N biogeochemical cycle and its impacts on environments in an agro-forest ecosystem

The N balance and its pollution characteristics on environments in a typical agro-forestry ecosystem in the up-per reaches of the Yangtze River were studied．The results show that in ecosystem，there is relatively high N surplus in croplands，almost N balan ce in paddies and high N deficit in forest．N balance apprmsals show the N balance rate of crop-lands is reasonable but that of paddies shows a little hi ghcr．However，N balance of the whole arable lands has changed greatly from heavy deficit of 1960s tO reasonable balance of nowadays ．Forest and cultivations play the impo rtant roles in the N balance changes of ecosystem ．But the great increases chemical N fertilizer usages lead to the increasing of the gas N emissions and N non-po int source pollutions risk of water bodies．