Improving the efficacy of different life-form macrophytes in phytoremediation of artificial eutrophic water by combined planting

Phytoremediation of the eutrophic water bodies by using various macrophytes has long been considered effective and economical. However, the understanding of combining macrophytes to maximize efficacy in the restoration is still limited. In this study, three different life-form macrophytes were employed to explore the optimal plant combination of eutrophic water purification, including Pontederia cordata L . (E: emergent), Pistia stratiotes L. (F: floating), and Hydrilla verticillata (L. f.) Royle (S: submerged). The effects on water quality, removal of the excess nutrients (TN, NH 3 -N, NO 3 -N, and TP) in the water, along with the growth response and the nutrient accumulation of the macrophytes were investigated both individually and in combination. The phytoremediation of every single macrophyte was significantly improved by combined planting and increasing the diversity of the combination led to better enhancements. In general, the treatment with macrophytes in three life forms (EFS) not only resulted in the highest removal rates of the TN, NH 3 -N, NO 3 -N, and TP (40.89, 33.50, 46.81, and 43.55%, respectively) but also decreased the turbidity and increased the dissolved oxygen more effectively and efficiently. Furthermore, EFS mitigated the environmental stress of plants and promoted the accumulation of TN and TP in them, especially the emergent macrophyte P. cordata. The combinations with macrophyte in two life forms (EF, ES, and FS) also exhibited unique strengths: the removal efficacy of TN (39.25%) and TP (46.16%) in FS, and NO 3 -N in EF (48.54%) and ES (49.90%) were also at the forefront; the biomass and nutrient content of the submerged macrophyte H. verticillata in ES were the highest. Moreover, a strong correlation between the eutrophic factors and the plant physiological indexes was observed. These findings highlighted the role of combined planting in phytoremediation and provided a valuable reference for the development of ecological restoration for eutrophic ecosystems.