Microbial interaction patterns and nitrogen cycling regularities in lake sediments under different trophic conditions.

Exploring how nitrogen (N) cycling microbes interact in eutrophic lake sediments and how biogenic elements influence the nitrogen cycle is crucial for understanding biogeochemical cycles and nitrogen accumulation mechanisms. In this study, sediment samples were collected from various areas of Taihu Lake with different trophic conditions in all four seasons from 2015 to 2017. Using high-throughput sequencing and molecular ecological network analysis, we investigated the microbial interaction patterns and the role of nitrogen cycling in sediments from lakes with different trophic conditions. The results showed distinct structures of sediment microbial networks between lake areas with different trophic conditions. In the more eutrophic region, network indices indicate higher transfer efficiency of energy, material, and information, more significant competition, and weaker niche differentiation of the microbial community. The sedimentary environment in the moderately eutrophic area exhibited greater potential for denitrification, nitrification, and anammox compared to the mesotrophic area, but the inhibition between N functional microbes and limitations in N removal processes were also more likely to occur. The topological structure of the networks showed that the carbon (C), sulfur (S), and iron (Fe) cycles had a strong influence on the nitrogen cycle in both lake areas. In the moderately eutrophic lake area, C- and S-cycling functional bacteria facilitated a closed cycle of the coupled N fixation-nitrification-DNRA (dissimilatory nitrate reduction to ammonium) process and reduced N removal. In the mesotrophic lake area, C- and S-cycling functional bacteria promoted both N fixation and mineralization, and Fe-cycling functional bacteria coupled with denitrifiers enhanced the nitrogen removal process of products from nitrogen fixation and mineralization. This study improved the understanding of the nitrogen cycling mechanism in lake sediments under different trophic conditions.