Zhengbing Yan, Xiuping Li, Di Tian, Wenxuan Han, Xinghui Hou, Haihua Shen, Yalong Guo, Jingyun Fang
As two essential mineral elements in biological organisms, availability of nitrogen (N) and phosphorus (P) frequently constrains plant growth and primary productivity across numerous ecosystems. Given the functionally coupled links between N and P, their concentrations in leaves are often closely related. Ambient nutrient changes influence the coupling of N and P in terrestrial ecosystems, but whether they could alter the scaling relationship of plant leaf N to P concentrations remains unclear. Here we conducted experimental manipulations using the annual plant Arabidopsis thaliana, with five levels of N and P additions and nine repeated experiments, and then evaluated the changes in the scaling relationship of leaf N to P concentrations under nutrient additions. Our data show for the first time that the scaling relationship of leaf N to P concentrations is largely modulated by the type and level of nutrient addition, and analyses of leaf N vs. P scaling relationships using pooled data could lose much information about biologically and ecologically significant variance. Overall, leaf N concentration scaled as 0.552 power of leaf P concentration for all data pooled. However, the scaling exponent decreased with increasing levels of N addition, but increased with increasing levels of P addition. This suggests that high availability of one nutrient decreases the variability of its own concentration, but promotes the fluctuation in concentration of another tightly associated nutrient in leaves among plant individuals. We call this the Nutrient Availability–Individual Variability Hypothesis. These findings have important implications for the parameterization of models of growth and nutrient cycles in terrestrial ecosystems, and for understanding population structures, processes and functioning under varying nutrient environments.