Abstract: Based on the statistic data of crop yield and agricultural input in the period from 1981 to 2001,carbon sources and sinks of the farmland ecosystems in the 10 coastal provinces,metropolises and autonomous regions of China were estimated.Conclusions are reached as follows:(1)The total carbon sink of the farmland ecosystem in coastal China was zigzagging upward since 1981,and the total carbon emission climbing rapidly.But comparison shows the former went at a higher rate than the latter.However,the increasing rate(94%) of the indirect carbon emission caused by agricultural input exceeds that of carbon sink(44%) during the crop growing season.(2)Significant temporospatial variation is observed of total carbon sink and emission and of carbon sink and emission per unit area between different regions and among them,both total emission and emission per unit area showed a rising trend with each passing year.The drastic variation of the carbon sink in developed regions is a result of relatively higher agricultural input.The total carbon sink in relatively developed regions showed a downward trend from 1981 to 2001,which indicates that decreased acreage of farmland in the costal regions reduced carbon sink during the crop growing season.(3)The proportion of carbon fixed by the main crops in the farmland ecosystem of the coastal region against that of the whole nation′s was decreasing,which indicates that with the decrease in acreage of cropland and increase in agricultural input,the carbon sink function of the coastal region is weakened.

Key words: coastal region, farmland ecosystem, carbon absorption, carbon emission, carbon source, carbon sink