Response of carbon dioxide emissions to sheep grazing and N application in an alpine grassland – Part 2: Effect of N application

摘要

Widespread nitrogen (N) enrichment resulting from anthropogenic activitieshas led to great changes in carbon exchange between the terrestrial biosphereand the atmosphere. Grassland is one of the most sensitive ecosystems to Ndeposition. However, the effect of N deposition on ecosystem respiration(R_e) in grasslands has been conducted mainly in temperategrasslands, which are limited largely by water availability, with few studiesfocused on alpine grasslands that are primarily constrained by lowtemperatures. Failure to assess the magnitude of the response inR_e outside the growing season (NGS) in previous studies alsolimits our understanding of carbon exchange under N deposition conditions. Toaddress these knowledge gaps we used a combination of static closed chambersand gas chromatography in an alpine grassland from 2010 to 2011 to test theeffects of N application on ecosystem respiration (R_e) bothinside and outside the growing season. There was no significant change inCO₂ emissions under N application. R_e outside the growingseason was at least equivalent to 9.4% of the CO₂ fluxes during thegrowing season (GS). Annual R_e was calculated to be279.0–403.9 g CO₂ m?2 yr?1 in Bayinbuluk alpinegrasslands. In addition, our results indicate that soil temperature was thedominant abiotic factor regulating variation in R_e in the cold and aridenvironment. Our results suggest that short-term N additions exert nosignificant effect on CO₂ emissions in alpine grassland.