Is companionship preferable to being alone? Properly paired wetland plant species improve nutrient phytoremediation outcomes

Understanding the specific nutrient and biomass allocation strategies of wetland plants is crucial for selecting suitable species or combinations of species for wetland restoration or creation. To investigate differences in growth and nutrient uptake, we measured the above- and belowground biomass of 520 individuals from four species grown in single and paired mesocosms over three growing seasons. Key growth parameters—including biomass, maximum height, number of leaves, and culms—were recorded, along with tissue nutrient content (C, N, P, K, Mg, Ca, S, B, Cu, Fe, Mn, Zn) and analyzed using inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Juncus effusus in single-species cultures produced a higher average aboveground biomass and culm production than in paired cultures, where this species increased its own Ca, Mg, Cu, and Mn uptake. Species paired with J. effusus exhibited higher total and aboveground biomass, maximum height, and culm production (Typha latifolia); aboveground biomass and culm production (Phragmites australis); and culm production (Schoenoplectus tabernaemontani) than they did when grown alone. Additionally, S. tabernaemontani paired with J. effusus demonstrated higher nutrient uptake, while P. australis in paired culture enhanced its carbon concentration in aboveground tissues. We also observed strong correlations among nutrient concentrations, particularly in the case of P. australis. These findings highlight the importance of species selection in wetland restoration and creation, as specific species interactions, especially involving J. effusus, can enhance biomass production and nutrient uptake. This research offers valuable insights for optimizing plant pairings to improve nutrient mitigation, which could support the development of advanced ecological modeling for wetlands.