| The global climate change including warming and the variation of precipitation is the major problems which influence sustainable development of economy and environment. Carbon-water cycle is the key processes of material cycle and energy flow in the terrestrial ecosystem, which is the important link of pedosphere-biosphere-atmosphere interaction. With the global climate change, using59years of meteorological data of Qian-guo county, CO2flux and micro-meteorological data (2008-2010) from a eddy tower setted in Songnen meadow steppe, The precipitation patterns change and its impact on carbon flux were investigated. The main results were as the following:(1) The sum of the mean precipitation frequency, the mean precipitation by times and the daily mean precipitation were17.84n,17.11mm and3.23mm, respectively in the growing season (June, July and August) from1953to2011. These values were higher than that in the northwest region and the typical Inner Mongolia grassland, which might be the reason for the larger carbon sink since2007in Songnen grassland and carbon sink was significantly higher than Inner Mongolia grassland ecosystems. Precipitation and precipitation frequency had obvious seasonal variation. The precipitation frequency, the mean precipitation by times and the daily mean precipitation reached the highest in the growing season and the precipitation frequency and the daily mean precipitation in August were higher than in June. The rainfall times in growing season had little change and the mean precipitation by times and the daily mean precipitation showed a decline trend in the past60years, which increased the possibility of drought in the region.(2) From1953to2011, the annul precipitation and the precipitation in the growing season presented declining trend and the latter was more obvious. The days of annual precipitation and the little rain showed a more significant increase trend, but the days of precipitation, moderate rain and heavy rain all decreased. The contribution of different intensity precipitations to days of precipitation changed significantly. In growing season the precipitation days and little rain days represented little decrease trend. Compared with the annual rainfall, the middle rainfall and the heavy rainfall showed distinctly decline tendency. We found the storm only occur in June, July and August.(3) Micro-meteorological factors varied in the growing season. The highest soil water potential (SWP) presented in July, which was much higher than that in June and August. The temperature at one day before rainfall was significantly higher (P<0.05) than that at one day after rainfall in growing season. As the precipitation occurred, SWP showed different variation in growing season (June, July and August). The SWP values of three days after rainfall were higher than that of three days before rainfall in July, but after rainfall the values of SWP declined in June and August. These factors directly affected the variation of net ecosystem CO2exchange (NEE). The NEE in July was the largest, showing a strong carbon sink and was the biggest contribution to the annual NEE.(4) In Songnen grassland ecosystem, precipitation patterns not only determined the direction of the water flow, but also the ability of ecosystems to absorb carbon. As precipitation increased, air vapor pressure would increase, which increased water infiltration into the soil, so the precipitation had a positive correlation with SVP (saturation vapor pressure) and SWP. With increasing precipitation, SVP value increased, the biggest value was nearly4kPa in growing season, and NEE showed a significant increase. When SVP was at the same level and temperature was different, NEE appeared significant difference:When temperature was above25℃and SVP was lower than3kpa, NEE were less than that when temperature was below25℃. Under the same temperature conditions (T<25℃), NEE showed a rising trend. with SVP increasing, and the NEE (SVP>3kpa) was larger than that(SVP<1kpa),and significant difference was observed (P<0.05). |
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