Changes in Soil Nutrient Storage and Their Controlling Variables Under Different Treatments Across Northern China’s Meadow Grassland

Meadow grasslands are characterized by high primary productivity and are an important ecological barrier against sandstorms and desertification in northern China. The dynamic changes in reserves of soil organic carbon stocks (SOCSs), total nitrogen (TNS), and total phosphorus (TPS) in grassland ecosystems are easily disturbed by human activities. However, the effects of different treatments on the relationships among soil nutrient reserves (SOCS, TNS, and TPS) and the mechanisms underlying the effects of various key variables on changes in soil nutrient reserves remain unclear. This study investigated the changes in soil nutrient reserves in meadow grasslands in northern China after mowing (M), burning (F), and grazing (G) treatments than without any anthropogenic interference (E, control) from 2020 to 2023, as well as the vegetation and soil variables that may affect them. The results showed that compared with the control treatment, once-a-year mowing and burning significantly increased SOCS (M: 12.75%, F: 23.72%), TNS (M: 15.6%, F: 26.8%), TPS (12.4%, 27.2%) and strengthened the correlations between SOCS and TNS and between SOCS and TPS, while grazing treatments significantly reduced soil nutrient reserves (13.0%, 11.8%, 10.1%) and the correlation between soil nutrient reserves. In general, under different treatments, soil temperature was the important control variable affecting each reserve. Vegetation was also a key control variable affecting SOCS, while TNS and TPS were mainly regulated by soil factors. It should be pointed out that owing to different treatments, the key vegetation variables affecting SOCS differed notably from those affecting TNS and TPS. This study emphasized the impact of different treatments on soil nutrient reserves and their main controlling variables, providing an important theoretical basis for further optimizing and improving the scientific management strategy of grassland ecosystems.