Effect of plant development on phosphorus fractions and microbial phosphorus cycle in subsurface flow constructed wetlands

Plant development can influence the effluent concentrations of total phosphorus (TP) in constructed wetlands (CWs). However, little is known regarding the effect of plant development on P cycling in CWs. In this study, Juncus effusus was selected as wetland plant. The P removal efficiency, the change of P fractions in substrate and the relative abundance of P cycling genes were investigated along with plant development in CWs over seedling, mature, and wilting stages. The results showed that the effluent concentration of TP in CWs varied towards higher levels along with the plant development, and significant differences from the previous two stages were observed at the wilting stage. P fractions in the substrate accumulated with continuing influent, providing conditions for P cycling. There were differences in the relative abundance of functional genes involved in P cycling at different stages of plant development. With plant development, microbial transportation of P (indicated by the genes of phnCDE and ugpABCE) was weakened and then enhanced, while in contrast inorganic P solubilization (indicated by the genes of gcd) and organic P mineralization (indicated by the genes of phnP and phnW) were enhanced and then weakened. Pearson correlation analysis results indicated that the P cycling in the substrate of CWs was enriched with plant development, which promoted labile P accumulation in the CW substrate, resulting in higher effluent TP concentration at the wilting stage. Plant development was found to influence P cycling related microbes by regulating the relative abundance of genes involved in P cycling. The acquired results provided new insights into the effect of plant development on P cycling and effluent TP concentration stabilization in CWs.