PHYSIOLOGICAL ECOLOGY- ORIGINAL PAPER Stoichiometric homeostasis of vascular plants in the Inner Mongolia grassland

which an organism maintains its C:N:P ratios around a given species- or stage-specific value despite variation in the relative availabilities of elements in its resource sup-plies, is a key parameter in ecological stoichiometry. However, its regulation and role in affecting organismal and ecosystem processes is still poorly understood in vas-cular plants. We performed a sand culture experiment and a field nitrogen (N) and phosphorus (P) addition experiment to evaluate the strength of N, P and N:P homeostasis in higher plants in the Inner Mongolia grassland. Our results showed that homeostatic regulation coefficients (H) of vascular plants ranged from 1.93 to 14.5. H varied according to plant species, aboveground and belowground compartments, plant developmental stage, and overall plant nutrient content and N:P ratio. H for belowground and for foliage were inversely related, while H increased with plant developmental stage. H for N (HN) was consistently greater than H for P (HP) while H for N:P (HN:P) was consistently greater than HN and HP. Furthermore, species with greater N and P contents and lower N:P were less homeostatic, suggesting that more homeostatic plants are more conser-vative nutrient users. The results demonstrate that H of plants encompasses a considerable range but is stronger than that of algae and fungi and weaker than that of ani-mals. This is the first comprehensive evaluation of factors influencing stoichiometric homeostasis in vascular plants