Effects of C and N disturbances on the decomposition of leaf litter of forests were studied in situ through adding sugar and nitric ammonium to 4 forestlands and leaf litter decomposition experiments in the upper reach area of Mingjiang river

Sichuan province.The results showed that the annual decomposition ratios of leaf litter in the 4 artificial forests were Betula utilis(0.449 7)>Cercidiphyllum japonicum(0.271 0)>Picea asperata(0.259 4)>Pinus yunnansinsis(0.236 5).Mild disturbances of C and N on the forestlands of Cercidiphyllum japonicum and Pinus yunnansinsis have improved the activities of microorganisms in soil and accelerated the decomposition of leaf litter

but strong disturbance of N was not beneficial to further advance of the decomposition and strong disturbance of C even restrained it.For Betula utilis

both C and N disturbances have led to the decrease of litter decomposition ratio. This meant that the microorganisms in the forestland of Betula utilis were short of C and N.In addition

both C and N disturbances with different strength on the forestland of Picea asperata have accelerated the decomposition of leaf litter and mild disturbances of C and N are better than strong disturbances for acceleration.This indicated that the microorganisms in forestland of Picea asperata were short of C and N.