| In order to understand and master the overall features,community characteristics and spatial and temporal changes of soil fauna in the Nianchu River Basin,provide basic data for the study of soil fauna diversity and ecological function,and provide scientific basis for the protection of the ecosystem and sustainable development in this region.According to the special geographical location and vegetation types in the Nianchu River Basin,four major habitat types were selected,including grassland（CD）,wetland（SD）,farmland（NT）and sea-buckthorn forest（SJ）,and three sampling times were carried out in May,August and October of 2020.CD set a total of 4 first-level quadrats and 20 sampling points,a total of 25 sampling sites in 5 first-grade quadrats were set up in farmland（NT）,wetland（SD）and seabuckthorn shrub（SJ）,and a total of19 first-grade quadrats were set up with 95 sampling sites.In each firstgrade quadrat,the surface and underground soil macrofauna（0-10cm）were collected by hand and stored in a sealed tube containing 75%alcohol for later use.Longitude and latitude,altitude（Alt）,soil temperature（ST）and soil water content（SWC）were recorded at same time.Soil samples were collected by a soil collector according to the five-point pattern of plum blossom.Five small soil samples were randomly collected from each secondary sample square,and a total of 25 small soil samples were collected.After mixing,they were put into breathable cloth bags and brought back to the laboratory for separation and identification.Soil meso-microfauna were separated by modified Tullgren dry funnel.After 48 hours of separation,the collected soil meso-microfauna were put into glass bottles containing 75% alcohol.And then,the soil fauna was identified by Leica type microscope,and the number of individuals and groups was recorded at same time.Other soil physical and chemical factors（p H,total nitrogen（TN）,soil water content（SWC）,available potassium（RAK）and soil organic matter（SOM））were determined by Xizang Boyuan Environmental Testing Co.,Ltd.Among the 19 first-grade quadrates of different habitat types in the Nianchu River Basin,the following results were obtained by sampling in spring,summer and autumn:（1）A total of 4,661 soil macro and meso-microfauna were captured,belonging to 72 classes 51 families,27 orders,7 classes and 3 phyla.At the phylum level,Arthropoda was the dominant phyla,accounting for80.09% of the total catch.In class level classification,Insecta was the dominant class,accounting for 43.10% of the total catch.There were 5dominant orders at order level.These orders were Basommatophora,Hymenoptera,Coleoptera,Prostigmata and Araneida,respectively,accounting for 69.86% of the total catch.There were 9 common orders,accounting for 23.95% of the total catch,and 15 rare orders,accounting for 6.19%.In general,the dominant groups were Lymnaeidae,Prostigmata and Formicidae,accounting for 39.13% of the total catch.There were 15 common taxa,accounting for 43.89% of the total catch,and 53 rare taxa,accounting for 10.89% of the total catch.（2）In spring,the functional groups of soil fauna were mainly predatory,omnivorous,scavenging,and plantophagous,accounting for42.46%,40.12%,10.66% and 6.59% of the total catch.In summer,the main functional groups of soil fauna were predatory（Pr）,omnivorous（O）,herbivorous（Ph）and scavenging（S）,accounting for 45.17%,37.14%,9.79% and 7.62% of the total catch.Predacious（Pr）,omnivorous（O）,herbivorous（Ph）and scavenging（S）soil fauna were the main functional groups in autumn,accounting for 45.11%,32.51%,17.60% and 4.77% of the total.（3）There were no significant differences in the number of individuals and groups of soil fauna in grassland among three seasons（P>0.05）.There was no significant difference in individual number of soil fauna in farmland habitat among three seasons（P>0.05）,but the group number of soil fauna in farmland habitat was significantly different among three seasons（P<0.001）.There were no significant differences in the number of individuals and groups of soil fauna in wetland habitat among three seasons（P>0.05）.There were no significant differences in individual number and group number of soil fauna in seabuckthorn forest among the three seasons（P>0.05）.There were no significant differences in diversity index（H）,evenness index（E）and dominance index（C）of soil fauna in grassland among three seasons（P>0.05）.The diversity index（H）of farmland of soil fauna in grassland had significant difference among seasons（P<0.05）,the evenness index（E）of farmland of soil fauna in grassland had no significant difference among seasons（P>0.05）,and the dominance index（C）of farmland of soil fauna in grassland had significant difference among three seasons（P<0.05）.There were no significant differences in diversity index（H）,evenness index（E）and dominance index（C）of soil fauna in wetland among three seasons（P>0.05）.There were no significant differences in diversity index（H）,evenness index（E）and dominance index（C）of soil fauna in seabuckthorn forest among the three seasons（P>0.05）.（4）Analysis of common and endemic groups in four different habitat types and among different sites showed that SD2 site had the lowest number of soil fauna and SD5 site had the highest number of soil fauna.The total number of soil fauna in the four habitat types was 20.Jaccard similarity results of soil fauna in different habitat types showed that,the similarity coefficient between the soil fauna communities in spring ranged from 0.29 to 0.43,indicating moderate dissimilarity.In summer,the similarity coefficient between the soil fauna communities ranged from 0.40 to 0.57,which was moderately dissimilar to moderately similar.The similarity coefficient between the soil fauna communities in autumn ranged from 0.36 to 0.56,indicating moderate dissimilarity to moderate similarity.The results of principal coordinate analysis（PCOA）showed that CD,SD and NT had high similarity among three seasons,while SJ had high similarity with NT in summer and autumn.（5）There were no significant differences in soil temperature（ST）,soil water content（SWC）,total nitrogen（TN）and soil organic matter（SOM）between seasons（P>0.05）.There were significant differences in p H between seasons（P<0.001）.There were significant differences in available phosphorus（AP）between seasons（P<0.05）.There were significant differences in available potassium（RAK）between seasons（P<0.001）.There was no significant difference in available potassium（RAK）among the 19 samples,but there were significant differences in other physical and chemical factors.（6）There was an extremely significant negative correlation between Altitude（Alt）and the number of groups（N）in spring（P<0.01）.Soil water content（SWC）was significantly positively correlated with the number of individuals（n）（P<0.05）.There was a significant negative correlation between available phosphorus（AP）and diversity index（H）（P<0.05）.Altitude（Alt）was significantly negatively correlated with diversity index（H）and dominance index（C）in summer（P<0.01）.There was a significant negative correlation between total nitrogen（TN）and diversity index（H）and dominance index（C）（P<0.05）.The available potassium（RAK）was significantly negatively correlated with diversity index（H）,dominance index（C）and evenness index（E）（P<0.05）.There was a significant positive correlation between soil organic matter（SOM）and number of individuals（n）（P<0.05）,and there were a significant negative correlation between soil organic matter（SOM）,diversity index（H）and dominance index（C）（P<0.05）.Altitude（Alt）was significantly negatively correlated with the number of group（N）in autumn（P<0.01）.Available phosphorus（AP）was a significant explanatory variable with an explanatory rate of 37.7%,which was the main environmental factor in spring.Available phosphorus（AP）and p H were significant explanatory variables with explanatory rates of 16.1% and 14.9%,which were the main environmental factors in summer.Altitudes（Alt）,p H,total nitrogen（TN）and available phosphorus（AP）were significant explanatory variables with explanatory rates of 11.9%,7.1%,7.4% and 8.1%,respectively,which were the main environmental factors in autumn.In conclusion,the dominant groups of the four habitat types（CD,SD,NT and SJ）were Lymnaeidae,Prostigmata and Formicidae in spring,summer and autumn.The main functional groups were predatory animals（Pr）,followed by omnivorous animals（O）.The food web of the ecosystem was more complex,and the ecosystem had strong resistance to external disturbance,and the system stability was strong.There was no significant difference in the number of individuals of soil fauna among the four habitat types,but there was no significant difference in the number of groups of soil fauna among the four habitat types except farmland（NT）,indicating that there was little change in the number of individuals and groups of soil fauna between the seasons.There were no significant differences in the diversity indices of soil fauna of CD,SD and SJ habitat types between the seasons,indicating that the community characteristics of soil fauna did not change significantly between the seasons.The diversity index（H and C）of NT soil fauna was significantly different between seasons,but the evenness index（E）was not significantly different between seasons（P>0.05）.The spatial distribution of soil fauna community characteristics was heterogeneous and the spatial similarity was low.Altitude（Alt）was negatively correlated with the number of groups（N）,soil water content（SWC）was positively correlated with the number of individuals（n）,and available phosphorus（AP）was negatively correlated with diversity index（H）.Altitude（Alt）was negatively correlated with diversity index（H）and dominance index（C）,while total nitrogen（TN）,soil organic matter（SOM）and available potassium（RAK）were negatively correlated with diversity index（H）and dominance index（C）,and soil organic matter（SOM）was positively correlated with the number of individuals（N）.Altitude（Alt）was negatively correlated with the number of groups（N）in autumn.Available phosphorus（AP）was the main environmental factor in spring.Available phosphorus（AP）and p H were the main environmental factors in summer.Altitude（Alt）,p H,total nitrogen（TN）and available phosphorus（AP）were the main environmental factors in autumn. |
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