ABSTRACT
Elevation gradients could provide natural experiments to examine geomorphological influences on biota ecology and evolution, however little is known about microbial community structures with soil depths along altitudinal gradients in karst graben basin of Yunnan-Kweichow Plateau. Here, bulk soil in A layer (0 ~ 10 cm) and B layer (10 ~ 20 cm) from two transect Mounts were analyzed by using high-throughput sequencing coupled with physicochemical analysis. It was found that the top five phyla in A layer were Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Verrucomicrobia, and the top five phyla in B layer were Proteobacteria, Acidobacteria, Actinobacteria, Verrucomicrobia, and Chloroflexi in a near-neutral environment. Edaphic parameters were different in two layers along altitudinal gradients. Besides that, soil microbial community compositions varied along altitudinal gradient, and soil organic carbon (SOC) and total nitrogen (TN) increased monotonically with increasing elevation. It was further observed that Shannon indexes with increasing altitudes in two transect Mounts decreased monotonically with significant difference (p = 0.001), however beta diversity followed U-trend with significant difference (p = 0.001). The low proportions of unique operational taxonomic units (OTUs) appeared at high altitude areas which impact the widely accepted elevation Rapoport's rules. The dominant Bradyrhizobium (alphaproteobacterial OTU 1) identified at high altitudes in two layers constitutes the important group of free-living diazotrophs and could bring fixed N into soils, which simultaneously enhances SOC and TN accumulation at high altitudes (p < 0.01). Due to different responses of bacterial community to environmental changes varying with soil depths, altitudinal gradients exerted negative effects on soil bacterial communities via soil physical properties and positive effects on soil bacterial diversities via soil chemical properties in A layer, however the results in B layer were opposite. Overall, our study is the first attempt to bring a deeper understanding of soil microbial structure patterns along altitudinal gradients at karst graben basin areas.
ABSTRACT
In order to explore the effect of land-use change on soil bacteria in wetland systems, the topsoil (0-20 cm) of a natural wetland (NW), paddy field (PF), and dry land (DL) were collected in the Huixian karst wetland. The α-diversity, species composition, and abundance of soil bacterial communities were analyzed using high-throughput sequencing. The effect of environmental factors on bacterial community structure was also examined. The results showed that the soil bacteria in the Huixian karst wetland can be divided into 49 phyla and 145 classes. The Shannon index of bacteria in the PF was significantly higher, and the Simpson index of bacteria in the NW is significantly lower, than in the other two land-use types. The dominant phyla (operational taxonomic units, OTUs>1%) in the NW were Proteobacteria (52.15%), Actinobacteria (15.16%), and Acidobacteria (8.80%); the dominant phyla in the PF were Proteobacteria (45.79%), Acidobacteria (17.20%), and Chloroflexi (11.75%); the dominant phyla in the DL were Proteus (51.42%), Acidobacteria (15.51%), and Chloroflexi (7.43%). The dominant classes (OTUs>1%) in the NW were α-Proteobacteria (17.98%), ß-Proteobacteria (13.72%), and Actinobacteria (13.13%); the dominant classes in the PF were Acidobacteria (14.35%), ß-Proteobacteria (13.37%), and δ-Proteobacteria (12.02%); the dominant classes in the DL were α-Proteobacteria (19.44%), Formobacteria (13.30%), and Acidobacteria (13.03%). Among the dominant OTUs (>0.3%), the dominant genera of in the NW were Sphingomonas (OTU2, 59), Micromonospora (OTU5, 24 and 50487), Gemmatimonas (OTU1), and Tenotrophomonas (OTU8); the dominant genera in the PF were Lysobacter (OTU4 and 115) and Aquabacterium (OTU33); the dominant genera in the DL were Sphingomonas (OTU85, 157 and 2916), Rhodanobacter (OTU19 and 52), and Penlobacterium (OTU60). A heatmap showed that there were significant differences in soil bacterial community structure among the three land-use types. Redundancy analysis showed that pH, soil organic carbon (SOC), total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), exchangeable Mg2+, exchangeable Ca2+, soluble organic carbon (DOC), and available phosphorus (AP) were the main factors that affected the bacterial community structure in the Huixian karst wetland. These results indicate that changes in land-use types have significantly shaped the structure of soil bacterial communities in this area.