氮沉降增加和人类干扰对半干旱草地土壤呼吸的影响.

Soil respiration is the primary pathway for the global carbon cycle, but the response mechanism of soil respiration to global change and anthropogenic perturbation in semiarid grassland in the context of global change is still unclear. In this study, a field experiment was conducted to explore the effects of nitrogen (N) addition, anthropogenic perturbation, and their interactions on soil respiration throughout the growing season from May to September in 2017, in Horqin sandy land, northern China. In the field research, the nitrogen deposition included no nitrogen and nitrogen addition (10 g/(m²·a)), whereas, anthropogenic perturbation consisted of control, burning, and clipping activities. In soil respiration, the components and environmental factors, including soil temperature, soil moisture and soil microbial biomass carbon, were monitored in the whole plant growing season. The monitoring data was used to identify the effects of single factor, such as nitrogen deposition, burning and clipping, and their interaction on soil respiration, as well as the contributions of microbial and root respiration to soil respiration. The results showed that the soil respiration presented obvious seasonal dynamics, with the highest in July. Both soil temperature and soil moisture can regulate the seasonal variability pattern of soil respiration in the semiarid grassland, while nitrogen deposition, burning or clipping cannot alter that. The contribution ratios of microbial respiration to soil respiration were 64.68%, 54.99%, 69.20%, 57.88%, 50.50% and 57.66% under no nitrogen (N0)+control, N0+burning, N0+clipping, nitrogen addition (N10)+control, N10+burning and N10+clipping, respectively, indicating that the microbial respiration was main contributor to soil respiration in this semiarid grassland. The increased nitrogen deposition can remarkably enhance the root respiration by 42% (P<0.001), resulting in a significant increase in soil respiration by 17% (P<0.001). In the nitrogen addition, there was no significant effect on microbial respiration in this semiarid grassland, due to the nitrogen deposition cannot efficiently change soil microbial biomass. It infers that the decrease of soil carbon sequestration induced by nitrogen addition can mainly stem from the increase in the root respiration under the future global nitrogen deposition addition. The burning significantly increased the soil temperature, and thereby enhanced the root respiration by 25% (P<0.01), but it cannot efficiently increased the soil respiration, due to the reduction of microbial respiration that induced by the decrease of soil microbial biomass. Furthermore, the single nitrogen deposition enhanced the positive effect of single burning on soil respiration, indicating that both the nitrogen deposition and burning can be used to synergistically promote the soil respiration in this semiarid grassland. The clipping process significantly reduced the soil temperature by 7% (P<0.001), inducing the root respiration decreased by 20% (P<0.05). Moreover, the clipping significantly decreased the soil microbial biomass, and thus reduced the microbial respiration by 13% (P<0.001), thereby to effectively inhibit the soil respiration (16%, P<0.001). However, the nitrogen deposition and clipping had no significant interaction on the soil respiration. Different influences of nitrogen deposition, burning and clipping on soil respiration can provide the sound basis for the prediction of the soil carbon cycle, and for the scientific management of natural grassland in sandy grassland under the global climate change. [ABSTRACT FROM AUTHOR]