Spatial Distribution Of Soil Microbial Community Structure And Soil Physicochemical Properties In Lijiang Riparian Zone

To implement the ecological restoration project in Lijiang riparian zone,it is necessary to full evaluate the status of soil quality in different regions of typical riparian zone,follow the spatial distribution law of natural soil ecosystem,and design rehabilitation scheme according to local conditions.In this study,soil physicochemical properties,enzyme activities,microorganism quantity,bacterial diversity,and dominant microflora in different spatial regions of Lijiang riparian zone were determined to evaluate the soil quality of riparian zone comprehensively.A total of 120 soil sample plots were set up under 4 kinds of hydrological environmental gradients(gravel zone,grass zone,shrub-grass zone and arbor zone)at 10 research sites in different regions of the Lijiang riparian zones(upper reaches,middle reaches and down reaches).The spatial distribution characteristics and variation mechanism of soils in the riparian zone were discussed by measuring the soil indicators and analying the correlation among these indicators.It provides relevant suggestions for the ecological restoration design of Lijiang riparian zone and theoretical basis for the restoration and reconstruction of degraded riparian ecosystem.The main research results are as follows:(1)The spatial distribution of soil physicochemical properties,soil enzymes and microorganisms in the riparian zone of Lijiang River were significant differences.Horizontally(vertical to the flow direction),with the decrease of flooding frequency,the soil pH value,available nitrogen,available phosphorus and available potassium were all increased firstly and then decreased.The maximum values of soil properties were mostly in the shrub-grass zone and grass zone,and the minimum values were mostly in the gravel zone.The number of microorganisms and soil enzymes also showed similar changes.The results showed that moderate river water disturbance was beneficial to the soil structure and nutrient accumulation in the riparian zone of the Lijiang River,and also contributes to the amounts of microorganisms and enzyme activities,and periodic flooding of river water had a significant effect on soil nutrients in gravel zone.Vertically(along the direction of flow),the sand content was higher in the down reaches of the riparian zone,while the contents of available N,P and K were lower;the number of microoganisms were significantly different in different regions of riparian zones.It shows that the disturbance of human tourism activities or different types of land use will have significant effects on the soil physicochemical properties and microbial quantity in the riparian zone of Lijiang River(2)The spatial distribution of soil microbial community structure in the riparian zone of Lijiang was also significantly different.A total of 76 phyla were detected in the soils of Lijiang riparian zone,and most of them could be assigned to the domain bacteria.among them,Proteobacteria was the predominant phylum in all soils,followed by Acidobacteria,Crenarchaeota,Verrucomicrobia,Planctomycetes,Bacteroidetes et al.Horizontally,with the decrease of flooding frequency,the relative abundance of Proteobacteria decreased gradually,while the relative abundance of Planctomycetes and Acidobacteria increased gradually;soil sand content,pH value and available nitrogen content were significantly correlated with the abundances of major dominant bacteria;the gravel zone,grass zone and shrub-grass zone had higher bacterial diversity but no significant difference between them,the lowest bacterial diversity was in arbor zone.Vertically,the soil bacterial diversity and the relative abundances of dominant bacteria in riparian zones of different regions have no obvious change rule;which indicates that the soil microbial ecosystem in the riparian zone of Lijiang River has stability,resistance and resilience to external disturbances to a certain extent,and the influence of the variation of soil physicochemical properties on microbial diversity is relatively weak in the vertical(3)The spatial variability of soil physical and chemical indices,soil enzymes and microbial communities in the riparian zone of the Lijiang River had a strong consistency on the whole,and there was a strong correlation or mutual exclusion among these indices.Soil sand,pH value and soil organic matter in the riparian zone of Lijiang significantly affected the number of microorganisms;soil sand,pH value,available nitrogen and available phosphorus significantly affected soil enzyme activities;soil sand,pH value and soil water content significantly affected bacterial diversity and relative abundance of dominant bacteria.In the design of ecological restoration of Lijiang riparian zone,it is necessary to follow the gradual changing structure of riparian soil ecosystem,maintain the integrity and complexity of the riparian hydrological environmental gradient,and enhance the service function of soil ecosystem At the same time,it is necessary to design different restoration schemes for different regions.Horizontally,gravel zone is sensitive to soil degradation,and the characteristics of river water periodic disturbance should be fully considered.Vertically,down reaches riparian zone is the key restoration area,and the impacts of human tourism activities and different land use patterns on soil quality should be fully considered.