| The vegetation in the riparian zone plays an important role in maintaining the landscape stability and ecological security of the watershed.Due to the topographic complexity and seasonal changes of river water,the plant communities in the riparian zone show obvious temporal succession and spatial gradient patterns.The succession of the vegetation community and understory soil bacterial community and biodiversity show unique dynamic processes and relationships.Revealing the factors affecting the succession of the plant community,especially the driving mechanism of the composition of the bacterial community and biodiversity,which has important guiding significance for the protection and restoration of ecological functions of the riparian zone,and the improvement of the riparian plant community and understory microhabitat conditions and ecological functions.This study is located in Pangquangou Nature Reserve,Shanxi Province,using space instead of time,8 types riparian plant communities in different succession stages in the upper reaches of the Wenyu River were selected(named after the constructive species,namely Multi-flower meadow,Hippophae shrub,Salix shrub,Poplar forest,Poplar birch forest,Poplar birch and larix forest,Larix picea forest and Picea forest)and understory soil as the research objects,with the relationship and interaction of the composite ecosystem "vegetation-soil-microorganism" as the starting point,the riparian plant community composition and the change characteristics of species diversity were investigated,and the DCA ordination method was used to analyze the succession of the riparian plant community;the physical and chemical properties of the soil were analyzed and determined;the high-throughput sequencing methods were used to analyze the changes in the composition and biodiversity of the soil bacterial and denitrifiers communities;which revealed that the soil physical and chemical properties and other ecological factors play important roles in the succession of plant communities,and the driving and influencing mechanism of the dynamic changes of the microbial community,and the regulation mechanism of coupling and interaction with the understory soil bacterial community in the succession process of the riparian plant community in the upper reaches of the Wenyu River.It provided a scientific theoretical basis for vegetation protection and ecological restoration in the riparian zone of the upper reaches of Wenyu River.The main findings are as follows:1.The sample plots of the 8 types riparian plant communities in the upper reaches of the Wenyu River formed a clear six-stage succession sequence,in order: Montane grassland(Ⅰ),Mountane deciduous broad-leaved shrub(Ⅱ,including Hippophae and Salix shrub),Mountane small and broad-leaved forest(Ⅲ,including Poplar and Poplar birch forest),Montane coniferous and broad-leaved mixed forest(Ⅳ,Poplar birch and larix forest),Mountane coniferous mixed forest(Ⅴ,Larix and Picea forest)and Mountane dark coniferous forest(Ⅵ,Picea forest).2.The plant community composition and species diversity of the riparian zone had changed significantly with the succession process.From the Multi-flower grassland to Hippophae and Salix shrub in the early succession stage,the species diversity of plant communities decreased,to the lowest in the Poplar forest,and increased and reached the highest value in the Poplar birch and larix forest,the Larix picea forest and Picea forest showed a downward trend and then tended to be stable.3.The soil physical and chemical properties and denitrifying enzyme activity of the plant communities in the riparian zone were all affected by the plant community succession procession.The overall change pattern first increased and then decreased and tends to stabilize,and there were significant differences between different succession stages.Among them,pH was the highest in succession stageⅠ(Multi-flower meadow);soil organic carbon was the highest in succession stage Ⅴ(Larix picea forest);soil total nitrogen,nitrate nitrogen content and denitrification enzyme activity was the highest in the succession stageⅡ(Hippophae and Salix shrub),and the soil nitrogen cycle biochemical process was also the strongest.4.During the succession of riparian plant communities,the composition of the soil bacterial community and biodiversity understory forest showed a trend of increasing and then decreasing.The α diversity of the soil bacterial community was higher in stageⅢ(Poplar forest).And is also significantly affected by the depth of the soil.At the same time,the composition of the soil bacterial community and the abundance of dominant bacteria were significantly different among the succession stages,such as: the dominant phyla Proteobacteria,Acidobacteria,Actinobacteria,Chloroflexi,Planctomycetes,Nitrospirae,etc.and the dominant genera Nevskia,Rhodoplanes,Rhodococcus,Bacillus)and Nitrospira.5.Soil denitrifying bacterial community composition and biodiversity also showed a trend of first increasing and then decreasing with the succession of the community.The soil depth also significantly affects the composition of the community and the abundance of dominant bacteria.Among them,Proteobacteria was the most dominant denitrifying flora,accounting for 71.8% of the total;the generus Rhodanobacter,Pseudomonas,Azospirillum,Azoarcus,Azospira,Rubrivivax,Sulfuritalea and other dominant generus had significant differences in relative abundances between different succession stages.6.During the succession process of the plant community in the riparian zone of the upper reaches of the Wenyu River,the above-ground plant community and the understory soil microbial community had a significant correlation and interaction procession.The composition of the soil bacteria and denitrifiers community and the abundance content of dominant bacteria were significantly affected by the aboveground plants.The variation of soil physical and chemical properties were important factors driving the succession of above-ground plant communities and the dynamic changes of understory soil microbial communities. |
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