The community-level scaling relationship between leaf nitrogen and phosphorus changes with plant growth, climate and nutrient limitation

The scaling relationship between the concentrations of leaf nitrogen (N) and phosphorus (P), which can be formulated as [N] = alpha[P](beta), shows the relative investment of plants in nutrient uptake. Most of the current knowledge on this topic is based on studies at the individual or species level. However, patterns at these levels can hardly reflect the response of vegetation or ecosystems along environmental gradients. Here, we explored how the nutrient demands of vegetation as a whole vary with productivity, climate and soil nutrient availability by generalizing the scaling relationship from the individual to the community level using community-weighted mean data from shrub communities at 1,080 shrubland sites and tree communities at 2,087 forest sites across China. By comparing the community-level leaf N-P scaling exponents under different conditions and using a bootstrapping method to construct continuous environmental gradients, we found that the scaling exponents declined with increased primary productivity (i.e. growth rate at the community level), temperature and water availability, indicating a higher P demand relative to N under these conditions. In addition, the scaling exponent of shrub communities had a declining trend, while that of tree communities had a rising trend, with higher soil N availability, showing a more resistant response of shrub communities to nutrient limitation. Synthesis. Our study demonstrates that leaf N-P scaling exponents could be used as indicators of plant growth conditions and, more importantly, that communities, as assemblages of plants, exhibits varied nutrient preferences and utilization strategies among different habitat conditions.