The Response Of Carbon Dioxide Exchange To Pricipitation Change In Yunwu Moutain Typical Grassland

Carbon cycle plays a key role in the structure, production and function of grassland ecosystem. The process of CO2 exchange in grassland ecosystem will change greatly under the background of spatial and temporal change of precipitation, and it will impact the feedback between ecosystem and climate system. A field manipulative rainfall control experiment was conducted to measure the response of the CO2 exchange process(photosynthesis, respiration and soil respiration) to annual and seasonal precipitation change as well as environmental factor(soil moisture and temperature) in arid and semi-arid grassland ecosystem. The main research results were as follows:1. The biomass of grassland increased with increasing precipitation. The biomass of during 2013 and 2014 two growing seasons were ranked in the order of rainy year>normal precipitation>drought year. The biomass of grassland after clipping in 2013 were ranked in the order of normal precipitation>drought year>rainy year. For clipping grassland the relationship between biomass and precipitation was different in 2013 and 2014.In 2013 the biomass of grassland were in the order of normal precipitation>drought year>rainy year but the maximal biomass of grassland was under the drought year treatment in 2014.It shows that long fenncing time and natural succession of grassland community was limited by moisture, which could be relived by clipping.2. The soil respiration of grassland ecosystem had significant daily and seasonal variation in Yunwu Mountain. Two growing season daily variation of soil respiration showed a single-peak curve model, and the maximum value appeared between 13:00 to 15:00.The average daily respiration rate of grassland after clipping in 2014 were ranked in the order of rainy year>normal precipitation>drought year. The seasonal variation of soil respiration was in the order of summer > autumn > spring > winter. The annual average value of soil respiration increased 0.57umol/(m2?s) by mowing measures,which increased carbon emissions. The correlation between soil temperature and soil respiration was well fitted by exponential equation, and the temperature sensitivity coefficient was between 2.5 to 4.0.3. The respiration rate of grassland ecosystem had significant daily and seasonal variation. The highest respiration appeared between12:00and 14:00 every day. The average respiration rate of the non-clipping grassland was higher than that of clipping grassland under the same precipitation treatment. The average daily respiration rate of grassland after clipping in 2013 were ranked in the order of rainy year>normal precipitation>drought year, but in 2014 the order of ecosystem respiration was normal precipitation>rainy year>drought year. Therefore the treatment of drought year decreased the respiration rate of grassland ecosystem but rainy year showed different patterns in the two growing seasons. The variation trend of ecosystem respiration in growing season was very obvious single-peak curve in 2014. The ecosystem respiration of the clipping grassland and non-clipping grassland treatment were11.23umol/(m2?s) and 10.15umol/(m2?s) respectively. The temperature sensitivity coefficient of ecosystem was between 2.21 and 3.39.4. The net gas exchange of community was part of the net carbon fixation of ecosystem, and it was affected by many variations on time scale. The maximum net gas exchange capacity appeared between 10:00 and 12:00. The net gas exchange capacity of grassland after clipping in 2013 and 2014 were ranked in the order of drought year>rainy year>normal precipitation and rainy year>normal precipitation>drought year respectively. The net gas exchange capacity was greatly affected by growing season and climate variables, and the diurnal variation was significant change. The seasonal change of net gas exchange capacity was obvious, and the maximum value appeared in July. The net gas exchange capacity in non-clipping and clipping grassland were 7.2umol/(m2?s) and 6.6umol/(m2?s) respectively.