productivity gradient, particularly in relation to competitive interactions. One view is that functionally similar, and closely related species, are less likely to co-exist (limiting similarity). Alternatively, competitive exclusion may act on dissimilar species because species bearing traits associated with low competitive ability are excluded (weaker competitor exclusion). We ask if patterns of functional and phylogenetic diversity are related to changes in species diversity in response to fertility manipulations. Location Species-rich mesophytic grassland in Estonia. Methods The grassland has been manipulated from 2002 to 2011 to increase (fertilizer addition) and decrease productivity (sucrose addition) in small-scale (50 cm × 50 cm) plots. We linked annual increases and decreases in species diversity to changes in functional and phylogenetic diversity. We used abundance-weighted mean pair-wise functional or phylogenetic distance of all possible species pairs. Results We found convergence in four traits (plant height, leaf distribution, lateral spread, type of reproduction) and a decrease in mean functional and phylogenetic diversity, in support of weaker competitor exclusion or habitat filtering. There was less support for limiting similarity, with divergence found for two traits associated with decreasing species diversity (leaf distribution in the sucrose treatment and lateral spread in the fertilizer treatment). Conclusions Our results support the view that competition can lead to the exclusion of weaker competitors, rather than increasing functional and phylogenetic diversity, as expected from the principle of limiting similarity. However, multiple assembly processes, which are generally seen as mutually exclusive, are operating simultaneously, albeit on different traits and at different stages of community assembly. We used a long-term resource manipulation experiment to determine patterns of trait diversity and phylogenetic relatedness in relation to changes in species diversity to test the idea that competitive exclusion acts on the most similar coexisting species. We found mostly a reduction in functional and phylogenetic diversity associated with species loss indicating that species more dissimilar are excluded particularly following fertilization.