| Ectomycorrhizal fungi are wide-spread in forest ecosystems and play an important role in the phyto-microbial remediation technology of heavy metal contaminated soils.It is of great significance to study the physiology and molecules of ectomycorrhizal fungi-plant symbionts in promoting plant growth and reducing the toxicity of Cd to the plant and microbe joint remediation of Cd contaminated soil.In this study,two ectomycorrhizal fungi Suillus luteus and Cenococcum geophilum were selected for mutual symbiosis with the new willow species(salix psammophila 'Huangpi1')to explore the tolerance mechanism of mycorrhizal and non-mycorrhizal willow to Cd under Cd stress.Root transcriptome sequencing further explains the molecular mechanism of ectomycorrhizal fungi on promoting Cd tolerance in willows.Secondly,the relevant indicators of mycorrhizal and non-mycorrhizal willow rhizosphere soil microenvironment were measured to comprehensively analyze the mechanism of ectomycorrhizal fungi to repair soil heavy metal Cd with willow.The main conclusions are as follows:1.The dry weight of leaves,stems and roots of the willow seedlings was increased after inoculation with Suillus luteus and Cenococcum geophilum.After Cd stress,the growth of the whole root system of the plant was significantly affected.Compared with non-inoculated willow seedling,the root surface area and root length of the seedlings inoculated with Cenococcum geophilum increased by 34.6% and 14.6%.The root surface area and root length of the plant inoculated with Suillus luteus increased by 32.6% and 1.4%,respectively.The formation of ectomycorrhiza can promote the growth of willow seedlings.The inoculation of Cenococcum geophilum has a better promotion effect on the growth of willow seedlings.Cd stress reduced the net photosynthetic rate of the willow,but the net photosynthetic rate was significantly increased after the willow was inoculated with ectomycorrhizal fungi.The intercellular carbon dioxide concentration was significantly reduced,and the inoculation of the ectomycorrhizal fungi had a positive effect on plant photosynthesis.In particular,the inoculation of Cenococcum geophilum has a more obvious promotion effect on the photosynthesis of willow leaves,which can better alleviate the toxic effect of plant growth under Cd stress.2.The content of MDA under Cd stress increased significantly in both the non-inoculated and inoculated treatments.Comparing with the MDA content of the roots in each treatment,the MDA content produced by the non-oculation with Cenococcum geophilum was significantly lower than the non-inoculated treatment,indicating that the inoculated treatment has a certain protective effect on willow seedlings and reduced the damage of heavy metal Cd.The test results of antioxidant enzymes and non-enzymatic indicators showed that,compared with the inoculation of Suillus luteus,inoculation with Cenococcum geophilum can more significantly stimulate the antioxidant system in the willow.The Cd stress group significantly increases the activity of CAT in the leaves,and the activity of inoculation with Cenococcum geophilum is higher.The SOD activity under Cd stress was higher than that of no Cd stress.The SOD activity in the roots of the willow in the treatment group inoculated with Cenococcum geophilum was generally lower than that of the non-inoculated group,indicating the defence mechanism in roots and leaves was different.For non-enzymatic antioxidants,the content of GSH in leaves showed a significant upward trend in the treatments with Cd and inoculation with Cenococcum geophilum,but there was no significant difference in other treatment groups.The content of ASA in roots also showed significant differences under the treatment of inoculating with Cenococcum geophilum,and its content under Cd stress was higher than that of the control without Cd.3.Different inoculation treatments showed similar Cd enrichment mechanisms.The roots of willow seedlings showed the largest accumulation of Cd,while the leaves and stems showed no significant difference was observed in the accumulation of Cd;the contents of five nutrient elements in the willows were : K > Mg > Ca > Fe > Zn,the presence of Cd can increase the content of Fe,Zn,and K to a certain extent,and promote the absorption of the elements.4.Transcriptome sequencing data showed that there were 1711 genes differentially expressed between inoculating with Cenococcum geophiluma and non-inoculated willow seedling,of which 1340 genes were up-regulated and 371 genes were down-regulated.Between inoculating with Suillus luteus and non-inoculated willow seedling treatment,766 genes were significantly different,of which 597 genes was up-regulated,and 169 genes were down-regulated;the species closely related to willow is Populus pilosa,with a species similarity of 55.61%,and Populus euphratica with a species similarity of 28.48%;the KEGG pathway of the differential genes in the two comparison groups was mainly enriched in carbohydrate metabolism pathway.5.The Cd form of the rhizosphere soil showed similar proportion distribution under different inoculation treatments.The exchangeable Cd content of the inoculation treatment accounted for the highest proportion of the five Cd forms.The treatment group inoculated with Cenococcum geophilum had higher exchangeable Cd content,accounting for 36.7% of the total.The content of carbonate bound state and residue state is second only to exchangeable state,and the content of iron manganese oxidation state and organic bound state is the least and the percentage was basically the same.6.Under Cd stress,the three rhizosphere soil enzymes all showed a downward trend.After inoculation with ectomycorrhizal fungi,the activities of catalase,urease and acid phosphatase under the same Cd treatment were significantly enhanced,especially when inoculated with Cenococcum geophilum.Thus,the inoculation of Cenococcum geophilum can more significantly enhance the activities of catalase,urease and acid phosphatase in the rhizosphere of willow under Cd stress,thereby alleviating the oxidative stress of Cd to the rhizosphere and improving the tolerance of willow to oxidative stress. |
PDF Full Text Request