Fig. 5Functional versus taxonomic groups of microbiota in the water of river ecosystems. (a) Z-scores achieved by standardization of relative abundances of functional groups (heatmap) within each functional group (heatmap, averaged across each functional group). Rank correlations between environmental variables and relative abundances of functional groups. Blue and red colors indicate negative and positive correlations, respectively. *, P < 0.05; **, P < 0.01; and ***, P < 0.001. (b) Key functions of microbiota under different land-use types.
The functional prediction results showed that the microbial functional groups in sediment samples were more diverse than those in water samples. A comparative analysis across the three river areas revealed numerous microbial function groups associated with N respiration, nitrate respiration, denitrification, and human pathogens in the sediment of Weihe River. In addition, there were multiple microbial function groups associated with fermentation, methanogenesis, aerobic nitrite oxidation, and human pathogenic gastroenteritis in the sediment of Hanjiang River. Furthermore, there were some microbial functional groups associated with aerobic chemoheterotrophy, photoautotrophy, and intracellular parasites in the sediment of Qinling tributaries (Fig. S6).
To determine whether the functional groups with differences in relative abundance could serve as biomarkers of anthropogenic disturbance in freshwater environments, an LEfSe analysis was performed at the functional group level (LDA > 2, P < 0.05). N cycling was the main function in the Weihe River sediment, with denitrification and organic degradation being the main functions in autumn, and ammonification and metal respiration being the main functions in spring (Fig. 6a-b). Fermentation and oxidation-related functions were dominant in the Hanjiang River sediment. Phototrophy and oxidation were the main functions in the sediment of Qinling tributaries. Overall, N metabolism was the primary function in the river areas under different land-use types, and the relative abundance of microbial functional groups associated with N metabolism was significantly higher in the sediment of Weihe River than those in the other areas in autumn (Fig. 6c-d).