Carbon Storage Changes In Grassland Of Southern China Between1982to2012by Remote Sensing Process Model

Natural grasslands are one of the most widespread vegetation types worldwideand play a important role in the global carbon cycle. There are many studies aboutcarbon cycle of temperate grasslands in north China, however, the research onsouthern grasslands have been little studied. So, an improved understanding of thegrasslands in south China will be beneficial to developing a better understanding ofthe role these ecosystems play in regional carbon cycle. Based on the remote sensingdata, meteorological data and other related data from1982to2012, the grasslands insouth Chinawere analyzed by CASA (Carnegie-Ames-Stanford Approach) model.This study aims to fill the knowledge gap regarding the grasslands of south China andthe main conclusions are following:(1) With the1KM MODIS data and8KM AVHRR_PathFinder were used asmain remote sensing data input to CASA model, it showed that the overall level ofgrassland NPP in south China was beween300-450gC/m2. This value is obviouslyhigher than those in other grassland areas of China, which showed a strong ability ofcarbon sequestration.In these provinces in the study area, NPP is highest in Hainan,Jiangsu’s and Shanghai’s were relatively low, and the maximum accumulation ofcarbon is found in Yunnan because it has the most large grassland area.(2) There is significant positive relationship between field biomass data andNDVI vegetation index. The annual average carbon density of the grasslands of southChina was75.88gC/m2from1982to2012, and the above ground carbon stock isbetween14.7-23.12TgC. The multi-years average vale of the carbon stock for theunderground biomass was67.92TgC, ranged from51.14to80.29TgC, which is3.5times of oboveground carbon stocks.(3) There was a positive ralationship between soil baisc respiration value and soilorganic carbon value (R2=0.87，P<0.001), which shows the content of soilorganiccarbon directly decided the strength of soil respiration. The resutls show that theannual average value of soil organic carbon reseves was1.05PgC. Compared tovegetation carbon stocks, soil organic stocks of grasslands in south China was about12times that of vegetation pool. (4) During the31years, the southern grassland acted as a weak carbon source,with sealing37TgC into vegetation through photosynthesis, and releasing nearly40TgC by soil respiration. However, the carbon density of southern grassland in Chinawas obviously higher than that in the northern grassland, which showed it still havestrong ability to accumulate carbon.(5) A regression model was simulated with the independent factor of temperatureand precipitation. The results show that temperature is the main driving factor to NPPand the vegetation carbon stock accumulation (R2>0.7), and it has lower effect on thesoil carbon pool (R2=0.42). In the grasslands of the south China, precipitation wasnot a limiting factor for vegetation growth and thus higher temperatures may stimulategreater productivity with respect to vegetation.