Resistance And Accumulation Of Heavy Metals In Spartina Alterniflora Under Combined Treatment Of Water Inundation And Heavy Metals

Due to the rapid development of the local industrial and agricultural activities,Yangtze River estuary is threatened by increasing pressure of HMs(HMs)pollution;The sediment physiochemical characters,such as redox potential,organic matter content,pH,etc.,vary greatly with the waterlogging conditions of the estuary wetland,which have great influences on the relocation of HMs in the sediments and plants and toxicities of HMs.Therefore,it is necessary to consider tidal flooding conditions of the estuary wetland(i.e.periodic water inundation),to get a better understanding on the effects of HMs on the growth and physiology of tidal wetland plants and role of plants in accumulation and translocation of HMs.Based on greenhouse controlled experiments and filed investigations,the present study investigated the physiological responses and metals accumulation and translocation of Spartina alterniflora,a typical wetland plant in Yangtze River estuary wetland,to the combined influences from periodic flooding and different concentrations of HMs.The effect of exogenous EDTA on the anti-stress physiology and HMs' accumulation and translocation in S.alterniflora were also studied.The main results are summarized as follows:(1)The height,base diameter,net photosynthetic rate(Pn),transpiration rate(Tr),water use efficiency(WUE)and carboxylation efficiency(CE)of S.alterniflora all increased significantly under the treatments of low levels of combined treatments of HMs(1HMs and 2 HMs),but significantly inhibited by high levels of HMs treatment(4HMs).The concentrations of stress hormones jasmonic acid(JA),abscisic acid(ABA)and ethylene(ethylene),and the activity of major antioxidant enzymes,such as superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX),alcohol dehydrogenase(ADH),all decreased gradually with the increase of the HMs.Result showed that S.alterniflora was somehow tolerant to the combined HMs treatments as evidenced by their unaltered leaf Chl content under low to moderate level of HMs.S.alterniflora showed low HM uptake ability indicated by the relative low translocation factor(TF)for Cu,Zn,Pb and Cr,which implies this plants is not a good candidates for traditional phytoremediation of wetland HM pollution.Root of S.alterniflora accumulated large quantities of Cu,Zn,Pb,and Cr,which suggest that S.alterniflora might help to remove and purify the sediment HM pollutants through the immobilization of HMs in rhizosphere.(2)Long time of water inundation and HMs(12h+HMs)treatment significantly increased leaf Pn,WUE,POD and SOD activities of S.alterniflora,but showed no signs of victimization and obvious damage in apparent form,indicate the tolerance of this plant to water inundation.The photosynthetic physiology of this plant was peaked under 6 h per day water inundation treatment with the same strength of HM stress,suggested that the species had the highest HMs tolerance under 6 h per day of water inundation treatments.Changes in leaf MDA and JA contents of S.alterniflora showed similar trends between the greenhouse different water inundation experiment and the field investigation at different tidal levels.Compared to the other parameters,leaf ABA content and Pn are more sensitive to the combined treatment of water inundation and HMs,which have the potential to be used as ecological indicators for plant in response to environmental stresses.According to the results of present study,long time of water inundation treatment favored the retention of HMs in the sediments and the accumulation of HMs in plants.In the construction of artificial wetlands for wastewater treatment,the water inundation time must be seriously considered to attain relatively healthy plant growth and high waste removal efficiency.(3)The high level of combined HMs(4HMs)treatments,though not lethal,did harm to the growth and physiological function of S.alterniflora.Application of EDTA favored the uptake of HMs in leaves and roots of S.alterniflora,but showed apparent toxic effect at the same time.With the increasing of exogenous EDTA concentrations,the height,basal diameter,tiller number,Pn,Tr,WUE and CE,as well as the major antioxidative enzymes activities of S.alterniflora were all significantly depressed,and the leaf MDA content increased significantly,suggested that the severe lipid peroxidation occurred due to the treatment of EDTA and HMs.