Responses of Ecosystem's Carbon and Water Fluxes to Global Change on the Songnen Steppe

The global warming and a changing nitrogen regime could have a profound impact on ecosystem's carbon flux,therefore,a good understanding of carbon flux responses to changing environmental conditions is critical for predicting the productivity and carbon sequestration potential of grass ecosystems during the 21st century. Measurements of photosynthetic characteristics were made in Yangcao (Leymus chinensis) grassland under a warming and nitrogen deposition soil during the period from 2006 to 2009. In situ diurnal Net Ecosystem CO2 Exchange (NEE) was measured by determining the rise in CO2 in IRGA. Analysis of CO2 fluxes during 4 years shows that the climate warming reduces NEE,Gross Ecosystem Productivity (GEP) and Evapotranspiration (ET),while increases Ecosystem Respiration (ER) and ecosystem Water-Use Efficiency (WUE). The increased N stimulates the NEE,ER,GEP and WUE. Under conditions of warming plus nitrogen,the nitrogen ameliorates the negative impacts of climatic warming on ecosystem carbon fluxes. Carbon flux responses to global change were driven overwhelmingly by gains and losses by Leymus chinensis,as the native plants in the Songnen grassland. Climate change could rapidly alter carbon fluxes in the Songnen grassland. These results provide an understanding of the future impact of the terrestrial carbon-cycle feedback on the global climate change.