Effects of water quality and bacterial community composition on dissolved organic matter structure in Daihai lake and the mechanisms.

The migration of organic matter in salinized lakes was critical in maintaining ecological balance and material circulation process of inland shallow lakes. To clarify the ecological and microbial mechanism of material transport and transformation, the microbial community structure and the characteristics of dissolved organic matter (DOM) in the sediment of Daihai Lake, a typical saline lake at the Yellow River Basin, were explored with three-dimensional excitation and emission matrix fluorescence (3DEEM), parallel factor analysis (PARAFAC) and 16 S rRNA techniques. The correlation between environmental factors, DOM composition and the bacterial community structure were also studied for identifying the key factors of community formation. DOM in the lake demonstrated both terrigenous and endogenous characteristics. Protein-like materials accounted for 74% of the total fluorescence intensity in the sediment, where 1127 species, 671 genera, 468 families, 157 classes, 317 orders, 59 phyla of microorganisms were detected. Among the top 10 abundant taxa of each level, Firmicutes, Actinobacterota, Acidimicrobiia and Alphaproteobacteria had the greatest influence on the composition and structure of DOM (|R| > 0.7, p < 0.01). Microbial metabolism was a key process of transforming sediment organic matter from terrestrial humic-like to protein-like matter, accounting for 81% of total fluorescence signal in saline lake samples, while salinity, temperature, dissolved oxygen and electrical conductivity also had significant impacts during the process (|R|>0.7, p < 0.05). The research provides fundamental data and enlightenment for the improvement of the saline inland lake environment.