| The habitats in the hilly and gully regions of the Loess Plateau are fragile.But after large-scale return of farmland to forests and grassland projects,the vegetation coverage rate has been significantly improved,and soil erosion problems have been effectively controlled,and there are many breakthroughs in ecological restoration and ecological management of the Loess Plateau.In order to study the soil microbial community structure and diversity in different returned woodland,this research used space instead of time method to select Hippophae rhamnoides forest,Robinia pseudoacacia forest,Hippophae rhamnoides × Robinia pseudoacacia mixed forest,Hippophae rhamnoides × Armeniaca sibirica mixed forest,Robinia pseudoacacia × Armeniaca sibirica mixed forest separately in 10,17,24 years and the grassland of 30 years of afforestation as research objects.The purpose of this paper is to clarify the spatial distribution characteristics of soil microbial communities in Wuqi forest region by using high-throughput sequencing technique,and to analyze the changes of soil bacterial and fungal community structure in different forest structures.The internal mechanism of soil microbial community,macro-meso soil animal community and soil physical and chemical factors was expounded in order to provide data support for biodiversity evaluation of vegetation restoration region in the Loess Plateau from the perspective of soil microorganism.At the same time,it provided the basic data of microorganism for the comprehensive ecological environment management of the Loess Plateau in the new era.The main findings are as follows:(1)A total of 36 phyla,88 classes,112 orders,217 families,and 312 genera of bacteria were detected,mainly including Proteobacteria,Actinobacteria,and Acidobacteria.The structure of bacterial communities in different forests was different.With the increase of returning time,the relative abundance and species of dominant bacterial groups in pure and mixed forests changed.The bacterial community diversity of the five types of forest land increased with the increase of the time of returning farmland.Under the same period of returning farmland,the bacterial community diversity of pure forest land was lower than that of the mixed forest.The soil bacterial community richness in the cultivated forest land will be affected by the time of returning farmland and forest structure.The species diversity of soil bacterial communities in different forest land tended to be stable after a certain period of time;the difference of soil bacterial community composition between different forest land was different,and the difference of soil bacterial community composition between different forest land of the same returning time was significant(P<0.05);With the increase of the time,the difference of soil bacterial community structure decreased in forest lands of the same returning farmland.(2)A total of 6 phyla,28 classes,88 orders,194 families,302 genera of fungi were detected in different returning forest soil.The dominant groups were Ascomycota,Zygomycota and Basidiomycota.The relative content of ascomycetes in pure forest decreased with the increase of returning time,and the relative content of ascomycetes in mixed forest increased with the increase of returning time.The species and relative abundance of fungi,the structure and size of fungi community were different in the soil fungal community of the recultivated forest land.The difference between the structure of the soil fungus community of the Robinia pseudoacacia forest with different returning time was the largest;the difference between soil fungal community structure of Hippophae rhamnoides × Armeniaca sibirica mixed forest in different returning time was the least.The variation of the relative abundance of the different groups of the fungi in the same stand was different with the increase of returning time.The diversity of soil fungal community in different plots was different,and the variation of soil fungal community diversity in the same stand was different with the increase of time.The diversity of soil fungal community in the mixed forest was larger than that of pure forest of the same returning time.(3)A total of 425 macro-meso soil animals were captured in different returning woodlands in Wuqi,belonging to 2 phyla,7 classes 22 orders and 40 classes,most of which were Coleoptera,Hymenoptera and Homoptera individuals.Different dominant groups of macro-meso soil animals adapted to different living environment,and also had different responses to various environmental conditions.The diversity and heterogeneity of large-sized and medium-sized soil animal communities in mixed forest were higher than those in pure forest,and the recovery effect of mixed forest model on other organisms in the study area was greater than that in pure forest.The canonical correlation analysis showed that the individual number and species evenness of macro-meso soil animal communities had the greatest influence on the distribution of soil bacterial communities.The individual number,species evenness and species diversity of macro-meso soil animal communities had the greatest influence on the distribution of soil fungi communities.Spearman correlation analysis showed that there was a significant negative correlation between the number of individuals in macro-meso soil animal communities,the diversity index of soil bacterial community,and the depth index of sequencing(P<0.05).There was a significant positive correlation between the species evenness index of macro-meso soil animal communities and the depth index of soil bacterial community sequencing(P<0.01).There was a significant positive correlation between the species evenness index and the depth index of fungal community sequencing in macro-meso soil communities(P<0.05).(4)There were differences in soil physical and chemical factors among the forest lands in the study area.Soil moisture content,soil organic matter and soil total potassium had a great influence on the distribution of bacterial and fungal communities.At the level of phylum,order and family,the distribution of soil bacterial community was related to the comprehensive effect of soil organic matter,total nitrogen,total phosphorus and total potassium,and there was a linear relationship between them(r=0.250,P=0.011,r=0.209,P=0.047,r=0.213,P=0.047).At the phylum level,there was a significant correlation between soil bacterial community and soil physical and chemical factors,which was a linear relationship(r=0.256,P=0.009).The Shannon index and Simpson index of soil bacterial community were positively correlated with soil total nitrogen and total potassium(P<0.05).Soil total nitrogen was positively correlated with the sequencing depth index of soil fungal community(P<0.05),and soil moisture content was negatively correlated with the sequencing depth index of soil fungal community(P<0.05).The distribution of Ascomycetes was negatively correlated with soil p H(P<0.05). |
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