Effects Of Robinia Pseudoacacia On Soil Microbial Diversity And Community Structure In Loess Hilly And Gully Region,China

The Loess Plateau is well known for severe soil erosion.To control the soil erosion and improve eco-environment,the government has issued a series of projects for ecological restoration including ―Grain for Green‖ project.With the implementation of these projects,the environment has been greatly improved.Robinia pseudoacacia(black locust)has been widely planted as pioneer species.Although it has brought positive effects on environmental improvements,the plantations may have not developed well in some sites,and cannot produce expected results.Soil microbiome,an integral component of ecosystems,involves in all soil processes,and the microbial abundance,diversity and community structure have significant impact on soil status.Comparison of soil microbial diversity and community structure between black locust forest and native communities along environmental gradient may provide important clues on ecological impact of exotic species Robinia pseudoacacia on local ecosystems.In this study,we used the Biolog technique and high-throughput sequencing technologies to investigate the changes in soil microbial diversity and community structurebetween black locust forest and native communities along environmental gradient.The results are as follows:(1)Introduction of black locust generated a large variation in soil microbial functional diversity in different vegetation zones.The trend of Average Well-Color Development(AWCD)and functional diversity indices in black locust forest were similar from the steppe to forest zones.The value of the AWCD and functional diversity indices of black locust forest,including Richness Index(S),Shannon-Weiner index(H),Simpson index(D),and Mc Intosh index(U),were larger than native communities in steppe and forest-steppe vegetation zones,while lower than native communities in forest zone.Significant differences in the utilization of carbon sources were found,particularly in terms of the utilization of carbohydrates and amino acids by microbial organisms between black locust forest and native communities.Principal Component Analysis(PCA)analysis indicated that the numbers of carbon sources loaded on PC1 were 24.Carbohydrates,amino acids,and carboxylic acids played major roles in the separation of principal components.The soil microbial functional diversities were affected by the content of soil carbon and nitrogen,and carbon source utilization patterns were influenced by temperature and humidity.(2)The introduction of black locust also brought a large variation in soil bacterial diversity and community structure in different vegetation types along environmental gradient.The dominant bacterial phyla were Acidobacteria,Proteobacteria,Planctomycetes,Chloroflexi and Actinobacteria in study area.The relative abundance of Acidobacteria and Proteobacteria was greater in the forest zone than in steppe and forest-steppe vegetation zones while Actinobacteria was less abundant in the forest vegetation zone than in the other two vegetation zones.In forest and forest-steppe zones,compared to native communities,the relative abundance of Acidobacteria and Planctomycete was higher in native communities species than in black locust forest while Actinobacteria was more abundant in black locust forests than in native communities.In steppe zone,the relative abundance of Acidobacteria,Planctomycete and Actinobacteriawas opposite to changes in forest and forest-steppe zones.The bacterial diversity indices were the greatest in forest-steppe vegetation zone,and the smallest in forest vegetation zone.The Chao index and ACE index of black locust were greater than native communities in forest-steppe and forest vegetation zones.However,the Chao index and ACE index of black locust were smaller than native communities in steppe vegetation zones.The bacterial community structure was mainly influenced by climate factors and soil properties other than soil phosphorus content.The results suggested that environmental gradient and differences in vegetation type lead to changes in soil chemical properties and control the composition of microbial communities in the semi-arid Loess Plateau region.(3)Introducing black locust into different vegetation zones generated a large variation in soil fungal diversity and community structure in different vegetation types.In study area,the dominant fungal phyla were Ascomycota and Basidiomycota.The dominant fungal classes were Dothideomycetes,Eurotiomycetes,Leotiomycetes,Sordariomycetes and Agaricomycetes.The relative abundance of Ascomycota in all vegetation zones was higher in black locust forest than in native communities in all vegetation zones.However,in all vegetation zones the relative abundance of Basidiomycota was smaller in black locust forest than in native communities.The fungal diversity showed no significant difference among vegetation zones as well as between black locust and native species.However,the fungal diversitywas highest in native communities in forest-steppe zone.The fungal community structure was mainly influenced by climate factors and soil properties,especially soil water content,soil total carbon and soil total nitrogen.