Differential response to warming of the uptake of nitrogen by plant species in non-degraded and degraded alpine grasslands

Purpose Chemical niche differentiation and changes in the dominance of plant species have been proposed as mechanisms for the coexistence of different types of plants. We explored how dominant plant species take up ammonium (NH4+), nitrate (NO3-), and glycine under conditions of warming and soil degradation in alpine grasslands. Materials and methods Open-top chambers were used to simulate warming in degraded and non-degraded plots in an alpine grassland ecosystem on the Tibetan Plateau. Plant species were selected in both non-degraded (Kobresia pygmaea and Aster tataricus) and degraded (Aster tataricus and Chenopodium glaucum) plots. Short-term N-15-labeling experiments with NH4+-N, NO3--N, and glycine ((CN)-C-13-N-15-glycine) were conducted in each of four subplots with water alone as the control. Results and discussion All of the selected plant species took up both organic and inorganic forms of N in the K. pygmaea grassland. Warming increased the uptake of glycine-N by the dominant species, whereas the uptake of NH4+-N by the non-dominant species increased in both non-degraded and degraded grasslands. Warming changed the N uptake preference of A. tataricus from NO3--N to NH4+-N in non-degraded grasslands, but did not change the preference of A. tataricus under degraded conditions. This suggests that degradation can affect the preference of different plant species for particular forms of N as a response to warming. Conclusions Plants in K. pygmaea grasslands take up organic N, although inorganic N is the dominant form of N used. The effects of warming on the uptake of N by plants varied with species, the form of N, and the degradation of the grassland. Degradation modified the effect of warming on the preference of plants for different forms of N. Different plant species developed different patterns for the uptake of N in both non-degraded and degraded plots, which may facilitate their coexistence in alpine grasslands.