Succession of bacterial community and methanotrophy during lake shrinkage

Purpose The shrinkage of vast inland lakes affects microbially mediated soil biogeochemical processes, which are critical for maintaining ecosystem sustainability, such as microbial diversity and a balanced CH4 budget. Here we aimed to elucidate shifts in the bacterial community and methanotrophy during the shrinkage of a saline lake. Materials and methods Sediments and soils along a gradient transecting a saline lake, saline riparian land, and grassland were collected. The succession of microbial communities was characterized by high-throughput sequencing of the V4-V5 region of 16S rRNA genes coupled to non-metric multidimensional scaling (NMDS), linear discriminant effect size (LEfSe), community assembly, and co-occurrence network analyses. We further incubated these samples under a 10% CH4 (v/v) atmospheric condition to determine the response of methane oxidation potentials and of methanotrophs to lake shrinkage by using pmoA-based qPCR and amplicon sequencing. Results and discussion LEfSe and NMDS analyses showed significant differences in bacterial communities among 3 stages of lake shrinkage. The microbial taxa with the highest increase were phylogenetically affiliated with unclassified Rhizobiales, Panacagrimonas, and Pseudomonas in saline and grassland soils when compared with sediments. Microbial community assembly was largely determined by deterministic rather than stochastic processes (NTI > 2). The drastic increase of Methylocystis-like (type II) methanotrophs was observed during lake shrinkage, while type I methanotrophs showed a decreasing trend. However, upon consuming high-concentration methane of about 10%, type I methanotrophs dominated methane-oxidizing communities in lake sediment (Methylomonas), riparian saline soil (Methylomicrobium), and grassland soil (Methylobacter). Structural equation model identified soil pH, C/N ratio, and soil texture as key factors affecting methane oxidation rates and the methanotrophic community. Conclusions Lake shrinkage showed profound impacts on the overall bacterial communities and methane oxidizers. Soil physico-chemical properties likely shaped the bacterial community and phylogenetically distinct methanotrophs during lake shrinkage.