Study On Planktonic And Sedimentary Microbial Community Structure And Molecular Ecological Network In The Weihe River Mainstem And Its Typical Tributaries From The Northern Foot Of The Qinling Mountains

The Weihe River Basin is the core of the "The Belt and Road Initiative",Among them,the sediment-laden Weihe River and the water conservation area in the northern foot of the Qinling Mountains are of great significance in maintaining aquatic ecological balance and stability in the arid,semi-arid areas of the Loess Plateau in China and the middle and lower reaches of the Yellow River.Planktonic and sedimentary microorganisms have large biomass and rich species.They are maintainers of river ecosystem structure and functional diversity and important participants in ecological processes.The number of species and abundance reflect the quantity characteristics of communities and the interactions among them reflected by the co-occurrence network are closely related to the ecological status of the river.In the context of watershed ecology research,research on the microbial community structure,driving mechanism and ecological patterns in watershed water ecosystems,especially highly environmentally heterogeneous river ecosystems,will provide an deep understanding of the ecological function,and important data support for evolutionary laws of the life-earth collaboration.In this study,the entire Weihe mainstem and the five typical tributaries originating from the northern foot of the Qinling Mountains were taken as the research obuects.Two systematic surveys of water environment,planktonic and sedimentary microbial communities were carried out from October to November 2017 and April to May 2018.Based on high-throughput sequencing Hiseq platform,advanced bioinformatics analysis method QIIME2,microbial composition and abundance statistics,diversity analysis,and molecular ecological network construction,the structural characteristics and ecological patterns of plankton and sedimentary microbial communities in the mainstem and tributaries were analyzed for a detailed and systematic understanding.The main conclusions drawn are as follows:(1)In terms of taxonomic composition,the difference of the dominant genera composition of planktonic and sedimentary microbial communities and the keystone taxa in the ecological network between the Weihe River mainstem and its tributaries was mainly reflected in the genus that extensively participate in the degradation of organic pollutants(mainstem)and the genus that participate in the degradation of heavy metals(tributaries).Water temperature,conductivity,and total phosphorus were the common major environmental factors structuring the planktonic microbial community in the mainstem and tributaries.Conductivity and ammonium-nitrogen were the common environmental factors affecting the community sedimentary microbial community composition.Chlorophyll a had a significant effect on the composition of planktonic and sedimentary microbial communities in the mainstem.Turbidity,ammonia nitrogen,water temperature and total phosphorus had significant effects on planktonic and sedimentary microbes in tributaries,respectively(2)In terms of functional composition,differences in the functional groups of planktonic and sedimentary microbial communities in the Weihe River mainstem and its tributaries were mainly reflected in the light-dependent groups and nitrogen metabolism groups.The changes of abundance of the two groups had a good coupling with environmental background values(3)In terms of diversity,the average level of planktonic and sedimentary microbial community diversity in the Weihe River mainstem was generally higher than that in the tributaries,and the Faith pd index of planktonic microbial communities in the mainstem was significantly higher than that in the tributaries,which was significantly related to high turbidity conditions.(4)In terms of molecular ecological network,planktonic and sedimentary microbial taxa of the turbid Weihe River mainstem had significant non-random distribution patterns.But the association network was not as tight and complex as the clear streams in the Qinling Mountains In addition,the network correlation type(mainly co-presence or mutual exclusion)of planktonic and sedimentary microorganisms between the mainstem and tributaries was different These indicated that the available resources of microorganisms,the non-randomness of distribution,and the complexity of the ecological network was significantly different between turbid river system and clear river system.Although the environmental pressure of high sediment concentration brings higher microbial diversity,its impact on water quality(dominant species and key species)and aquatic ecological functions(functional groups,ecological networks)cannot be ignored.