The regulatory effects of biotic and abiotic factors on soil respiration under different land-use types

Abstract Assessing the impacts of land use on soil respiration (Rs) and its temperature sensitivity (Q10) is of vital significance for understanding regional carbon cycles. In this study, the regulation of Rs and Q10 by soil biotic and abiotic factors under different land-use types, i.e., cropland, apple orchard, abandoned land, Coronilla varia grassland, and Robinia pseudoacacia woodland, were examined in the Luoyugou watershed on the Chinese Loess Plateau. We monitored Rs, soil temperature, and moisture in situ from July to December 2018 and evaluated soil microbial abundance, root biomass, carbon and nitrogen nutrient levels. The results showed that soil organic carbon, total nitrogen, available nitrogen, dissolved organic carbon, and microbial biomass carbon decreased by the following order: grassland > woodland > abandoned land > cropland > orchard. The high amounts of plant residues and the low levels of human disturbance in grassland and woodland contributed to higher soil carbon and nitrogen nutrient levels in these land-use types than in cropland and orchard. Rs decreased from July to December, with soil temperature and moisture being the key explanatory factors. The mean Rs in grassland (3.68 μmol m−2 s−1) and woodland (3.81 μmol m−2 s−1) was significantly higher than that in cropland, orchard, and abandoned land. Q10 ranged from 1.77 to 5.87 across all land-use types, and orchard, abandoned land, grassland, and woodland had Q10 values 1.91, 1.37, 1.47, and 3.32 times higher, respectively, than the Q10 of cropland. The variable importance in the projection (VIP) values from the partial least squares regression model showed that soil temperature (VIP = 1.41), pH (VIP = 1.22), microbial biomass nitrogen (VIP = 1.13), microbial biomass carbon (VIP = 1.12), bacterial abundance (VIP = 1.12), available nitrogen (VIP = 1.01), and soil moisture (VIP = 1.01) were the most important predictors of Rs. Our study suggests that soil temperature and labile organic matter exert stronger impacts on Rs than do microbial abundance and root biomass. Our results contribute to a better understanding of ecosystem carbon cycles.