The influence of Hydraulic loading on Eukaryotic community in surface flow constructed wetlands

Hydraulic loading rate (HLR) may result in significant changes of microbial community in constructed wetlands (CWs), with implications for ecosystem processes. However, information about the effects of HLR change on CW microeukaryotic community traits remians rare. This study used 18S rRNA gene amplicon sequencing to unveil the CW microeukaryotic community traits under two HLRs after one year operation. Results showed that the alpha and beta diversity of microeukaryotic community was significantly different between two CWs. And the alpha diversity and niche breadth index gradually decreased from the inlet to outlet of CW under low HLR (L-CW), while the one with high HLR (H-CW) showed opposite trend. Interestingly, alpha diversity and niche breadth index of L-CW were higher than H-CW. Nucletmycea, Rhizaria, Alveolate, and Stramenopiles accounted for most of the CW microeukaryotic community, while the relative abundances of Stramenopiles, Tubulinea, and Rigifilida were significantly higher in H-CW than in L-CW. EC, AFe and DYN, AP are the primary regulators of microeukaryotic communities in H-CW and L-CW, respectively. Co-occurrence network analysis showed the edges, nodes and average degree of L-CW are higher than H-CW, indicating that L-CW formed a more tightened microbial interaction network than H-CW for a better nutrient cycling. In addition, stochastic processes were relatively more important in constraining the H-CW microeukaryotic assembly than L-CW. Our findings show that HLR could be used as a control parameter to regulate the CW microeukaryotic community, which has certain guiding significance for the CW regulation in the future.