Removal of Nitrogen by Three Plant Species in Hydroponic Culture: Plant Uptake and Microbial Degradation

Three macrophyte species, Typha augustifolia (T. augustifolia), Phragmites australis (P. australis), and Acorus calamus L. (A. calamus L.), have been grown in hydroponic cultivation systems fed with synthetic wastewater. The experiment was designed as 3 × 2 factorial, with three species and two ratios of NH4+/NO3− so as to investigate the nitrogen transformation and nitrogen removal capacity of each species. The nitrogen removal mechanism was further disclosed by comparing biomass production, nitrogen mass balance, and root exudates of the three plant species under different NH4+/NO3− ratios. The results indicated there exists a linear relationship, with positive significance (r = 0.946, p < 0.05), between plant biomass and total nitrogen (TN) removal efficiency; in other words, biomass could best reflect plant ability to remove nitrogen. It is also found that NH4+/NO3− ratio could influence plant biomass and root exudates significantly. Additionally, the hydrogen donor and source of energy in denitrification happened in this research were mainly organic acids and soluble sugars, accounting for approximately 50 % of the composition in root exudates.