Effects of nitrogen deposition and plant litter alteration on soil respiration in a semiarid grassland.

Nitrogen (N) deposition and the input of litter to soils are expected to significantly affect soil respiration (Rs). However, the responses of Rs to N deposition and litter input alteration in semiarid grassland are still unclear. We investigated the effects of N addition, litter input alteration, and their interactions on Rs throughout the growing season from May to September in 2017, in Horqin grassland, Northern China. N deposition included N addition (10 g N m-2 year-1) and N control (0 g N m-2 year-1), and litter alteration consisting of litter removal, litter doubling and litter control were conducted. We found that N addition significantly improved vegetation coverage (P < 0.01) and thus increased root respiration (Rt) by 30% (P < 0.05), but did not significantly enhance Rs (P > 0.05) due to the negative effect of microbial respiration (Rm). Litter removal significantly decreased soil microbial biomass and thus reduced Rm (13%) and Rs (14%), but litter doubling did not significantly alter Rm, Rt and Rs. N addition slightly weakened the inhibition of litter removal and led to soil respiration was not significantly decreased, whereas N addition and litter doubling did not significantly interact with Rs. Furthermore, Rs and its components were mainly mediated by soil temperature, moisture, soil microbial biomass carbon (SMBC) and vegetation coverage, but the structural equation model found that soil temperature, SMBC and coverage were the key controlling factor of Rs, Rm and Rt, respectively. Different influences of N deposition and litter input on Rs, as well as the contributions of Rm and Rt to Rs identified could facilitate the evaluation and prediction of Rs and belowground C storage in grassland ecosystems in the context of future global changes.