Nitrogen and phosphorus supply controls stability of soil organic carbon in alpine meadow of the Qinghai-Tibetan Plateau

Abstract

Anthropogenic activities have significantly increased soil nutrient availability, thereby influencing ecosystem processes and functions, particularly in nutrient-limited ecosystems like alpine grasslands. Despite substantial efforts dedicated to comprehending the responses of plant productivity and community composition to nitrogen (N) and phosphorus (P) addition, our understanding of the effects of nutrient additions on soil organic carbon (SOC) remains limited. Here, we implemented a 12-year manipulative fertilization study with three levels (0, 10 and 30 g m^‐2) of N, P, and NP fertilization (N and P fertilization at a ratio of 1:1) in an alpine meadow of the Qinghai-Tibetan Plateau. Results showed that N and P additions increased the content of soil organic carbon compared with control. Under the same fertilization conditions, soil organic carbon content increased with the increases of fertilization level, and reached the maximum under N30 treatment (P < 0.05). N and P additions promote the labile carbon (polysaccharide-C and alcohol-C) consumption and the stable carbon (aromatic C and aliphatic-C) enrichment, consequently, it improved the stability of soil organic carbon and facilitated the sequestration of soil organic carbon in alpine meadow. The highest stability of soil organic carbon presented in NP30 treatment compared with others treatments. Indicating that NP addition simultaneously can promote the stability of SOC more. The structural equation modeling (SEM) revealed that under the N and P additions treatments, the main factors affecting soil organic carbon stability were soil organic carbon, pH, ratio of carbon and phosphorus (C:P), ratio of carbon and nitrogen (C:N), soil available N:P (AN: AP), available phosphorus (AP), soil available C:N (AC:AN), soil water content (SWC), total nitrogen (TN), available (AN). Overall, nitrogen and phosphorus additions altered soil physicochemical properties as well as the composition of functional groups within soil organic carbon in alpine grasslands, ultimately promoting its accumulation while also impacting both the content and stability of soil organic carbon.