Research On The Temporal-spatial Differences Of Carbon Sources And Sinks Of Farmland Ecosystems And The Techniques To Sequester Carbon

With the aggravation of Global warming effect, in order to search for appropriate strategies to decrease the concentration of GHGs (Greenhouse Gases) in the atmosphere, research on carbon cycle and carbon budget of terrestrial ecosystems has been a hot topic in the field of global change. Farmland ecosystem is not only a man-made type of terrestrial ecosystem, but also important sources and sinks of GHGs. Farmland ecosystems, on the one hand, absorb a great deal of carbon through photosynthesis and anthropogenic impacts, on the other hand, give out GHGs through agricultural producing processes and respiration of crops and soil. Furthermore, the transformation of land from natural state to cropland also leads to the loss of SOC (Soil Organic Carbon). With the increasing of farming intensity, agricultural sector faces more and more carbon emission. Accordingly, how to increase carbon sequestration in farmland soil through adopting suitable strategies has been one of the most urgent problems in this field.Firstly, this dissertation estimated the size of carbon source; sink and net carbon sink of farmland ecosystems in China costal regions (including ten provinces) with statistic data from 1981 to 2001, which include data of crop yield and agricultural consumptions. Then analyzed the temporal-spatial differences of carbon source, sink and net carbon sink of China costal farmland ecosystems. Secondly, estimated NPP (Net Primary Productivity) of farmland ecosystems in China costal regions with per month NOAA-AVHRR NDVI (Normalized Difference Vegetation Index) data and estimation model. Then the correlation between NPP distribution and the carbon sink of farmland ecosystems was analyzed. At last, this dissertaiton summarized the factors effecting carbon sources and sinks of farmland ecosystems, and put forward several techniques to enhance carbon sequestration and mitigate carbon emission in farmland ecosystems. The results were summarized as follows:(1) There were significant temporal-spatial differences in carbon sources andsinks among different costal regions. Both total carbon absorption and emission of costal farmland ecosystems were increased from 1981 to 2001, but the increasing rate of carbon emission exceeded that of carbon absorption. The total carbon absorption of China costal farmland ecosystems was 15644.2 X 104t in 1981 and increased to 22482.4 X 104t in 2001 with increasing rate of 44%. But the total carbon emission was 1512.86 X 104t in 1981 and increased to 5559.31 X 104t in 2001 with increasing rate of 265%. The total carbon absorption increased from 1981 to the end of 1990's and decreased afterwards, but the total carbon emission increased constantly from 1981. In details, the increasing rate of carbon absorption in Guangxi province was the highest, which in Tianjin and Shanghai city was about zero and was negative in Fujian and Zhejiang. Carbon emission was increasing in all the provinces, among which the increasing rate of Shanghai was the highest. Further, the trend of per area carbon absorption and emission was similar to that of total respectively. In general, per area carbon absorption was about 2-7t/ha, which in Guangxi was the highest among the ten regions. Per area carbon emission was about 0-3t/ha, which in Shanghai was the highest. The results above indicated that the agricultural consumption in developed regions was relatively high.(2) The trend of net carbon sink in costal farmland ecosystem was similar to that of carbon absorption. Net carbon sink was increased by about 20% from 1981 (14122.3 X 104t) to 2001(16923.1 X 104t). It meant that carbon emission was obviously less than carbon absorption in costal regions. For example, carbon absorption was about 3 times more than emission in 2001. The results above showed that the carbon sequestration rate of costal farmland ecosystems was more than 10000X 104t/a ,which meant that there was high carbon sink capacity in China costal farmland ecosystems. But there were also differences among different regions. For instance, the net...