| The heavy mental contaminated soil has become increasingly serious environmental problems in China.As an eco-friendly technology,phytoremediation has aroused hot concern.However,common plants used for remediation have some problems,such as small biomass,low economic benefits and so on.Using energy plants to remediate heavy metal contaminated soils cannot only keep heavy mental away from the food chain but also provide livestockfor the biodiesel industry.Therefore,it is supposed to bring environmental benefits,economic benefits as well as rproducing renewable energy.A pot experiment was conducted to investigate Cd accumulation in energy crop Ricinus communis L.with different Cd doses in soil(0,10,25,50,100,200 mg?kg-1).The result shows thatR.communis adapts well to the concentrations of Cd between 0 and 100 mg?kg-11 in soil,and the Cd contents and uptakes in roots,stems and leaves increase with elevating Cd supply in soil.While the high dose Cd in soil(200mg?kg-1)significantly inhibited the normal growth and decrease the Cd accumulation in R.communis.It can be concluded that R.communis has good tolerance to low and moderate Cd(0-100mg?kg-1))contaminated soil.A hydroponic experiment was carried out to study the changes of chlorophyll contents,MDA contents,antioxidant enzyme activities in R.communis leaves with different doses(0,10,25,50,100,200 and400?mol·L-1).The result suggests that contents of photosynthetic pigment content decreased under Cd stress,while Cd treatments show less effect on the contents of carotenoid which protect content of chlorophyll and clear the role of reactive oxygen species.There is no significant differences of MDA contents between all Cd treatments,indicate the strong antioxidant capacity of R.communis leaves.The activity of SOD and POD was effected under the different Cd concentration,and the activity of POD in the leaves represents effective defense strategies and plays a positive role in Cd tolerance.A hydroponic experiment was conducted to investigate subcellular distribution and chemical forms of Cd in the root and shoot of R.communis with different Cd treatments.The Cd subcellular distribution is in the order of soluble fraction>cell wall>organelle in both roots and leaves.In addition,the Cd accumulation percentages in cell wall show increasing trend with elevating Cd supply.Therefore,vacuolar compartmentalization and cell wall binding are supposed to be the main tolerance mechanism to Cd in Ricinus communis.Furthermore,with increasing Cd supply in the medium,the Cd accumulation percentages in NaCl-extractable fractions increased,whereas Cd extracted by ethanol and water decreased.Therefore,transferring of chemical forms was supposed to be anthor important tolerance mechanism to Cd for R.communis.Hydroponic experiment and pot experiment were both conducted to selecte the optimal exogenous chelating agents and application modes.The result shows that tartaric acid was effective for Cd detoxication,and lactic acid was effective for Cd translocation in R.communis.The Cd concentration in R.communis increased significantly in EDTA and EGTA treatments,but they are also demonstrated toxic effects on plant biomass.There is no significant differences of biomass between the two application modes of chelatingagents,but several times applying mode can significantly enhance the shoots of Cd accumulation ability compared to one-time appllication mode.A pot experiment was performed to study the effectiveness of tartaric acid and EGTA and their combined use in enhancing remediation of Cd contaminated soil with R.communis,so as to discuss the feasibility of chelating agents and antidote in phytoremediation of heavy metal contaminated soil.The results showed EGTA&tartaric acid treatment could significantly increase acetate-extractable Cd concentrations in soils and the acetate-extractable Cd concentrations were 1.41-2.49 times higher than the control.The Cd concentration in R.communis shoots increased significantly in EGTA treatments,but high dose of EGTA demonstrated toxic effects on plant roots.The EGTA&tartaric acid treatments were more effective for Cd detoxication,translocation and biomass accumulationTherefore,EGTA combined with tartaric acid can effectively improve Cd accumulation capacity in R.communis.shoots by adjusting Cd bioavailability and reducing it physiological toxicity.A pot experiment was conducted to investigatethe influence of foliar spraying of phosphate fertilizer?0.2%?0.4%?0.6%?on Cd accumulationin Ricinus communis L.with the Cd concentration of 100mg·kg-1.The results showed that exogenous P could significantly improve Cd concention and biomass accumulation in R.communis,and 0.4%phosphate fertilizer has the best effects.A hydroponic experiment was conducted to investigate the influence of foliar spraying of 0.4%phosphate fertilizer?P?on the physiological and biochemical mechanisms in R.communis with different Cd doses(50,100,150?mol?L-1).The results showed that P foliar spraying significantly increased the photopigment contents.Foliar spraying of P significantly increased Cd concentration in the roots,but Cd contents in shoots and leaves showed no significant difference.The proportions of Cd in the cell wall increased,while that in cell organelle decreased.It is supposed that P addition can strengthen cell wall binding,so as to limit Cd translocation and reduce its physiological toxicity in plants.They may be the main tolerance mechanisms for P foliarspraying to increase Cd accumulation capacity in root and alleviate Cd stress in R.communis. |
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