[Stoichiometric Imbalance of Abandoned Grassland Under Precipitation Changes Regulate Soil Respiration]

As a key factor of global climate change, precipitation can affect soil respiration. Microorganisms are the key drivers of soil respiration, but the relationship between microbial stoichiometry and respiration in vulnerable habitat areas under different precipitation gradients is unclear. In this study, five precipitation gradients were simulated on a typical abandoned grassland in the loess hilly region. Soil respiration, nutrients, microbial biomass, and extracellular enzymes were measured, and the microbial measurement characteristics were calculated. The results showed that:①soil respiration (SR) increased significantly under rainfed treatment but decreased significantly under D50 treatment. ②Precipitation changes affected the stoichiometric imbalance, and the N:P imbalance of the active resource pool presented a u-shaped trend, whereas the C:P imbalance changed significantly only in 2019, with a trend of P50>P25>CK>D25>D50. Additionally, the stoichiometric imbalance was caused by the soil stoichiometry. In 2019, the C:P imbalance of the active resource pool showed a trend of P50>P25>CK>D25>D50, whereas the N:P imbalance of the active resource pool showed a u-shaped trend, and the stoichiometric imbalance was caused by soil stoichiometry changes. ③Soil β-1,4-glucosidase (BG) enzyme decreased with increasing precipitation, and the sum activities of β-1,4-N-acetylglucosaminidase (NAG) and leucine aminopeptidase (LAP) significantly decreased during two years of rainfall reduction treatment. The activity of alkaline phosphatase (ALP) significantly increased under increasing rainfall but significantly decreased under decreasing rainfall. BG:(NAG+LAP) and BG:ALP were significantly decreased under increasing precipitation conditions but significantly increased under decreasing precipitation conditions. ④The partial least squares path model (PLS-PM) showed that precipitation had an impact on soil respiration through influencing C:P stoichiometric imbalance and soil enzyme stoichiometric ratio. These results highlight the importance of stoichiometric imbalances in regulating soil respiration and may help predict how they are caused by precipitation change control carbon cycling and nutrient flow in terrestrial ecosystems.