Influence of plants on anammox process in constructed Wetland: Irrelevance, inhibition or enhancement

Anaerobic ammonia oxidation (anammox) can become the dominant process of nitrogen removal in constructed wetland, yet whether plants that are signature composition of wetland play a significant role in this process is still unknown. Therefore, this study investigated the influence of plants (Phragmites) on the anammox-driven wetlands by comparing the differences between plant group and non-plant group. The results indicated that the proportion range of anammox process in nitrogen metabolism of both groups was estimated to be 45 %-63 % according to the detected abundance of functional genes, and there was a significant positive relationship between anammox proportion and total nitrogen removal efficiency (R = 0.81, P < 0.05), which confirmed anammox process dominating the nitrogen transformation in all systems. The average total nitrogen removal efficiencies in the systems with plants addition (84-85 %) were significantly superior than those in the corresponding control systems (74-82 %), respectively (P < 0.05). The presence of plants significantly contributed to the increase in the anammox proportion of nitrogen metabolism and the total absolute abundances of anammox bacteria (P < 0.05). Partial Least Squares Path Analysis Model (PLSPM) furtherly revealed that the estimated weight coefficients of plants to anammox process (R = 1.24) showed the larger level than denitrification process (R = 0.25). Overall, plants played an enhancing role in the anammox process of anammox-driven wetlands, rather than irrelevant or potential inhibiting role. The reason was mainly related to the plant role for improving biofilm formation by extracellular polymeric substances (EPS), and a significant positive relationship between EPS concentrations (7-224 mu g.g(-1)) and anammox bacteria abundances (1.63-7.66 x 10(8) cells.g(-1)) was found (R = 0.44, P < 0.05). Besides, the subsidiary reasons also lie in the minimal role of plant roots under higher nitrogen loading and the appropriate nitrogen component of wastewater.

Automated summary

This study found that plants (Phragmites) play a significant role in the anammox-driven wetlands, enhancing the nitrogen transformation. The proportion of anammox process in nitrogen metabolism was estimated to be 45-63% in plant groups. The presence of plants significantly increased the total nitrogen removal efficiency and the abundance of anammox bacteria.