Benthic bacterial communities and bacteria–environment interactions after Kandelia obovata introduction and Spartina alterniflora invasion in Yueqing Bay, China

Kandelia obovata and Spartina alterniflora can significantly affect sediment properties and benthic bacterial communities. However, little is known about the different impacts of K. obovata introduction and S. alterniflora invasion on local ecosystems. In this study, sediment properties and bacterial communities were determined at different depths (0–30, 30–60, 60–90 cm) in mudflat, K. obovata and S. alterniflora habitats in Yueqing Bay, Zhejiang Province, China. The results showed that K. obovata sediments had higher soil organic carbon contents and exhibited higher heavy metals, of which Cu posed a moderate contamination according to the geoaccumulation index. K. obovata habitats also presented more distinct bacterial communities, with Gemmatimonadetes abundant and acting as keystone connectors. The shift in bacterial communities after K. obovata introduction was mainly caused by changes in sediment organic carbon, Cd and Zn concentrations. S. alterniflora habitats had higher proportions of Anaerolineae and Sulfurovum and some bacteria that are beneficial to plant growth, including Cyanobacteria and Erythrobacter. Bacteria–environment interactions showed that heavy metals formed a more complex and closer co-occurrence network with Proteobacteria and Gemmatimonadetes after K. obovata introduction, while S. alterniflora invasion simplified sediment bacterial co-occurrence networks and bacteria–environment interactions in native ecosystems. Our results revealed that the impacts of S. alterniflora invasion on local ecosystems were outweighed by K. obovata introduction in Yueqing Bay. The present study could improve the understanding of ecological changes after K. obovata introduction and S. alterniflora invasion.