Mixed nitrogen form addition facilitates the growth adaptation of legume plant to heavy metal contamination in degraded mining areas

Abstract

High speed development of the mining industry has lead to serious heavy metal pollution problems around mining areas in China, such as contaminating soil, and threatening the health of ecosystems and local residents. Plants long-term grown in mining areas largely show high adaptive capacity to the environment and facilitate the reclamation of degraded lands. In this study, we tested whether and how nitrogen form affect the adaptive capacity to soil contamination between legume (Robinia pseudoacacia) and nonlegume (Rhus chinensis) plants, typical phytoremediation species for soil environments polluted by heavy metals in China. All growth parameters and leaf catalase (CAT) and peroxidase (POD) of plant species were significantly greater in control than in contamination soil, in legume than in nonlegume, and in 50% NO3− (nitrate)+ 50% NH4+ (ammonium) and 100% NH4+ than in without and 100% NO3− treatments. The negative effect of soil contamination on all growth parameters was significantly stronger in nonlegume than in legume plant. Legume plant produced greater total mass, root mass and leaf mass in 50% NO3− + 50% NH4+ and 100% NH4+. Furthermore, the positive effect was not influenced by soil contamination. The greater physiological response to soil contamination in nonlegume plant and mixed addition of NO3− and NH4+ greatly relieved heavy metal stress on plants, especially in nonlegume plant. Mixed addition of NO3− and NH4+ greatly increased transfer factor for Pb and Zn and the positive effect significantly greater in nonlegume than in legume plant. Mixed addition of NO3− and NH4+ greatly increased the performance and adaptation of legume in contamination environment. To some extent, multiple N form addition in soil contamination environment may facilitate high plant adaption in phytoremediation, and using legume plants with mixed addition of NO3− and NH4+ is largely an important restoration mode for degraded mining areas.