Study On Distribution Characteristics Influencing Factors Of Earthworms In Typical Regions Of Yunnan

Earthworms,as one of the large soil animals,which play an extremely important ecological function.As a province with great biodiversity,Yunnan Province contains extremely rich biodiversity.Many studies tend to analyze its biodiversity,but there is no specific research on the biodiversity and distribution characteristics of earthworms.In this paper,through the method of quadratic survey,Yunnan is divided into 6 different climate types,and representative land use types are selected under each climate type to collect earthworm and soil samples.At the same time,the distribution characteristics of earthworm species,density and biomass in typical regions of Yunnan were analyzed.Then quantitatively analyzed the relationship between distribution of earthworms and environment factors through structural equation modeling.The research results show:(1)A total of 1,984 earthworm samples were collected from 149 sample sites,and27 species(subspecies)of earthworms were found in 4 families,11 genera,including Megascolecidae,Lumbricidae,Moniligastridae and Glossoscolecidae.From this research,we clearly found that Megascolecidae as the dominant vermiidae in this study regions,the Octolasion tyrtaeum Savigny,1826 and Aporrectodea trapezoids(Duges,1828)were the dominant species.(2)There were obvious differences in the distribution of earthworms in soil under the 7 climatic types.Earthworm species temperate zone>north tropic zone>north subtropical zone>middle subtropical zone>plateau climate zone>south subtropical zone;Earthworm density plateau climate zone>temperate zone>northern subtropical zone>north tropic zone>middle subtropical zone>southern subtropical zone;Earthworm biomass northern subtropical zone>northern tropic zone>south subtropical zone>temperate zone>middle subtropical zone>plateau climate zone.Among them,altitude and temperature had significant effects on earthworm density(P<0.0001)and biomass(P=0.029),respectively.(3)There were obvious differences in the distribution of earthworms under the 4typical land use types,earthworm species arable land>orchard>grassland>wasteland;Earthworm density wasteland>arable land>orchard>grassland;Earthworm biomass orchard>wasteland>arable land>grassland.Land use types mainly affect the distribution of earthworms through changes in soil physical and chemical properties.By constructing a structural equation model,it is found that soil physical and chemical properties have differences in the distribution of earthworms.The contribution of soil physical properties to earthworm biomass is 0.213(P<0.05),where soil porosity,soil temperature and soil water content played a major role;the contribution of soil chemical properties was 0.163(P<0.05),which played a role in soil organic matter,total nitrogen and available phosphorus.Earthworm biomass was a significant positive correlation with total nitrogen and organic matter(P<0.05),and a very significant negative correlation with available phosphorus(P<0.01).It can be seen that the contribution to earthworm biomass is that soil physical properties are greater than chemical properties.In addition,the earthworm density was mainly affected by soil chemical properties,with a contribution of 0.391(P<0.001),among which p H,total potassium and available phosphorus played a significant role,and the effect of available phosphorus was extremely significant(P<0.001).(4)There were differences in soil heavy metal content among different land use types,but its influence on the distribution of earthworms was lower than other factors.In this study,the soil has the risk of heavy metal pollution of Cr and Zn.The content of Cr and Zn is significantly higher than the risk value of Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard(Trial)(GB15618-2018).Earthworm density was affected by soil heavy metal content,which had a significant linear negative correlation with Mn(R~2=0.044,P=0.01),and had no significant effect on earthworm biomass.To sum up,the research results show that the climate type,land use type and heavy metal content are the main factors affecting the distribution of earthworms.The climate type mainly depends on altitude and temperature to affect the composition of earthworm community,among which altitude has a significant positive effect on earthworm density(R~2=0.39,P<0.0001),but has no significant effect on earthworm biomass;temperature with earthworm biomass have a significant positive correlation(R~2=0.11,P=0.029),while the effect on earthworm density was not significant.The content of heavy metals had no significant effect except that Mn and earthworm density showed a significant negative correlation.Whether it is climatic factors,heavy metals or land use types,all influence on the distribution of earthworms,and the most significant impact is the land use type,which mainly affects the life and survival of earthworms by changing the environment in which they live.Through regression analysis,it was found that the density of earthworms was closely related to soil organic matter(P=0.001),total nitrogen(P=0.033),alkali-hydrolyzed nitrogen(P=0.001),total phosphorus(P=0.001),available phosphorus(P=0.001)and available potassium(P=0.001)were significantly positively correlated,while the effect on earthworm biomass was not significant.Through research on the distribution of earthworm diversity in typical areas of Yunnan,to grasp its distribution characteristics,influencing factors and mechanisms,in order to quantitatively analyze the factors affecting the distribution of earthworms and their contribution.Which provides data support and theoretical basis for play ecological functions of earthworms and related polluted soils environmental animal restoration.