Responses of soil respiration to N addition, burning and clipping in temperate semiarid grassland in northern China

Soil respiration is an important part of the global carbon (C) cycle and the largest component of C flux from terrestrial ecosystems to the atmosphere. Global change and anthropogenic perturbations can profoundly impact soil respiration. A field experiment examined the seasonal variability of soil respiration in response to the addition of nitrogen (N), burning, clipping and their possible interactions throughout an entire growing season from April to October 2011, in semiarid grassland in northern China. Results showed that N addition and burning significantly increased mean soil respiration by 35.8% and 11.0%, respectively, and that burning and N addition synergistically enhanced soil respiration. However, the effects of N addition and burning on soil respiration were mediated by season. Clipping had no significant effect on soil respiration. Soil moisture was primarily responsible for the seasonal changes in soil respiration, whereas the positive responses of soil respiration to burning and N addition were attributable to elevated soil temperature, plant growth, root and microbial activity and respiration. In unfertilized plots, burning decreased temperature sensitivity (Q10) of soil respiration by 10.0%. In plots with N addition, burning and clipping decreased Q10 by 15.4% and 11.6%, respectively. We therefore conclude that burning can, and clipping may, decrease the dependence of soil respiration on temperature. We further observed that the magnitude of positive feedback in soil respiration to temperature increase weakened in the burned plots, and that the availability of N might regulate the degree of this weakening. The different mechanisms by which N addition, burning and clipping influence soil respiration and its sensitivity to temperature identified in this study may facilitate the simulation and prediction of C cycling in semiarid grassland under future scenarios of global change.