Changes In Structure And Diversity Of Soil Microbial Communities Across The Main Grasslands In Northern China

Since soil bacteria play key roles in many ecological processes, including nutrient cycling and energy flow, the changes of soil bacterial diversity and community structure and their divers have emerged as a major scientific issue today. Most previous studies were conducted at a microcosm research scale, little is known about whether a common set of factors govern soil microbial community structure and diversity when spatial scale varies across microcosm, regional, and global levels. As a consequence, this study sets a research transect in the east part of Eurasian grassland, investigating the changes of soil bacterial community structure and diversity across different grassland types, analyzing the role of soil physicochemical properties played in those changes, which may improve our understanding on the changes of soil bacterial community structure and diversity and their driving forces. In addition, it will reveal how to maximize the ecological function and economic value of grassland from the perspective of nutrient cycling and energy flow, and provide a theoretical basis for grassland protection and maintain.For this study, a transect with five research sites (plain meadow, meadow steppe, typical steppe, desert steppe, and alpine meadow) was established, and the changes of soil bacterial community structure and diversity and their driving forces were analyzed by high-throughput sequencing method. The results are as follows:(1) Soil bacterial genetic diversity in alpine meadow was significantly different from that of plain meadow, meadow steppe, typical steppe and desert steppe. But there was no significant difference of bacterial genetic diversity among those four grassland types. Bacterial diversity exhibited a positive correlation with soil moisture, organic carbon, total nitrogen, and N:P ratio, but a negative correlation with pH value. The RDA result indicates that bacterial diversity was mainly driven by organic carbon.(2) Of the classifiable sequences,39phyla were identified among all the soil samples. According to relative abundance of those phyla, these phyla could be classified into three groups, dominant phyla, common phyla, and rare phyla. Dominant phyla were those which had relatively high abundances in nearly all of the soils examined, including Actinobacteria, Acidbacteria, Alphaprotebacteria and Chloroflexi. Common phyla were those which were less abundant but still were found in most of the soils examined. We defined rare phyla here as those phyla represented by<2%of the sequences, accounting for10%of total sequences.(3) Different grassland types harbor similar composition of dominant and common bacterial phyla but distinct bacterial community structures. Relative abundance of Actinobacteria, Acidbacteria, and Chloroflexi exhibit a negative correlation with soil organic carbon, but relative abundance of Alphapfotebacteria exhibits a positive, correlation with soil organic carbon. Relative abundance of Verrucomicrobia has no significant correlation with soil organic carbon, which was the main driving force of relative abundance of dominant phyla. Relative abundance of Verrucomicrobia exhibits a negative correlation with soil pH value and electronic conductivity.(4) There were significant differences of soil microbial biomass carbon (SMBC) across these grassland types. SMBC ranged from0.14to0.92g·kg-1, and was highest in the typical steppe. Of those soil characteristics considered, SMBC exhibits a negative correlation with soil organic carbon, total nitrogen, C:N ratio, and N:P ratio. Among those soil characteristics, soil C:N ratio was the main driving force.In conclusion, soil microbial biomass carbon, bacterial community structure and diversity were highly distinct across these grassland types at a regional scale. Soil bacterial genetic diversity was mainly driven by soil organic carbon. SMBC was mainly driven by soil C:N ratio. Although dominant phyla share the same main driving force with bacterial genetic diversity, other phyla have different driving forces. This study not only improves our understanding of the change of soil bacterial community at a regional scale, but also provides a theoretical basis for grassland protection.