Elevation Patterns And Community Assembly Of Soil Bacteria On The Mount Gangbala In Tibet,China

Revealing the altitudinal distribution pattern of soil bacterial community in mountainous areas can deepen the understanding of the relationship between soil bacterial community structure and its influencing factors along the environmental gradient in the mountain ecosystem,and which has important scientific significance for the protection,planning and utilization of mountain microbial diversity resources.However,at present,the research on the relationship between the distribution pattern of soil bacterial community diversity and environmental factors at a fine scale of the Qinghai-Tibet Plateau is rarely involved.In order to understand the distribution pattern and community construction mechanism of mountain soil bacterial community along the altitude,in this study,one altitude transect was set up every 100 m vertical height between 3800 m and 4900 m on the southern slope of Mount Gangbala in September 2020,for a total of 12 altitude transects,and 6 replicate plots were set up at each altitude,for a total of 72 soil samples,by measuring soil physicochemical properties and enzyme activities,extracting soil bacterial DNA and performing highthroughput sequencing,the structure,diversity and community construction mechanism of soil bacterial community on Mount Gangbala and its relationship with soil physicochemical factors and enzyme activities were studied.The main conclusions are as follows:(1)The coastal pulling gradient of soil physicochemical properties of Mount Gangbala showed different trends,the contents of soil organic carbon,total nitrogen,alkaline hydrolyzable nitrogen and total phosphorus increased significantly with the increase of altitude,soil available phosphorus and p H decreased significantly with the increase of altitude,there was no obvious trend of soil carbon and nitrogen ratio in Mount Gangbala compared with coastal pulling gradient,and the change of soil physical and chemical properties was mainly affected by soil enzyme activity,vegetation type and soil microbial community caused by altitude change.(2)There was no significant trend of soil enzyme activity with altitude,and the activity of chitin synthetase was the highest among soil enzymes,followed by neutral phosphatase,β-D-glucosidase,polyphenol oxidase and acidic protease.Alkaline protease has the lowest activity.There was a significant correlation between the soil physicochemical properties and soil enzyme activities on Mount Gangbala,and the altitude was significantly negatively correlated with chitinase and β-Nacetylglucosadase,and positively correlated with acid protease and neutral phosphatase.(3)The soil bacterial community of Mount Gangbala includes 36 phyla,125 classes,307 orders,477 families,838 genera,1878 species,and8914 OTUs,and the richness of soil bacterial communities showed a distribution trend of first increasing and then decreasing with altitude,and the specific coastal gradient of soil bacterial communities showed an inverted U-shaped pattern.The dominant phyla of the soil bacterial community in the Mount Gangbala are Actinobacteriota,Proteobacteria,Acidobacteriota,Chloroflexi,Verrucomicrobiota,Gemmatimonadota,etc.The relative abundance of Actinobacteriota,Gemmatimonadota,Myxococcota and Bacteroidota decreased significantly with altitude,and the relative abundance of Verrucomicrobiota and Methylomirabilota increased significantly with altitude,and altitude had a significant effect on the composition of soil bacterial communities on Mount Gangbala.(4)The Alpha diversity of soil bacterial communities on Mount Gangbala decreased gradually with altitude,and the Shannon index value of soil bacterial communities decreased significantly with altitude.The Simpson index of soil bacterial community increased significantly with altitude.The Ace index value of soil bacterial community showed a unimodal trend with the increase of altitude.The value of Chao index of soil bacterial community showed a unimodal trend with the increase of altitude.There were significant differences in the coastal pulling gradient of soil bacterial community beta diversity on Mount Gangbala,and the altitude had a significant effect on the soil bacterial diversity and community structure differences on Mount Gangbala,and the intra-group differences of soil bacterial communities in different altitude groups were smaller than the differences between groups.(5)Soil physicochemical factors are the key environmental factors affecting the characteristics of soil bacterial community on Mount Gangbala,and soil enzyme activity has a certain influence on soil bacterial community composition.p H was the environmental factor with the greatest impact on soil bacterial communities,followed by alkaline hydrolyzable nitrogen,total nitrogen,available phosphorus,total phosphorus,organic carbon and carbon-nitrogen ratio.p H and available phosphorus were positively correlated with soil bacterial community diversity,and alkaline hydrolyzable nitrogen,total nitrogen,total phosphorus,organic carbon and carbon-nitrogen ratios were negatively correlated with soil bacterial community diversity.Soil neutral phosphatase,neutral protease,acid protease,chitinase,β-N-acetylglucosadase and peroxidase had significant effects on the dominant bacterial phyla,chitinase,peroxidase and β-Nacetylglucosamine were positively correlated with soil bacterial community diversity,and neutral phosphatase,neutral protease,acid protease were negatively correlated with soil bacterial community diversity.(6)The mechanism of soil bacterial community construction on Mount Gangbala is dominated by the random process,and deterministic factors also play an important role in the community construction process.The coastal pulling gradient of soil bacterial community showed significant characteristics of distance attenuation,and soil physicochemical factors had a significant influence on the structure dynamics of soil bacterial community.