Characteristics of microbial community composition and its relationship with carbon, nitrogen and sulfur in sediments.

Microorganisms play an important role in the biogeochemical cycles of lacustrine sediments. However, little is known about their vertical responses to sedimentary depths and their contributions to important element cycles such as carbon, nitrogen and sulfur. Here, we investigated the community features of sedimental prokaryotes along with vertical profiles (i.e., sedimental depths of 0-230 cm) in the Dongting watershed. In the entire profile, the bacterial diversity wavelike decreased with increasing sediment depths, whereas archaeal diversity increased monotonically in the deep layer (100-230 cm). Bacteria were more sensitive to sedimental depths than archaea (B: P < 0.001, R = 0.534; A: P < 0.001, R = 0.327). The relative abundance of the primary phylum of bacteria (e.g. Proteobacteria) and archaea (e.g. Thaumarchaeota) changed significantly with sediment layers (P < 0.05). The vertical distribution of prokaryotes in sediments was related to the changes in sediment properties (P < 0.05, e.g., the content of nutrients, pH, texture, etc.). The co-occurrence network analysis further indicated that the superficial (0-40 cm) and deep (100-230 cm) networks contained more tightly connected node groups (more modules number), while the tighter connections (shorter APL) and more complex networks (higher avgK) were seen in sub-deep (40-100 cm) sediments. Based on the FAPROTAX database, we found that the predicted prokaryotic microbial functional groups involved in the N cycle had the highest abundance (87.47%), followed by the C cycle (9.48%) and the S cycle (2.39%). In addition, these groups were enriched in the superficial and deep layers. Taken together, these results reveal a new perspective on the vertical spatial variation in microorganisms at the fine-scale of the lake sediments. Distinct microbiome response patterns may have important implications for carbon, nitrogen and sulfur cycling along with the sediment profile in Dongting lake ecosystems.