Soil water content and pH drive archaeal distribution patterns in sediment and soils of water-level-fluctuating zones in the East Dongting Lake wetland, China

Archaea play a vital role in Earth's geochemical cycles, but the factors that drive their distribution between sediments and water-level-fluctuating zones in the East Dongting Lake (EDL) wetland are poorly understood. Here, we used Illumina MiSeq to investigate the variation in the soil archaeal community structure and diversity among sediments and four water-level-fluctuating zones (mudflat, sedge, sedge-Phragmites, and Phragmites) in the EDL wetland. Diverse archaeal assemblages were found in our study, Crenarchaeota, Euryarchaeota, and ammonia-oxidizing and methanogenic subset were the dominant groups, and all their abundances shifted from sediment to water-level-fluctuating zones. The principal coordinates analysis and cluster analysis showed that the overall archaeal community structure was separated into two clusters: cluster I contained nine samples from sediment, mudflat, and sedge zones, whereas cluster II contained six samples from sedge-Phragmites and Phragmites zones. Archaeal diversity was significantly highest in sediment and lowest in Phragmites zone soils. The Mantel test showed that the variation in archaeal community structure was significantly positively correlated with soil water content and pH. The relative abundances of Crenarchaeota and Nitrososphaerales decreased with soil water content, while Euryarchaeota and Methanomicrobiales increased with soil water content. The relative abundance of Methanomicrobiales significantly decreased with pH (R-2 = 0.34-0.48). Chao 1, observed operational taxonomic units, Shannon index, and Simpson index all correlated significantly positively with water content (R-2 = 0.40-0.60), while Shannon and Simpson indexes both correlated significantly negatively with pH (R-2 = 0.20-0.37). Our results demonstrated that the variations in the archaeal community structure were markedly driven by soil water content and pH in the EDL wetland. Our findings suggested that archaeal communities shifted among sediment and four water-level-fluctuating zones, highlighting that the spatiotemporal heterogeneity of greenhouse gas flux in small scale should be taken into account for accurate prediction of greenhouse gas emissions in the Dongting Lake area, especially on the background of climate change and human activities.