Effects Of Artificial Vegetation Restoration On Soil Microbial And Nematode Community In Southern Ningxia Mountain Area

The Loess Plateau is known as one of the most seriously eroded and fragile ecological areas in China.As an important measure of vegetation construction in the Loess Plateau,artificial vegetation restoration plays an important role in the improvement of ecological environment in this area.Microorganisms and nematodes occupy the key position of soil food web,which have important influence on organic matter decomposition,nutrient circulation and other ecological processes,and can indicate the restoration of soil ecosystem.In this study,we selected soils under different types of artificial vegetation(Medicago sativa artificial grassland,Caragana korshinskii plantation and orchard),and those under artificial grasslands(1,2,6,12 years)and artificial shrub forests(4,14,24,34 years)with different cultivation years in southern Ningxia mountain area,as the research objects,to investigate the composition,structure and diversity characteristics of soil microbial and nematode communities.The aim of this thesis is to explore the changing law,mutual relationship and influencing factors of soil microbial and nematode communities during restoration of artificial vegetation in loess hilly area.The results showed that :(1)Compared to farmland,all the three types of artificial vegetation significantly increased the abundance of soil fungi and nematodes,and the increase extents were manifested as artificial forest land > artificial grassland > orchard.Caragana korshinskii artificial forests and Medicago sativa artificial grassland significantly reduced the proportion of herbivorous nematodes and increased the maturity index and structure index of nematode community,leading to significant improvement in the abundance and structure of soil microorganism and nematode community.The effect of Caragana korshinskii shrub forest was more significant than that of Medicago sativa artificial grassland,with its microbial and nematode communities were similar with those in natural grassland.RDA analysis results showed that soil organic carbon and total nitrogen were the main factors affecting soil microbial and nematode communities.The abundance of fungi and nematodes were positively correlated,while the dominant bacterial flora and bacterial commmunity diversity significantly affect the trophic group composition,maturity index and organic matter decomposition pathway of nematode communities.(2)The abundance and diversity of soil bacteria were significantly higher in Medicago sativa artificial grasslands than those in farmland.With the increase of cultivation years of Medicago sativa grassland,the Chao1?ACE and Shannon diversity index of soil bacterial community gradually increased,which reached the highest in the sixth year after planting Medicago sativa and then decreased.Soil nematode abundance showed a similar changing trend.The proportion of bacterial-feeding and herbivorous nematodes increased with the cultivation years of Medicago sativa grassland,while the proportion of fungal-feeding nematodes and omnivorous/predatory nematodes decreased continuously.The results of nematode faunal analysis showed that Medicago sativa cultivation significantly improved the structure of soil food web,which was the most mature and stable in the sixth year after Medicago sativa planting.However,the rapid increase of root biomass in this period led to the substantial increase of herbivorous nematode proportion and the significant decrease of nematode diversity index,which may be the important reason for deterioration of soil nutrient enrichment and degradation of artificial grassland in the later development stage.RDA analysis results showed that soil available phosphorus and root biomass were the main factors affecting soil microbial and nematode communities.Bacterial community composition and diversity significantly affected the trophic group composition,diversity,maturity,and organic matter decomposition pathways of nematode communities,while fungal diversity was significantly positively correlated with the proportion of fungal-feeding nematodes.(3)Soil bacterial abundance,Chao1 and ACE index and nematode abundance decreased at the initial restoration stage of Caragana korshinskii plantation,then increased until reaching the highest level in the 14 th yeat,and finally decreased again.At the initial restoration stage of Caragana korshinskii plantation,the proportion of bacterial-feeding nematodes was higher.With the increase of cultivation years of Caragana korshinskii plantation,the proportion of omnivorous/predatory nematodes increased continuously and reached the highest after 14 years of vegetation restoration,as well as structure index and maturity index of nematode community.However,in the 24 th year after Caragana korshinskii planting,the increase of root biomass led to a significant increase in the proportion of plant-feeding nematodes and the plant parasitic nematode index,while the proportion of omnivorous/predatory nematodes and maturity index of nematode community decreased,indicating that soil food web was seriously disturbed.RDA analysis results showed that soil organic carbon is the main factor affecting the composition of microbial and nematode communities,and its content is usually closely related to plant diversity and biomass.The results of correlation analysis showed that the abundance and diversity of bacteria were negatively correlated with the dominance index of nematode community,while the abundance of fungi was positively correlated with the abundance of nematode,and negatively correlated with the proportion of bacterial-feeding nematodes and Wasilewska index.(4)Effects of vegetation type and restoration years on plant growth characteristic and community composition can further cause changes in soil microbial and nematode community composition by affecting their food resource status.During vigorous growing stage of artificial vegetation,the rapid increase of root biomass and the significant decrease of plant diversity can lead to a substantial increase in the proportion of plant-feeding nematodes,which further negatively affect soil biodiversity,and food web function and stability,probably resulting on the degradation of aritificial vegetation.Therefore,it is of great significance to take reasonable measures to inhibit plant-feeding nematodes for artificial vegetation restoration.