Response of soil protists to habitat change in coastal wetlands across southeastern China

The response of protists to habitat change is of great significance for predicting and managing soil ecological functions under human influence. The wetland areas along the southeast coast of China have experienced a transition from mudflats (MFs) to S. alterniflora marshes (SAs) and aquaculture ponds (APs). However, it remains unclear how the changes in coastal wetland habitats affect protistan communities. Here, we studied the effects on protistan diversity, community structure, biogeographic pattern, and assembly process in sediments from 21 coastal wetlands in five provinces of southeast China. The results showed that habitat changes had no significant impact on the alpha diversity of protists, but significantly changed the protistan community structure, and concentrations of salinity and sulfate were the most important environmental factors controlling the diversity and community structure of protists, respectively (P < 0.05). Habitat changes also changed the community composition and functional group structure of protists. Specifically, phototrophs significantly decreased from 19.96% to 11.2% after S. alterniflora invasion, while cercozoan taxa became more dominant in aquaculture ponds. Sediment particle size was an important variable affecting the composition of the consumers and phototrophs communities. Spatial turnover of protistan communities increased following S. alterniflora invasion, as evidenced by steeper distance-decay slopes in S. alterniflora marshes. Deterministic processes shape the protistan community assembly in the three habitats of coastal wetlands, with S. alterniflora marshes showing the strongest deterministic signal. Altogether, our results highlight the critical role of plant invasion and land-use change in driving the distribution of protists in coastal wetlands. These results provide a basis for future coastal wetland restoration and management.