Abstract
Urbanization-induced environmental changes are becoming a major threat to river systems. However, little is known about how urbanization affects aquatic microbial communities despite their critical role in maintaining ecological processes and nutrient cycling. Here, we investigated assembly processes of habitat generalists and specialists in different urbanization stages of subtropical rivers. The results highlight that nitrogen compounds can influence the composition of the microbial community. Proteobacteria and Bacteroidetes, as well as Cyanobacteria were identified as dominant phyla in urbanization rivers. Both total diversity and total species richness of generalists were significantly higher than that of specialists, while beta diversity of generalists was significantly higher in low-level urbanization rivers (LUS) than that in high-level urbanization river (HUS). For the generalist, heterogeneous selection is the most important process for the assembly of HUS in winter, but dispersal limitation, drift and other nondominated processes were mainly the dominant assembly process for the establishment of LUS whether in summer or winter. Similarly, stochastic processes were the main assembly of specialists for LUS and HUS, whether in summer or winter. In summer HUS and winter LUS, a more complex network was found in the generalists and specialists, while a significantly stronger network was found in the complexity and robustness of the co-occurrence network compared to HUS. Overall, these suggest that the specialists and nitrogen play a key role in shaping urbanization-induced homogenization of microbial communities. The insights gained from this study may be helpful in understanding how urbanization affects microbial communities and their ecological assembly mechanisms.