The response of microbial communities to environmental factors in bank soil and river sediment: A case study along the mainstream of the Yangtze River.

Microbial communities, which are crucial for ecosystem function and sustainability, are under environmental pressure. Using phospholipid fatty acids (PLFAs) as a measure of microbial biomass and community structure, the responses of microorganisms to environmental drivers were studied in bank soil and sediment alongside the Yangtze River in China. Thirty-eight sites were investigated over a length of 5500 km, ranging from the plateau to the estuary. Redundancy analysis revealed that microbial community composition in the bank soil was affected by MP (7.8%), geography (19.2%), and physicochemical properties (23.1%), while in the sediment, relevant factors were MP additives (12.8%), metals (21.1%), and physicochemical properties (23.3%). Variations in climate conditions along the course of the river had no effect on the microbial communities in the two habitats. Linear discriminant analysis of the PLFAs profiles showed changes in microbial community composition due to land use (forest, grass, cropland and built land), site class (up-, mid- and downstream) and MPs pollution level in both bank soil and sediment. The increased Gram-positive to negative bacteria (g+/g-) ratio and decreased iso-to anteiso-fatty acid (i/a) ratio indicated greater stress, such as caused by MP pollution (g+/g-: 12.6 to 19.3; i/a: 1.9 to 1.6). In bank soil, total microbial biomass was influenced by urbanization rate and nutrient availability. Specifically, total carbon (TC), total phosphorus (TP), and ammonium nitrogen (NH-N) had a positive impact, while inorganic phosphorus (IP), total potassium (TK) and nitrate nitrogen (NO-N) had a negative impact. In contrast, in sediment only TC had a negative effect on biomass. This study applied PLFA to explore microbial communities and structures responses to environmental drivers in riverine habitats, revealing that anthropogenic factors (e.g. MP pollution and nutrient enrichment) alter microbial communities with urbanization.