Browsing by Author "Ellsworth, David"

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    Global effects of soil and climate on leaf photosynthetic traits and rates
    (Wiley, 2015) Maire, Vincent; Wright, Ian J; Prentice, I. Colin; Batjes, Niels H; Bhaskar, Radika; Bodegom, Peter M; Cornwell, Will K; Ellsworth, David; Niinemets, Ülo; Ordonez, Alejandro; Reich, Peter B; Santiago, Louis S
    Aim The influence of soil properties on photosynthetic traits in higher plants is poorly quantified in comparison with that of climate. We address this situation by quantifying the unique and joint contributions to global leaf-trait variation from soils and climate. Location Terrestrial ecosystems world-wide. Methods Using a trait dataset comprising 1509 species from 288 sites, with climate and soil data derived from global datasets, we quantified the effects of 20 soil and 26 climate variables on light-saturated photosynthetic rate (Aarea), stomatal conductance (gs), leaf nitrogen and phosphorus (Narea and Parea) and specific leaf area (SLA) using mixed regression models and multivariate analyses. Results Soil variables were stronger predictors of leaf traits than climatic variables, except for SLA. On average, Narea, Parea and Aarea increased and SLA decreased with increasing soil pH and with increasing site aridity. gs declined and Parea increased with soil available P (Pavail). Narea was unrelated to total soil N. Joint effects of soil and climate dominated over their unique effects on Narea and Parea, while unique effects of soils dominated for Aarea and gs. Path analysis indicated that variation in Aarea reflected the combined independent influences of Narea and gs, the former promoted by high pH and aridity and the latter by low Pavail. Main conclusions Three environmental variables were key for explaining variation in leaf traits: soil pH and Pavail, and the climatic moisture index (the ratio of precipitation to potential evapotranspiration). Although the reliability of global soil datasets lags behind that of climate datasets, our results nonetheless provide compelling evidence that both can be jointly used in broad-scale analyses, and that effects uniquely attributable to soil properties are important determinants of leaf photosynthetic traits and rates. A significant future challenge is to better disentangle the covarying physiological, ecological and evolutionary mechanisms that underpin trait–environment relationships.
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    Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition
    (Nature Publishing Group, 2001) Reich, Peter B; Knops, Jean; Tilman, David; Craine, Joseph; Ellsworth, David; Tjoelker, Mark; Lee, Tali; Wedin, David; Naeem, Shahid; Bahauddin, Dan; Hendrey, George; Jose, Shibu; Wrage, Keith; Goth, Jenny; Bengston, Wendy
    Human actions are causing declines in plant biodiversity, increases in atmospheric CO2 concentrations and increases in nitrogen deposition; however, the interactive effects of these factors on ecosystem processes are unknown1, 2. Reduced biodiversity has raised numerous concerns, including the possibility that ecosystem functioning may be affected negatively1, 2, 3, 4, which might be particularly important in the face of other global changes5, 6. Here we present results of a grassland field experiment in Minnesota, USA, that tests the hypothesis that plant diversity and composition influence the enhancement of biomass and carbon acquisition in ecosystems subjected to elevated atmospheric CO2 concentrations and nitrogen deposition. The study experimentally controlled plant diversity (1, 4, 9 or 16 species), soil nitrogen (unamended versus deposition of 4 g of nitrogen per m2 per yr) and atmospheric CO2 concentrations using free-air CO2 enrichment (ambient, 368 micromol mol-1, versus elevated, 560 micromol mol-1). We found that the enhanced biomass accumulation in response to elevated levels of CO2 or nitrogen, or their combination, is less in species-poor than in species-rich assemblages.