Nitrogen removal performance and mechanism in constructed wetlands under saline conditions: Role of Canna indica inoculated with Piriformospora indica.

The phytopromotional root endophytic fungus Piriformospora indica was introduced into the wetland plant Canna indica L. to explore its impact on nitrogen (N) removal in constructed wetlands (CWs) to treat normal and saline (0.9 % NaCl) wastewater. P. indica colonization increased total nitrogen, NH-N, and NO-N removal efficiencies under normal and saline conditions, with NO-N removal rates significantly increasing by 17.5 % under saline conditions (P<0.05). N removal by plant uptake improved by 26.1 % and 27.7 % under normal and saline conditions due to P. indica-mediated growth-promoting effects. Salt-tolerant denitrifiers and nitrifiers guaranteed the dominant role of microbial degradation in N removal under saline conditions. P. indica inoculation considerably improved the contribution of Nocardioides and Nitrosomnas to dissimilatory/assimilatory nitrate reduction and nitrification genes, respectively. These findings elucidate the mechanisms and potential applications of P. indica-mediated phytoremediation in practical wastewater treatment under varying salty conditions.