Biogeographical distribution of bacterial communities in saline agricultural soil

Abstract Saline soils suppress plant growth and reduce yield worldwide, thereby pose a serious threat to agriculture. Although microbes drive major biogeochemical cycles and play an integral role in agricultural production, understanding of the microbial distribution patterns in saline agricultural systems remains limited. Here we investigated the co-occurrence and biogeographical patterns of bacterial communities in saline agricultural soils at a regional scale in north-west China. Our results revealed a trend towards increasing bacterial abundance at higher longitudes. By contrast, bacterial diversity exhibited different spatial patterns and declined with increasing salinity. Bacteroidetes, Gammaproteobacteria, Alphaproteobacteria and Gemmatimonadetes were the dominant groups across all soil samples (>5% of all sequences). Additionally, members belonging to Flavobacteriaceae, Cytophagaceae, Halomonadaceae, Acidobacteria and Gemmatimonadetes were identified as indicators across the salinity gradient. Salinity levels also affected the modularity of bacterial co-occurrence networks, with module composition differing between soil salinity levels. Bacteria belonging to Acidobacteria subgroup 4, Acidobacteria subgroup 6, Gemmatimonadetes and Rhodospirillales were statistically identified as the keystone taxa. Geographical distance explained 5.08% of the community variation, whereas soil parameters explained 27.26% variation, with salinity as a major driver explaining 15.18% of the variation. Therefore, bacterial communities were geographically distributed along the longitude gradient, and soil salinity was more important than geographical isolation in shaping soil bacterial communities. Taken together, our results indicate that salinity alters bacterial network modularity and drives spatial distribution in saline agricultural soils.