Effects of warming and precipitation changes on soil organic carbon and enzyme activities in semi-arid wheatland fields on the Loess Plateau of central Gansu Province, China.

Farmland ecosystems are strongly affected by climate change, but the effects of global warming and precipitation changes and their interactions on soil organic carbon and enzyme activities in farmland soils and their relationships are still poorly understood. In this study, we employed the Open-Top Chamber (OTC) warming platform and the precipitation manipulative platform to investigate the effects of warming and precipitation changes on soil organic carbon and enzyme activities in semi-arid spring wheat farmland in Loess Plateau of the central Gansu Pro-vince. There were six treatments: control (CK), 30% precipitation reduction (-P₃₀), 30% precipitation increase (+P₃₀), warming (W), warming and 30% precipitation reduction (W-P₃₀), and warming and 30% precipitation increase (W+P₃₀). The results showed that OTC warming significantly elevated soil organic carbon (SOC), microbial biomass carbon (MBC), readily oxidizable organic carbon (KMnO₄-C), dissolved organic carbon (DOC), and particulate organic carbon (POC) contents. In contrast, the mineral associated organic carbon (MAOC) content changed little. Under ambient temperature, neither an increase nor a decrease in precipitation resulted in a significant alteration of soil organic carbon fractions. However, under the warming condition, elevated precipitation resulted in a notable enhancement in DOC and POC contents. Warming and precipitation significantly interacted to affect SOC, DOC, and KMnO₄-C contents. The interaction between precipitation and warming resulted in an increase in the carbon pool management index (CMI), the carbon pool index (CPI), the activity of soil cellobiose hydrolase, urease, sucrase, N-acetyl-β-D-glucosidase, as well as crop biomass. The correlations between soil temperature, moisture, soil organic carbon fractions and enzyme activities were positive. There was a negative correlation between soil temperature and sucrase activity. The random forest modelling analysis demonstrated that soil physicochemical properties, enzyme activities, temperature and water content together explained 52.4% to 71.1%, and the five factors with higher correlation importance were soil urease activity, soil temperature, soil moisture, soil N-acetyl-β-D-glucosidase activity, and effective phosphorus. However, the selected factors only accounted for 21.5% of the observed variation in MAOC content. In conclusion, warming and precipitation changes significantly affected soil properties, enzyme activities and crop biomass, and thus soil organic carbon pools, in semi-arid wheatland soil of Loess Plateau of central Gansu Province.