Effect of Precipitation Variation on Soil Respiration in Rain-Fed Winter Wheat Systems on the Loess Plateau, China

Global climate change has aggravated the hydrological cycle by changing both the amount and distribution of precipitation, and this is especially notable in the semiarid Loess Plateau. How these precipitation variations have affected soil carbon (C) emission by the agroecosystems is still unclear. Here, to evaluate the effects of precipitation variation on soil respiration (R s ), a field experiment (from 2019 to 2020) was conducted with 3 levels of manipulation, including ambient precipitation (CK), 30% decreased precipitation (P −30 ), and 30% increased precipitation (P +30 ) in rain-fed winter wheat ( Triticum aestivum L.) agroecosystems on the Loess Plateau, China. The results showed that the average R s in P −30 treatment was significantly higher than those in the CK and P +30 treatments ( p < 0.05), and the cumulative CO 2 emissions were 406.37, 372.58 and 383.59 g C m −2 , respectively. Seasonal responses of R s to the soil volumetric moisture content (VWC) were affected by the different precipitation treatments. R s was quadratically correlated with the VWC in the CK and P +30 treatments, and the threshold of the optimal VWC for R s was approximately 16.06–17.07%. However, R s was a piecewise linear function of the VWC in the P −30 treatment. The synergism of soil temperature (T s ) and VWC can better explain the variation in soil respiration in the CK and P −30 treatments. However, an increase in precipitation led to the decoupling of the R s responses to T s . The temperature sensitivity of respiration (Q 10 ) varied with precipitation variation. Q 10 was positive correlated with seasonal T s in the CK and P +30 treatments, but exhibited a negative polynomial correlation with seasonal T s in the P −30 treatment. R s also exhibited diurnal clockwise hysteresis loops with T s in the three precipitation treatments, and the seasonal dynamics of the diurnal lag time were significantly negatively correlated with the VWC. Our study highlighted that understanding the synergistic and decoupled responses of R s and Q 10 to T s and VWC and the threshold of the change in response to the VWC under precipitation variation scenarios can benefit the prediction of future C balances in agroecosystems in semiarid regions under climate change.