Tibetan sheep grazing and selenium addition promote soil carbon and nitrogen mineralization in alpine meadow

Grazing has been confirmed to alter the carbon (C) and nitrogen (N) cycling of alpine meadow ecosystems by improving soil C and N mineralization. However, research on how selenium (Se) addition and its interaction with grazing affected vegetation traits and soil properties, and how they related to soil C and N mineralization remained inadequate in the Qinghai-Tibetan Plateau (QTP) alpine meadow, which is one of the regions soil Se deficient worldwide. We quantified vegetation traits, soil physical properties, soil nutrient density, and nutrient stoichiometry, as well as investigated soil C and N mineralization change in two-year field experiments conducted in an alpine meadow, using a split-plot design with grazing as the main-plot factor and Se addition as the split-plot factor. The results showed that soil C and N mineralization were significantly affected by Se addition, and grazing significantly impacted C mineralization. Se addition significantly affected soil physical properties but grazing had not. For soil nutrient density, grazing had no significant impact on soil organic carbon density (SOCD), while significantly decreasing soil available nitrogen density (SAND) and the soil available nitrogen density to soil total nitrogen density ratio (SAND/STND), and increasing soil available phosphorus density (SAPD) and soil total phosphorus density (STPD). Se addition significantly affected SOCD, SAND, and SAND/ STND. Grazing and Se addition alteration of soil C and N mineralization were closely linked to the changes in vegetation traits and soil physical properties. The random forest model further revealed vegetation traits and soil physical properties were important predictors of soil C and N mineralization. This study provided valuable information for moderate grazing and suitable Se addition to maintain soil nutrient availability and the sustainability of the alpine meadow ecosystems in the QTP even worldwide.