[Effects of Simulated Precipitation Reduction on Soil Respiration in a Soybean-Winter Wheat Rotation Cropland]

To investigate the effects of precipitation reduction on soil respiration in rainfed croplands, a field experiment was performed in a soybean-winter wheat cropland. A randomized block design including three treatments, viz. control (CK), 20% precipitation reduction (P20%), and 40% precipitation reduction (P40%), was used. Seasonal variabilities in soil respiration, soil temperature, and soil moisture were measured. Rates of soil CO₂ production, nitrification and denitrification, and harvested crop biomass were also measured. Results indicated that the seasonal mean soil respiration rates for CK, P20%, and P40% treatments in the soybean growing season were (4.91±0.67), (4.19±0.39), and (4.35±0.32) μmol·(m²·s)^-1, respectively. There was no significant difference (P>0.05) in the mean soil respiration rates between treatments during the soybean growing season. The seasonal mean soil respiration rates for CK, P20%, and P40% treatments during the winter wheat growing season were (2.39±0.17), (2.03±0.02), and (1.94±0.05) μmol·(m²·s)^-1, respectively. There was a significant (P<0.05) difference in the mean soil respiration rates between treatments during the winter wheat growing season. Precipitation reduction decreased the soil CO₂ production rates, but had no obvious impacts on soil nitrification and denitrification rates. Precipitation reduction had no significant (P>0.05) effects on the root, shoot, and seed biomass of soybean, but significantly (P<0.05) decreased the root, shoot, and seed biomass of winter wheat. Soil temperature was the main driver of the seasonal variation in soil respiration. Soil respiration increased exponentially with the increase in soil temperature. There was no significant (P>0.05) difference in the coefficient of temperature sensitivity (Q₁₀) between different treatments. Based on the precipitation reduction experiments of duration longer than one year in previous studies and in our present study, a significant linear regression relationship between the amount of reduced soil respiration and the amount of precipitation reduction was found, indicating that substantial precipitation reduction showed more obvious inhibition effects on soil respiration. This study also suggested that the effects of precipitation reduction on soil respiration varied between crop growing seasons, which may be attributed to the different precipitation intensities in different growing seasons.