Effects of soil fertility on the N:P stoichiometry of herbaceous plants on a nutrient-limited alpine steppe on the northern Tibetan Plateau

Abstract

Plant nutrient concentrations and their correlations with soil nutrient conditions are regarded as effective tools for exploring plant adaptation and resource utilisation strategies in a severe environment. However, few comparative studies have addressed the nutrient traits of different organs along natural fertility gradients. We quantified the nitrogen (N) and phosphorus (P) concentrations and N:P ratios in roots and leaves of 139 plant samples from 14 species on a nutrient-limited alpine steppe on the Tibetan Plateau. Next, we explored the correlation between root and leaf nutrient traits of different plant functional groups as well as soil fertility. Soil P had a significant impact on plant N:P stoichiometry, whereas soil N had little effect on plant nutrient traits. Leaf P and the N:P ratio of legumes exhibited more sensitive responses to soil P than roots. Among non-legume species, however, root N and P concentrations of Stipa purpurea and Orinus thoroldii (grasses) were more sensitive than N and P concentrations of leaves to variations in soil P availability. In contrast, leaf P and the N:P ratio of Leontopodium nanum, Potentilla bifurca and ect. (forbs) exhibited more sensitive responses to soil P than roots. Both root and leaf nutrient traits of Carex moorcroftii (sedges) were uncorrelated with soil fertility. The N:P stoichiometry of different functional groups showed disparate responses to soil P, and even the roots and leaves of the same functional group exhibited inconsistent correlations with soil nutrients. The distinct response patterns to soil nutrient conditions across functional groups helped elucidate the diversification of alpine plant adaptations to nutrient-poor environments and offered insights into quantifying the trade-off of different organs in co-existing species between resource use/conservation “strategies” and soil fertility.