Abstract: Yak grazing could significantly affect soil environments by changing the transformation and transportation of soil nitrogen, with consequences on primary production of alpine wetland ecosystems. However, little is known about the effects of yak excreta addition on soil nitrogen transformation in peatlands of northwestern Yunnan. In this study, the effects of yak excreta addition on nitrogen transformation of peatland soil was measured in a controlled experiment using soil cores collected from a typical peatland in northwestern Yunnan. The results showed that the addition of yak dung and urine promoted the accumulation of NH₄⁺-N at the early stage. The NH₄⁺-N content was reduced in peatland soil with excreta addition during the whole incubation, but the NO₃^--N content was increased, indicating that nitrification was the dominant process. The addition of dung and urine significantly increased urease activity in peatland soil, but reduced denitrifying enzyme activity (P<0.05). The addition of dung enhanced the activities of catalase and N-acetylglucosaminidase (P<0.05), while the addition of urine inhibited the activity of N-acetylglucosaminidase (P<0.05). The effects of dung addition did not affect nitrogen mineralization and nitrification (P>0.05), but urine addition significantly affect nitrification during the incubation (P<0.05). Dung addition inhibited, but urine addition promoted denitrification during the incubation. Changes in soil physicochemical pro perties and enzyme activities with yak excreta addition play an important role in altering denitrification in peatland soil.

Key words: excreta addition, peatland, mineralization, nitrification, denitrification.