Response of soil nitrogen pool to nitrogen and phosphorus addition in the wet meadow of the Qinghai-Tibet Plateau

Abstract

Abstract Background and aims The soil nitrogen (N) conversion process is an important part of the N cycle in wetland ecosystems, which regulates the content of soil available N and determines the retention status of soil N. N deposition and phosphorus (P) input caused by human activities will change the soil N pool, thereby affecting the soil function and conversion process. However, the responses of soil nitrogen pools to N and P addition in the QTP remain unknown. Methods In this study, an experiment was carried out for two years in wetlands situated on the Qinghai-Tibet Plateau. We analyzed the effects of N and P additions on soil nitrogen pool (i.e., blank control (CK), N addition (15 kg N ha− 1 yr− 1, N15), P addition (15 kg P ha− 1 yr− 1, P15), and NP co-addition (15 kg NP ha− 1 yr− 1, N15P15)), and discussed the main driving factors. Results The results showed that N and P addition significantly increased the contents of total nitrogen (TN) and ammonia nitrogen (NH4+-N) in 0-40cm soil layer, and decreased the contents of soil dissolved organic nitrogen (DON), but had no significant effect on the contents of soil microbial biomass nitrogen (MBN). The nitrate nitrogen (NO3−-N) content decreased under the N15 addition, and the TN storage was the highest under the P15 addition. Under each treatment, the surface soil (0-10cm) was more sensitive to N and P addition, while the deep soil was relatively stable. Redundancy analysis (RDA) showed that soil organic carbon (Explanation = 40.80%), soil density (Explanation = 8.70%), and carbon-to-nitrogen ratio (Explanation = 8.40%) were the main environmental factors affecting the content of each N fraction under the N and P addition. Conclusion N and P addition would affect the stability and transformation of wetland soil nitrogen pool, and the nitrogen transformation process was mainly regulated by soil physicochemical properties.