Tolerance and physiological responses of sweet flag (Acorus calamus L.) under nitrite stress during wastewater treatment

Various newly discovered novel biological nitrogen removal (BNR) routes via nitrite offer great potential for improving nitrogen removal efficiency of constructed wetlands. In these novel routes, nitrite is required as the substrate or intermediary media. Hence, in the present study, the tolerance and physiological responses of sweet flag (Acorus calamus L.) to nitrite stress were investigated. Results showed that the physiology of sweet flag was not significantly affected when exposed to nitrite up to 20 mg/L. High nitrite levels (≥30 mg/L) led to changes in its cell membrane permeability, plant photosynthesis and activities of antioxidant enzymes. Particularly, when exposed to a nitrite level of 40 mg/L, sweet flag displayed trends of significant increase in the percentage of electrolyte leakage and contents of malondialdehyde and proline, whereas the chlorophyll content and plant height decreased and antioxidant defence systems were disrupted. Therefore, for CWs with sweet flag, 30 mg/L is the recommended threshold value for nitrite.