Yak Dung Decomposition And Its Effects On Soil Physicochemical Characteristics,Microbial Biomass And Enzyme Activities

Yak grazing is a prevalent phenomenon in Qinghai-Tibetan plateau,where there are more than 13.3 million domestic yak,a large proportion of dung directly deposit on the surface of the pasture and become an important source of material and energy for the decomposer.Yak dung is considered as a main way to return nutrients to the grassland.Therefore,the study on yak dung deposition and its decomposition is of great importance for understanding ecosystem function of alpine grasslands in the QinghaiTibet Plateau,especially material and energy cycling.Using artificially simulated dung deposition,we investigated the decomposition of yak dung and its effects on soil physicochemical characteristics,microbial biomass and enzyme activities from July to October 2017.The experiment was conducted at the Alpine Meadow and Wetland Ecosystem Research Station of Lanzhou University(Hezuo research station).The main findings were as follows:(1)During the whole experiment,the percent mass loss was 55.4%,and the content of dissolved organic carbon(DOC)and dissolved organic nitrogen(DON)decreased by 83.2% and 88.4%,respectively.(2)Yak dung addition increased the soil water content and soil dissolved organic carbon(DOC)and dissolved organic nitrogen(DON)concentration,but decreased soil pH.(3)Yak dung addition increased soil microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and microbial respiration(SMR),and decreased the ratio of MBC/MBN.(4)Soil water content did not correlate with soil microbial biomass,while positively correlated with soil microbial respiration;soil pH negatively correlated with soil microbial biomass and soil microbial respiration respectively;Both DOC and DON positively correlated with soil microbial biomass and soil microbial respiration,respectively.(5)Yak dung addition increased enzyme activities which were related with Ccycling and N-cycling,for example,?-1,4-glucosidase,?-1,4-xylosidase,Polyphenol oxidase,Peroxidase and Urease.(6)There was a significant positive relationship between both microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)positively correlated with C and N-cycling enzymes;Microbial respiration(SMR)did not correlated with C-cycling enzymes,while positively correlated with N-cycling enzyme.In conclusion,the yak dung deposition increased the supply of soil nutrients and promoted the growth and activity of soil microorganisms.Therefore,yak dung deposition accelerates the nutrient cycling of the alpine grassland ecosystem and facilitate the maintenance of the alpine ecosystem in the Qinghai-Tibet Plateau.