THE ROLE OF STEM NODULE IN THE ADAPTATION OF SESBANIA ROSTRATA TO Pb/Zn TAILINGS ENVIRONMENT Ⅱ. THE EFFECT OF STEM NODULE ON NITROGEN AND HEAVY METALS ACCUMULATION OF SESBANIA ROSTRATA
茎瘤对长喙田菁在铅锌尾矿环境适应中的意义II 茎瘤对长喙田菁固氮和积累重金属的影响

The effect of stem nodule on the nodulation, nitrogen fixation and heavy metals accumulation of Sesbania rostrata were investigated by keeping stem nodule or removing stem nodule and grown on Pb/Zn tailings or soil amended tailings or pure soil. The results showed that contents of nitrogen and N-accumulation per plant of S. rostrata in the keeping stem nodule treatments were higher than that in the removing stem nodule treatments for 12.4%-34.0% and 43.3%-131.4%, respectively. The relative contribution of stem nodule to N-accumulation of the plant was more significant when the plant grown on the pure Pb/Zn tailings than on the pure soil and the amended tailings. Root nodules of S. rostrata grown worse in the keeping stem nodule treatments than in removing stem nodule treatments, in particular when the plant grown on the Pb/Zn tailings. It was suggested that S. rostrata forms stem nodule for fixing nitrogen firstly, and when the stress caused by the tailings occurred, S. rostrata would especially fix N with stem nodule rather than root nodule. Therefore, stem nodule plays important roles in obtaining nitrogen and supporting the growth of S. rostrata on the Pb/Zn tailings. Furthermore, the contents of Pb, Zn, Cu and Cd in S. rostrata were a little higher in the removing stem nodule treatments than that in the keeping stem nodule ones and ranked in Zn>Pb>Cu>Cd. The contents of the heavy metals were higher in root than in stem and leaf, and there were no significant difference between stem and leaf for all tested metals. The results proved that S. rostrata is able to fix nitrogen even when growing on the environment polluted with heavy metals.