Field Evidence for Optimal Acclimation of Leaf Nitrogen to Environmental Gradients

Abstract:

Nitrogen per unit leaf area (N_area) is a key variable in plant functional ecology and biogeochemistry. We hypothesized that N_area should be sum of a structural component proportional to leaf mass per area (LMA) and a metabolic component, predicted by optimality considerations to be proportional to irradiance while decreasing with air-to-leaf carbon dioxide drawdown (c_i:c_a) and temperature. The significant partial environmental and LMA effects on N_area that are both qualitatively and quantitatively supported this hypothesis by using LMA, leaf δ¹³C and N_area measurements on transcontinental transect in Australia. Trait gradient analysis revealed c_i:c_a to be perfectly plastic, while species turnover contributed about half the variation in LMA and N_area, consistent with a strong contribution of species turnover to the variation of these traits with environment. These findings motivate a hybrid leaf-economics approach to the prediction of N_area in ecosystem models.