The Tolerance And Morph-Physiological Responses Of Switchgrass To Cadmium

Cadmium(Cd)contamination and energy crisis have become a very serious problem with society development.How to develop and use Cd-polluted soil and find an alternative energy have become a research topic.Recently,plant bioenergy has been a worldwide concern because of its safety,clean,reproducing and low input.Switchgrass is a warm-season perennial(C4)tall grass that is native to the Canada、United States and Mexico,but is most abundant in North America.The grass has been recognized as a potential biomass feedstock for biofuel production in North America by the United States Department of Energy because of its wide adaptation and abundant cellulose.In this study,the plant was chose to evaluate its tolerance to Cd.And the morph-physiological responses of switchgrass to Cd was also studied.The results of the research may provide a reference for further study of switchgrass tolerance to Cd and develop bioenergy plant in Cd-polluted soil.The results were as below:1、Growth of guinea grass and switchgrass was significantly affected by Cd,especially for guinea grass.Therefore,guinea grass may not be developed as a bioenergy plant under Cd polluted condition,switchgrass can grow in middle and heavy Cd contaminated environment.What’s more,the result showed that root morphology can be an important index that evaluate Cd tolerance of plant,and fine root may play an important role in Cd accumulation of plant.2、Compared with Blackwell and Shawnee,Alamo and Newyork have higher translocation for Cd from root to shoot at seedling stage.The result of comprehensive evaluation showed that Cave-in-Rock and Alamo were more tolerant to Cd,Newyork was most sensitive to Cd under hydroponic culture at seedling stage.3、The growth and root morphology of switchgrass were affected by Cd stress.Biomass,water content,chlorophyll content,total root length(RL),root surface area(RA),root volume(RV)and number of root tips(RT)were decreased,but root average diameter(RD),root/shoot ratio and Cd accumulation were increased under Cd stress.Cave-in-Rock could accumulate more Cd than Alamo,and RL,RA and RV of Cave-in-Rock were significantly higher than Alamo in the 0.3-0.9 mm diameter classes.Which suggested that a well-developed root system may contribute to higher Cd accumulation in Cave-in-Rock.4、It seemed that a high proportion of Cd was in the soluble fraction(mainly in vacuoles),a lowest proportion of Cd was in organelle fractions.Which meant that the high proportion of Cd in soluble fraction limited root-to-shoot translocation of Cd and reduced shoot Cd levels.Magnesium(Mg)content in root,iron(Fe)content in shoot,zinc(Zn)and manganese(Mn)content of switchgrass were dramatically decreased under Cd stress,but the translocation factors of Mn and Mg were significantly increased.Photosynthesis of the grass was significantly inhibited by Cd,Cave-in-Rock showed a better photosynthetic capacity in low Cd concentration(2 μmol/L),but which was inverse in high Cd concentration(20 μmol/L).Stomatal limitation was involved in the photosynthesis decrease of Alamo but not in Cave-in-Rock under Cd stress.There was a positive correlation between root morphological indicators and net photosynthesis rate(Pn),stomatal conductance(Gs)as well as transpiration rate(E).However,a markedly negative correlation between root morphological indicators and TFs of Mn was observed.There was no correlationship between root morphological indicators and TFs of Fe and Mg.These results indicated that switchgrass would increase Mn translocation from root to shoot under Cd stress,which may be an important strategy for keeping higher photosynthesis.