The Carbon Storage Of Leymus Chinensis Grassland In The Songnen Plain Of Northeast China And The Responses Of Its Carbon Flux To Nitrogen Addition And Mowing

During the past three decades, carbon cycling has received unprecedented attention as an important function of terrestrial ecosystems. Grassland is the largest terrestrial biome on the earth, being utilized mainly by the means of mowing and grazing, and confronted with nitrogen deposition, which is one of the global change factors. However, there is no concensus yet concerning the effects of mowing and nitrogen deposition on carbon storage and carbon flux of grassland ecosystems. Leymus chinensis grassland on the Songnen Plain is an area sensitive to global climate change, and is fragile so as to be subject to human disturbance and global warming. During the two consecutive years of 2013 to 2014, we measured the carbon content in aboveground parts of plants, roots, litter and soil, and simultaneously monitored the gas exchange of the ecosystems. By so doing, we declared the status quo of carbon storage of Leymus chinensis grassland and the assessed the effects of mowing and nitrogen deposition on carbon flux of the Leymus chinensis grassland.The carbon storage of Leymus chinensis grassland in the Songnen plain was estimated as 321.1t/hm2、939.1 t/hm2 for the year 2013 and 2014 respectively. Due to the extraordinarily high precipitation and consequent flooding of 2013, the biomass and the carbon storage of 2014 was much larger than that in 2013. Using static chamber method, we observed and compared the changes of carbon flux of Leymus chinensis grassland ecosystem under mowing and simulated nitrogen deposition in Songnen plain, and found that Net Ecosystem Exchange, Total Ecosystem Respiration, and General Ecosystem Productivity under nitrogen addition are higher than the control, and those under mowing conditions are lower than the control. No difference was found in soil respiration among the treatments. During the whole growing season, the accumulated CO2 discharge of control, mowing and nitrogen addition treatments were estimated as 107.78 g·m-2·year-1,285.20 g·m-2·year-1 and 102.92 g·m-2·year-1, respectively. Therefore, we conclude that the investigated grassland ecosystem is carbon source, the strength of which was weakened by nitrogen addition, but strengthened by mowing of high frequency and intensity. It is inferred that the long-lasting fertilization may covert the grassland from carbon source to carbon sink. These findings implied that grassland ecosystem should be managed by rational grazing and proper fertilization, so that the function of production and of carbon sequestration, a most important ecological service, can be guaranteed at the same time, and thus sustainable use of grassland ecosystems can be realized.