Carbon fixation by farmland ecosystems in China and their spatial and temporal characteristics

The amount of carbon fixation and its spatial and temporal characteristics by farmland ecosystem are estimated and analyzed ．The results show that the total quantities of carbo n fixation increases gradually in the past two decades be-cause the carbon density per hectare increases．The East China belongs tO the area of the high value(over 3t／hm² )and the agropastural ecotone in North China has the low value of carbon density which is less than 1t／hm² ．Thus，the cropresidue management is the key issue for enhancing carbo n sequestration．