More Robust Co-Occurrence Patterns and Stronger Dispersal Limitations of Bacterial Communities in Wet than Dry Seasons of Riparian Wetlands

Riparian wetlands comprise microbial communities that are easily affected by the surrounding conditions, especially in agricultural landscapes with a wide range of ecosystem services. After comparing the wet and dry season microbiota, we found that the soil bacterial community of the wet season exhibited a higher complexity and stability of soil bacterial network and stronger dispersal limitations than that of the dry season; however, the dry season bacteria showed stronger homogeneous selection than the wet season bacteria. ABSTRACT Riparian wetlands can be used as “sentinels” of environmental changes and play pivotal roles in ecological and biogeochemical processes. The bacterial community is an essential and rapidly responding component in riparian areas. However, the co-occurrence patterns and phylogenetic group-based ecological processes during wet-dry periods are still open questions. Here, we compared the co-occurrence patterns and phylogenetic group-based assembly mechanisms of soil bacterial communities in typical riparian wetlands across wet and dry seasons, which are subjected to intensive agricultural activities. The results showed that the potential functions, community composition, network structure, and phylogenetic group-based ecological processes of the bacterial community were distinct between the wet and dry seasons. The stability and complexity of the wet season bacterial network were significantly higher than those of the dry season bacterial network. Moreover, the phylogenetic group-based null model analysis showed that homogeneous selection (HoS), dispersal limitation (DL), and drift (DR) were the most important ecological processes for the bacterial community assemblages, with a higher proportion of DL in the wet season (36.7%) than in the dry season (25.5%) but lower contributions of the HoS (36.1% versus 41.3%) and DR (20.8% versus 25.4%). The communities dominated by Flavobacteriales, Burkholderiales, and Sphingomonadales in the wet season were controlled more by dispersal limitation, whereas they were significantly negatively correlated with precipitation, dissolved organic carbon, and total carbon in the dry season, respectively. These findings expand our understanding of the network vulnerability and assembly mechanisms in fragile anthropologically affected riparian wetland ecosystems. IMPORTANCE Riparian wetlands comprise microbial communities that are easily affected by the surrounding conditions, especially in agricultural landscapes with a wide range of ecosystem services. After comparing the wet and dry season microbiota, we found that the soil bacterial community of the wet season exhibited a higher complexity and stability of soil bacterial network and stronger dispersal limitations than that of the dry season; however, the dry season bacteria showed stronger homogeneous selection than the wet season bacteria. The co-occurrence and phylogenetic group-based bacterial community assembly mechanisms were mainly shaped by the divergence in temperature and precipitation between seasons. Revealing the variations in the potential functions, co-occurrence, and community assembly processes between wet and dry seasons is critical to understanding the maintenance of soil microbial diversity in riparian wetlands with regard to environmental sceneries.