N biogeochemical cycle and its impacts on environments in an agro-forest ecosystem
农林复合生态系统氮素生物地球化学循环及其环境影响研究

The N balance and its pollution characteristics on enviro nments in a typical agro -forestry ecosy stem in the upper reaches of the Yangtze River were studied.The results show tha t in ecosystem,there is relatively high N surplus in croplands,almost N balance in paddies and high N deficit in forest. N balance appraisals show the N balance rate of croplands is reasonable but that of paddies shows a little higher.Howeve r,N balance of the whole arable lands ha s changed greatly from heavy deficit of 1960s to reasonable balance of nowadays. Forest and cultivations play the importa nt roles in the N balance changes of eco system.But the great increases of chemic al N fertilizer usages lead to the incre asing of the gas N emissions and N non -p oint source pollutions risk of water bod ies.