| Manganese(Mn)mining brings economic benefits,but it leads to manganese pollution and affects the normal production and life of people in the mining area and surrounding areas.Lespedeza davidii is a shrub in the family Fabaceae,which has the advantages of high biomass,strong stress resistance,and biological nitrogen fixation.This plant can grow and bloom normally in the abandoned land of Xiangtan manganese mine,and is an important species for ecological restoration in mines.Arbuscular mycorrhiza fungi(AMF)are a kind of soil microorganisms that can coexist with more than 80%of plants on land and form mycorrhizal structures.In heavy metal contaminated soil,AMF symbiosis with plants can affect the absorption,transport and accumulation of heavy metals,enhance the tolerance of plants to heavy metal toxicity,and promote the growth and development of plants.To reveal the mechanism of AMF-plant symbiotic remediation of soil Mn pollution,this study used Funneliformis mosseae(Fm)which is widely used AMF as the inoculum material and L.davidii as the host plant.Two treatment groups were set up,with(Fm+group)and without Fm(Fm-group)inoculation.A pot experiment was conducted to compare the effects of inoculation with Fm on seed germination,seedling growth,leaf anatomical structure,physiological and biochemical characteristics,Mn enrichment characteristics,Mn subcellular components,and chemical morphology of L.davidii under different Mn concentrations(0,1,5,10 and 20 mmol/L).The results showed that:(1)With the increase of Mn concentration,the germination rate of L.davidii seeds gradually decreased,and both were higher than 60%.The germination rate and germination index of the Fm-group were higher than those of the Fm+group.With the increase of Mn concentration,the biomass and root to shoot ratio of seedlings first increased and then decreased,reaching their highest values at a Mn concentration of 5 mmol/L;and the Fm-group was lower than the Fm+group.(2)With the increase of Mn concentration,the plant height,leaf area,specific leaf area,root crown ratio,biomass,total root length,root volume,root surface area,root diameter and root tip number of L.davidii all showed a first increase and then a decrease,and the Fm-group was lower than the Fm+group.(3)With the increase of Mn concentration,the leaf total thickness,upper epidermis thickness,lower epidermis thickness,spongy tissue thickness,palisade/spongy tissue ratio,and organizational compactness of L.davidii increased first and then decreased,and the Fm-group was lower than the Fm+group.When the Mn concentration was 20 mmol/L,the leaf total thickness,upper epidermis and lower epidermis of Fmgroup were 19.8%,12.6%and 35.5%lower than those of Fm+group respectively,and the thickness of palisade tissue,thickness of spongy tissue,palisade/spongy tissue ratio and organizational compactness were 22.0%,84.8%,10.3%and 15.8%lower than those of Fm+group respectively.(4)With the increase of Mn concentration,the content of photosynthetic pigments,osmoregulation substances,and peroxidase activity in L.davidii leaf first increased and then decreased,and the Fm-group was lower than the Fm+group.At a Mn concentration of 20 mmol/L,the soluble sugar,soluble protein,and free proline contents in the Fm+group were 2.25 times,2.70 times,and 1.26 times higher than those in the Fm-group,respectively.The SOD,POD,and CAT activities were 1.26 times,1.33 times,and 2.94 times higher than those in the Fm-group,respectively.As the Mn concentration increases,the MDA content gradually increases,and the Fm+group is lower than the Fm-group at different Mn concentrations.(5)With the increase of Mn concentration,the root,stem,leaf,and total Mn content of L.davidii gradually increase.When the Mn concentration is 20 mmol/L,the Mn content in the plants shows as follows:stem>root>leaf;The Mn content in the Fm+group is higher than that in the Fm-group.The bioconcentration factors of L.davidii was greater than 1 at all Mn concentrations,and the translocation factor of the Fm+group was lower than that of the Fm-group.The Fm+group reached its highest value of 2.45 at a Mn concentration of 10 mmol/L,while the Fm-group reached its highest value of 2.88 at a Mn concentration of 20 mmol/L.(6)With the increase of Mn concentration,the Mn content in each subcellular of the roots,stems,and leaves of L.davidii gradually increases,and the proportion of Mn content in cell wall fraction and ribosomes fraction is relatively high.At a Mn concentration of 20 mmol/L,the Mn content in the root cell wall fraction of the Fm+group and Fm-group was 11.4 times and 9.1 times higher than that of the control,77.0 times and 98.0 times higher in the stems,32.5 times and 9.8 times higher in the leaves,respectively.(7)With the increase of Mn concentration,the content of various chemical forms of Mn in the roots,stems,and leaves of L.davidii increases.The Mn content of NaCl form in roots and stems is highest at low Mn concentrations,while the Mn content of d-H2O form is highest at high Mn concentrations.When the Mn concentration is below 10 mmol/L,the Mn content of NaCl form in roots and stems is higher,and the Fm+group is greater than the Fm-group.The results of this study indicate that high Mn stress can inhibit the growth of L.davidii,while Fm can promote plant growth.Fm can enhance the fixation of heavy metals in the cell walls and vacuoles of plants,promotes the transformation of strongly active Mn into weakly active forms;At the same time,it,can alleviate the toxic effects of Mn stress by increasing the content of osmoregulation substances and peroxidase activity and improves the tolerance of L.davidii to Mn stress. |
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