Responses Of Plant Community And Root To Snowpack Change In An Alpine Meadow Of Northwestern Sichuan,China

Seasonal snow cover is a common natural phenomenon in alpine meadow.As the thickness of snow increases,the soil temperature become relatively constant.When the snow start to melt,the soil water content increase.Moreover,with snow cover increasing,plant coverage and soil total phosphorus(P)content will be significantly reduced.Snow cover significantly affects the functional traits of individual plants and plant communities in alpine meadow ecosystem by means of the redistribution of water,nutrients and other resources.However,in the Qinghai-Tibet Plateau,it is rarely reported the influence of snow cover change on alpine meadow plants and communities.In view of such situation,this experiment which was in eastern Qinghai-Tibet Plateau alpine meadow as the research object,by setting the CK(control),S0(remove snow),S1,S2 and S3(natural snow twice,three times,four times)these experimental treatments.The field snow gradient control experiment was carried out by artificial accumulation method.This study analyzed the Qinghai-Tibet Plateau plants,roots,soil physical and chemical properties affected by the snow.The results show that:1.The change in snow cover has a great influence on soil temperature and moisture.The soil temperature decreased and the soil moisture increased with snow cover gradient increasing.S0 reduced soil p H,while S3 increased p H.Moreover,the soil compaction can be significantly improved in S1、S2 and S3.2.S3 can significantly increased the total nutrient in the 0-10 cm soil layer.S2 can significantly increased the total nutrient in the 10-20 cm soil layer.In addition,S1 also promoted total nutrient in soil to some extent,and the available nutrient in soil were higher under the treatment of S1.3.The quantitative characteristics of plant communities have different responses to different snow cover gradient.The total biomass of the community reached the maximum under the treatment of S1.S1 and S2 significantly increased the biomass of sedge.S1 significantly increased the biomass of forbs.S2 and S3 significantly reduced the biomass of grass.Meanwhile,the treatment(S1,S2,S3)significantly reduced the coverage of grass.4.There was a significant positive correlation between the biomass of reproductive organ and individual size of five species,as well as between the biomass of vegetative organ and the biomass of reproductive organ.5.The dynamic changes of root production,root mortality and root standing crop were significantly affected by snow cover.Snowing treatments(S1,S2,S3)delayed the growth peak;S0 and S1 delayed the death peak;S3 delayed the standing crop peak.6.S2 and S3 significantly reduced the root mortality of level 2 in 0-10 cm,S0 significantly reduced the root mortality of level 3.4.5 in 10-20 cm,and S2 significantly increased the root standing crop of level 1 in 0-10 cm.7.Under different treatments,the root production,root mortality and root standing crop of all levels in the 0-10 cm soil layer were higher than that in the 10-20 cm soil layer.With diameter increasing,the production,mortality and standing crop of root decreased successively,while the survival rate of root increased gradually.In addition,the increasing of snow(S1,S2,S3)is conducive to the improvement survival rate of root surviving.8.Through the analysis of structural equation modeling,it is found that the change of snow cover has direct or indirect effects on plant community,root and soil physical and chemical properties.The influence of snow cover on root life,turnover and soil temperature and moisture was significantly.Soil temperature,moisture and nutrients also affect root turnover indirectly through affecting root life span.In summary,seasonal snow directly affects the soil temperature and soil moisture of alpine meadow through repeated freezing and thawing,thus controlling the structure composition of aboveground plant communities and the growth of underground plant roots.The increasing of snow cover alleviates soil water restriction,increases soil nutrient content,prolongs the longevity of roots,but inhibits root turnover,resulting in root standing crop increasing,root mortality decreasing.Due to heterogeneity among plant community species,the growth of different plant speciesallocation policy response to the snow.With the increasing of snow,Saussurea nigrescens and Anaphalis lactea reproductive allocation increases.And the reproductive allocation of Elymus nutans and Koeleria macrantha were lower in S2.S3.The differential response of this growth and reproduction distribution strategy resulted in the insignificant influence of snow cover change on aboveground plant community biomass.On the whole,the above-ground plants and underground roots of the alpine meadow showed "asymmetric response" to the change of snow cover.That is,the influence of snow cover on the underground roots of the alpine meadow was greater than that of the above-ground plant communities.However,the results of this study found that the species diversity of abovementioned plant communities had significant differences in different snow cover gradients,indicating that the change of snow cover had changed the composition of plant communities,and this effect was reflected in plant roots to some extent,and the long-term cumulative effect would eventually be reflected in the productivity of alpine meadow.Therefore,this experiment require to distinguish the response change rules of roots of different plant species,so as to accurately predict the response process of structure and function of alpine meadow ecosystem to the change of snow cover in advance.