Data from: Global effects of soil and climate on leaf photosynthetic traits and rates

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.