Variations of nitrogen and phosphorus between leaf, stem and root in shrubland biomes and responses to climate and soil factors across the Hengduan Mountains, China

The allocations of nitrogen (N) and phosphorus (P) among plant organs reflect plants' response and adaptation mechanisms to the environment. However, previous studies on plants' N and P stoichiometric characteristics have mainly focused on leaves, with little known about nutrient associations between organs and whether these are influenced by plant type and environment. We explored the allocation strategies of N and P between plant organs and their responses to changes in climate and soil. We analyzed 495 shrub organ samples from 112 shrub biomes at altitudes ranging from 942 to 4685 m. In this study, N and P concentrations were higher and more stable in leaves than in stems and roots, and scaling relationships of N or P concentrations among organs tended to be allometric. As shrubs' nutrients increased, shrubs at low altitudes presented a faster increase in non-leaf organ nutrients, while shrubs at high altitudes showed a faster increase in leaf nutrients. As mean annual temperature and mean annual precipitation increased, P concentrations decreased in leaves and increased in non-leaf organs. We found no significant correlations between organs' N concentrations and soil N concentrations, but there were significant positive correlations after excluding Legume shrubs. Further analyses showed that variations of N concentrations in all organs were explained mainly by shrub type and relatively less by soil nutrients and climate. Variation of leaf P concentrations was explained mainly by shrub type, but variations of non-leaf organ P concentrations were explained primarily by climate and soil nutrients. Across an extensive altitudinal gradient, we found the pattern of the response of nutrient accumulation in shrub organs to environmental changes, which deepened our understanding of nutrient allocation strategies of plant and their potential responses to global climate changes in the plateau ecosystem.