Effects of nitrogen and phosphorus addition on the mineralization potential of soil organic carbon and the corresponding regulations in the Tibetan alpine grassland

As a crucial property for assessing the stability of soil organic carbon (SOC), the mineralization potential of SOC (RSOC) is often considered vital for soil carbon (C) dynamics. Previous studies have investigated the responses of RSOC and the corresponding regulation of increased nitrogen (N) and phosphorus (P) inputs, among which, the response of RSOC would affect SOC accumulation directly, emphasizing the significance of investigating RSOC. Hence, based on a long-term nutrient addition experiment in a Tibetan alpine grassland, this study assessed RSOC using a 45-day soil incubation experiment with 13C-glucose labeling method and explored the underlying mechanisms. The results demonstrated bacterial richness and diversity decreased in the topsoil due to the lower pH caused by the continuous N addition, whereas fungal richness and diversity had no significant change. And RSOC decreased with N addition in the topsoil because of suppressing the physiological process of microbes for N. Our results highlighted the crucial role of C availability (indicated by dissolved organic carbon) and N availability (indicated by total nitrogen) in controlling RSOC with long-term nutrient addition in the top- and subsoil, respectively. Overall, this study elucidated the impact of N and P addition on RSOC and offered the regulatory mechanisms of RSOC by considering soil, plant and microbial properties. These findings can serve as a basis for anticipating the changes in SOC dynamics in response to enhanced N and P deposition.