Physiological response and tolerance of Myriophyllum aquaticum to a wide range of ammonium concentrations
2022
Li, Baozhen | Zhang, Ying | Xian, Yingnan | Luo, Pei | Xiao, Runlin | Wu, Jinshui
Myriophyllum aquaticum (M. aquaticum) can be used in constructed wetlands (CWs) to effectively purify swine wastewater with high-ammonia nitrogen (NH₃–N and NH₄⁺-N) concentrations. However, the understanding of its tolerance mechanism to ammonia nitrogen is limited. The physiological response and tolerance mechanism of M. aquaticum to a wide range of NH₄⁺ concentrations (0–35 mM) were investigated in the present study. The results indicated that M. aquaticum can tolerate NH₄⁺ concentrations of up to 30 mM for 21 days and grow well with high nutrient (N, P) uptake. A suitable concentration of NH₄⁺ for a better growth of M. aquaticum was 0.5–20 mM. The free NH₄⁺ content was no obviously increase at NH₄⁺ concentration below 15 mM, indicated there was no obviously ammonium accumulation. Exogenous NH₄⁺ inhibited K⁺ absorption and improved Ca²⁺ absorption, indicating mineral cation could mediate NH₄⁺ homeostasis under NH₄⁺ stress. Moreover, comparison with those in the control group, the activities of glutamine synthetase (GS), glutamate synthetase (GOGAT) in M. aquaticum increased by 52.7%−115% at 1–20 mM NH₄⁺, and superoxide dismutase (SOD) increased by 29.2–143% at 1–35 mM NH₄⁺. This indicated that the high NH₄⁺ tolerance of M. aquaticum was mainly due to the balance of free NH₄⁺ content in tissues, as well as improved nitrogen metabolism and antioxidant system. This could be attributed to the role of the GS-GOGAT cycle and SOD. In conclusion, M. aquaticum, which tolerates high NH₄⁺ concentration and has a high N uptake ability, can be used as a good candidate specie to help develop more efficient management strategies for treating high-NH₄⁺ wastewater in CW systems.
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