Global effects of soil and climate on leaf photosynthetic traits and rates

AimThe 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. LocationTerrestrial ecosystems world-wide. MethodsUsing 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 (A(area)), stomatal conductance (g(s)), leaf nitrogen and phosphorus (N-area and P-area) and specific leaf area (SLA) using mixed regression models and multivariate analyses. ResultsSoil variables were stronger predictors of leaf traits than climatic variables, except for SLA. On average, N-area, P-area and A(area) increased and SLA decreased with increasing soil pH and with increasing site aridity. g(s) declined and P-area increased with soil available P (P-avail). N-area was unrelated to total soil N. Joint effects of soil and climate dominated over their unique effects on N-area and P-area, while unique effects of soils dominated for A(area) and g(s). Path analysis indicated that variation in A(area) reflected the combined independent influences of N-area and g(s), the former promoted by high pH and aridity and the latter by low P-avail. Main conclusionsThree environmental variables were key for explaining variation in leaf traits: soil pH and P-avail, 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.