Regulation mechanism of δ15N in alpine meadow plants and soil of Qinghai-Tibet Plateau under nitrogen addition

Abstractδ15N values in plants and soils can effectively help understand nitrogen cycling in ecosystems, however the driving factors and mechanisms of nitrogen cycling in alpine meadow ecosystems of the Three-River Source region are largely unknown, especially under different nitrogen form additions. To address this knowledge gap, we conducted a15N tracer field micro-plot experiment from June 2020 to September 2022 at an alpine meadow site in Qinghai Province, China, with three nitrogen forms added ((15NH4)2SO4, Ca(15NO3)2, and CO(15NH2)2) to calculate corresponding δ15Nplant and δ15Nsoil values. The results showed that (1) under different nitrogen form additions, δ15Nplant, δ15Nsoil, soil and vegetation properties all exhibited significant differences, with CO(15NH2)2addition resulting in markedly higher δ15Nplant, δ15Nsoil, total soil N, plant total N, and plant biomass compared to (15NH4)2SO4and Ca(15NO3)2treatments, while Shannon-Wiener diversity and Margalef richness indices reached maximum values under Ca(15NO3)2addition. (2) The most influential variables for δ15Nplant and δ15Nsoil were Shannon-Wiener index and mean annual temperature under (15NH4)2SO4addition, plant biomass and plant total N under Ca(15NO3)2addition, and plant total N and mean annual temperature under CO(15NH2)2addition. Overall, this study highlights the complexity of climate, soil and plant factors influencing δ15Nplant and δ15Nsoil under different nitrogen form additions, providing a theoretical basis for the mechanisms of δ15Nplant and δ15Nsoil variation in alpine meadow ecosystems of the Three-River Source region.