Influence Of Dark Septate Endophytes On The Lead Tolerance And Transport Of Rice

Heavy metal pollution in farmland ecosystems has become increasingly serious,threatening the grain security and national health of our country.Plant-microorganism combined remediation technology,which is environmental friendly and cheap,has become the focus of current research.In this study,a pot experiment was conducted to analyze the effect of two dark septate endophytes?DSE??Phialocephala fortinii and Phaeosphaeria fuckelii?on Oryza sativa growth under different Pb²⁺concentrations?0,250,500 mg/Kg soil?.Moreover,the differences in physiological characteristics?photosynthesis,cell membrane lipid oxidation,root vigor,antioxidative enzyme systems and antioxidants?,pH value of rhizosphere soil,lead uptake and translocation of O.sativa were compared between DSE inocolated and uninoculated plants.Furthermore,the possible mechanism on DSE improving the lead tolerance of O.sativa was analyzed.This study could provide the theory basis for the application of DSE in the control and vegetation restoration of heavy metal lead pollutted farmland ecosystems.The main results and conclusions were listed as follows:1.Two DSE isolates,P.fortini and P.fuckelii,were screened from nine with higher lead tolerance and could establish a better symbiotic relationship with O.sativa root,and were used for the next step.2.Under lead stress,DSE inoculation could increase the biomass of O.sativa when compared with uninoculated plants,in particular,promote the tillering and root growth,higher lead stress,bigger improving effect.Compared to the effects of P.fuckelii,P.fortinii showed a better ability of promoting the growth of O.sativa under lead stress,which may be related to its higher colonization rate.3.The photosynthetic rate,transpiration rate and stomatal conductance of uninoculated plants were declined under lead press,but their intercellular carbon dioxide concentrations were increased.DSE inoculation showed a positive effect on the photosynthesis of O.sativa,especially on the net photosynthetic rate which were increased by 32.1%-86.8%and24.5-54.9%,respectively.Transpiration rate and stomatal conductance of O.sativa leaves were significant increased under higher lead stress.Moreover,the leaf intercellular carbon dioxide concentrations were reduced about 19.5-40%when inoculation with P.fortini.The membrane lipids of O.sativa leaf cells were damaged by lead stress,resulting in a rapid increase in malondialdehyde contents and leakage of electrolytes.DSE inoculation reduced the contents of malondialdehyde and electrolyte leakage in the leaf cells,so that the damage of membrane lipids caused by lead poisoning were declined.4.Under lead stress,the activities of superoxide dismutase?SOD?and peroxidase?POD?in two DSE inoculated O.sativa leaves were increased by 27.8%-185%and 39%-64%,respectively.In addition,P.fortini and P.fuckelii inoculation increased the activity of leaf catalase?CAT?by 1.4-2.9 fold and 1.6-2.3 fold,and the amount of leaf proline by 1.4-1.7 fold and 1.3-1.5 fold,respectively.Compared with uninoculated plants,mycorrhized O.sativa had a higher root vitality,which may be one of the most important reasons for the effect of DSE on improving the lead tolerance of O.sativa.5.Under lead stress,the lead concents in different organs of O.sativa were in roots>leaves>seeds.Compared with uninoculated plants,the lead contents in the DSE inoculated O.sativa roots were higher,but the lead contents in leaves and seeds were lower than those of control.This results showed that more lead content was accumulated in the DSE inoculated O.sativa roots,accompanied by the decrease in lead and seed lead contents.