Effects Of Yak Dung Decomposition On Plant Community Characteristics And Soil Microenvironment Of Alpine Meadow In Northwest Sichuan,China

Yak grazing in the alpine meadow on the Qinghai-Tibet plateau has a history of thousands of years.However,in order to meet the needs of production and life,local herdsmen have removed a large amount of yak dung from the grassland ecosystem for a long time,which makes it impossible for nutrients to return to the soil for recycling,which has a certain impact on the plant-soil-microorganism in the alpine grassland ecosystem and may increase the ecological risk.To investigate yak dung after removing the response of the alpine meadow ecosystem,this study in northwest Sichuan alpine meadow under the background of natural grazing yak dung spot distribution on the basis of simulation set up warm season?May?and cold?December?yak dung deposition experiment,effects of yak dung decomposition of plant community,soil physical and chemical properties,soil enzyme activity and soil microbial community as well as the mechanism of action,for the region's yak dung treatment formulating appropriate management measures,to maintain the local function of grassland ecosystem balance and stability is of great significance.The results show that:1.During the warm season,the decomposition of deposited yak dung significantly increased the biomass of grass,sedge and total aboveground biomass,but decreased the biomass of legume and forbs grasses.Decomposition of deposited yak dung in cold season still increased the biomass of grass plants,but decreased the total biomass of legume and forbs plants.In addition,the decomposition of deposited yak dung in both warm and cold seasons had no significant effect on plant community diversity.2.The accumulation of yak dung is beneficial to the improvement of soil physical and chemical properties in alpine grassland.The total soil nutrients?TC,TN,TP?,available nutrients?NH₄⁺,NO₃^-,AP?,soil water moisture and pH were increased by the decomposition of yak dung.With yak dung as the center radiating outwards,the decomposition of deposited yak dung in warm season can significantly increase the contents of TC and TN in the soil under the dung block.However,the decomposition of deposited yak dung in the cold season continued to have an effect on the soil within a range of 20 cm around the dung block,significantly increasing the content of available nutrients.3.The yak dung decomposition significantly increased soil invertase C-?-glycosidase enzymes?BG?,peroxidase?PER?and phenol oxidase?PPO?activity and N invertase-?-N-acetyl glycosidase enzymes?NAG?and the activity of protease?LAP?,and the longer the distance the yak dung as the center outward radiation,soil enzyme activity response is weak,the soil enzyme activity of the most significant under the dung.4.For bacteria,the dominant phyla of the bacterial community in the alpine meadow soil of this research area are Proteobacteria,Actinobacteria and Acidobacteria.With the treatment of yak dung,the relative abundance of Proteobacteria and Actinobacteria increases significantly,while the relative abundance of Acidobacteria decreases significantly.For fungi,the dominant fungi in the soil community were Ascomycota and Basidiomycota.The relative abundance of Ascomycota increased significantly after yak dung treatment,while the relative abundance of Basidiomycota decreased significantly.5.For bacteria,the decomposition of deposited yak dung in warm season has no significant effect on the diversity of soil bacterial community,but the short-term decomposition of deposited yak dung in cold season will improve the diversity of soil bacterial community,while the long-term decomposition has no significant effect on the diversity of bacterial community.For fungi,short-term decomposition of yak dung deposited in warm season can improve the diversity of fungal community,but long-term decomposition can reduce the diversity of fungal community.The short-term decomposition of yak dung in cold season would lead to the decrease of fungal community diversity,but the long-term decomposition had no significant effect on the fungal community diversity.6.The results of Redundancy analysis?RDA?showed that,as for the impact of yak dung decomposition on the composition of soil bacterial community,the decomposition of deposited yak dung in warm season mainly depends on soil SM and TN in the short term,and on soil NO₃^-in the long term.In the short term,soil TC,C/N and NH₄⁺were used to deposit yak dung in the cold season,while in the long term,soil TC and NH₄⁺were used to deposit yak dung.However,as for the impact of yak dung decomposition on the composition of soil fungal community,the main factors for the decomposition of yak dung in the warm season are soil AP in the short term,while the long-term factors are soil pH,SM,NH₄⁺and NO₃^-.In the short term,the decomposition of deposited yak dung mainly depends on soil TC and AP,while in the long term,it depends on soil pH.7.The results of Structural Equation Model?SEM?showed that:During the decomposition of yak dung in warm season,the decomposition period and soil pH significantly affected the diversity of fungus community.In the decomposition of deposited yak dung in cold season,the diversity of bacterial community was mainly affected by the decomposition cycle and the activity of BG enzyme,while the diversity of fungal community was mainly affected by the decomposition cycle.In summary,the decomposition of yak dung indirectly changes the composition and diversity of bacterial and fungal communities by changing the physical and chemical properties of the soil.The decomposition of yak dung was beneficial to increase the relative abundance of eutrophic flora?such as Proteobacteria,Actinomycetes and Ascomycetes?,and to decrease the relative abundance of eutrophic flora?such as Acidobacteria and Basidiomycetes?.However,the decomposition of deposited yak dung in different seasons has different effects on the diversity of soil microbial community.The deposition of yak dung in warm season mainly affects the diversity of fungal community,while that in cold season mainly affects the diversity of bacterial community.Therefore,the decomposition process of deposited yak dung in warm season is mainly completed by the fungal community,and the decomposition function of the fungal community becomes"specialized"with the increase of the decomposition process,which is not conducive to maintaining the stability of the fungal community.On the other hand,the decomposition of deposited yak dung in the cold season occurs in the alternate season of winter and spring,which is in the period of nutrient deficiency of soil,and the enzyme activity is relatively inhibited,which intensifies the resource competition of bacteria and fungi community,and enables the bacterial community with the ability to efficiently utilize nutrients to be in a dominant position.However,this may inhibit the germination of some beneficial fungi?such as arbuscular mycorrhizal fungi?on plant roots in the early growing season,thus affecting plant community productivity.In addition,the improvement of the diversity of soil bacteria community can to some extent make up for the ability of plants to absorb soil nutrients,and the complementary ecological functions of bacteria and fungi community are conducive to maintaining the balance of C and N and the stability of functions of grassland ecosystem.