Soil nitrogen supply exerts largest influence on leaf nitrogen in
environments with the greatest leaf nitrogen demand
Abstract
Accurately representing the relationships between nitrogen supply and
photosynthesis is crucial for reliably predicting carbon-nitrogen cycle
coupling in Earth System Models (ESMs). Most ESMs assume positive
correlations among soil nitrogen supply, leaf nitrogen content, and
photosynthetic capacity. However, leaf photosynthetic nitrogen demand
may influence the leaf nitrogen response to soil nitrogen supply, thus
responses to nitrogen supply are expected to be largest in environments
where demand is greatest. Using a nutrient addition experiment
replicated at 26 sites spanning four continents, we demonstrated that
climate variables were stronger predictors of leaf nitrogen content than
soil nutrient supply. Leaf nitrogen increased more strongly with soil
nitrogen supply in regions with highest theoretical leaf nitrogen
demand, increasing more in colder and drier environments than warmer and
wetter ones. Thus, leaf nitrogen responses to nitrogen supply are
primarily influenced by climatic gradients in photosynthetic nitrogen
demand, an insight that will improve ESM predictions.