Nitrogen enrichment enhances the competition for nitrogen uptake between Stipa purpurea and microorganisms in a tibetan alpine steppe.

Aims: Numerous studies have investigated whether plant growth is limited by the availability of nitrogen or phosphorus (or both) in alpine grasslands. However, few studies have assessed N and P limitations on plant growth by comparing plant-microbial competition for N. Methods: An in situ 15N labeling experiment using NO3−, NH4+, and glycine was carried out with N and P additions in an alpine steppe on the Qinghai-Tibetan Plateau. Results: Plant biomass production in the alpine steppe was limited by N but not by P. Notably, N uptake of microorganisms and the dominant plant species, Stipa purpurea was greatly improved by N addition. Furthermore, the uptake of NH4+ by S. purpurea and other plants increased with P addition. The addition of N and P together promoted the uptake of NO3− by microorganisms. Alleviating N limitation (i.e., N or NP fertilization) resulted in a higher uptake of N by microorganisms than that by S. purpurea. Conclusion: Nitrogen enrichment promoted the dominant competitive role of microorganisms over plants in terms of N uptake in the short term. This study provides a comprehensive basis for plant N uptake during the process of alleviating nutrient limitation in alpine grasslands by comparing short-term plant-microbial competition. [ABSTRACT FROM AUTHOR]