Response of carbon dioxide emissions to sheep grazing and N application in an alpine grassland – Part 1: Effect of sheep grazing

Abstract. Previous work has failed to address fully the response of (autotrophic and heterotrophic) respiration to grazing in different ecosystems, particularly in alpine grasslands outside the growing season. From 2010 to 2011 a field experiment combined two methods (static closed chambers and a closed dynamic soil CO₂ flux system) in alpine grasslands located in the Tianshan Mountains. We examined the effects of grazing regime on ecosystem respiration (R_e) both outside (NGS) and during (GS) the growing season and determined the pattern of R_e in relation to climate change. There was no significant change in CO₂ emissions under grazing. Heterotrophic respiration (R_h) accounted for 78.5% of R_e with short-term grazing exclusion and 93.2% of R_e with long-term grazing exclusion. R_e, R_h and autotrophic respiration (R_a) fluxes outside the growing season were equivalent to 12.9%, 14.1% and 11.4% of the respective CO₂ fluxes during the growing season. In addition, our results indicate that soil water content played a critical role in R_a in the cold and arid environment. Both R_h and R_e were sensitive to soil temperature. Moreover, our results suggest that grazing exerted no significant effect on CO₂ emissions in these alpine grasslands.