Study On The Response Mechanism Of Paulownia Fortunei Under Manganese Stress And Modified Manganese Slag

Our previous studies found that the fast-growing tree Paulownia fortunei has the tolerability to Mn.The spent mushroom compost(SMC)was found to be a good modifier through a lot of screening tests.However,the effect of SMC on the mechanism of Mn tolerance of P.fortunei remains unclear.In this study,P.fortunei was used as material,and pot experiments with different Mn concentration were set.It explored the characteristics of Mn enrichment and the mechanism of Mn stress.Using Mn slag as substrate and SMC as modifier,the characteristics of Mn enrichment and the mechanism of Mn stress were studied,and the the tolerability of P.fortunei to Mn was revealed.1.The response mechanism of P.fortunei under Mn stress(1)P.fortunei had the high tolerability to Mn,which could fix with Mn by developed roots.Low concentration of Mn promoted root growth and increased plant tolerance,and maintained the normal operation of a series of life activities in cells,so that P.fortunei could grow normally.While high concentration of Mn inhibited the growth and development of P.fortunei.(2)Under low Mn stress,the activities of SOD and CAT were increased to clear free radicals,and the cell damage was relieved,which improved plant tolerability to Mn.However,excess Mn inhibited the antioxidant enzyme system and the growth of P.fortunei.(3)The cell wall was an important part to fix Mn,and Mn accounts for 39%-90%of the cell wall components.Mn was mainly enriched in the root of P.fortunei.Stable compounds were formed by combining Mn with the root cell walls,which could reduce the transport of Mn to the aboveground and the toxicity to stem and leaf.With the increasing concentration of Mn,the fixation ability of cell walls decreased,and the organelles were further poisoned by Mn.In the root,stem and leaf of P.fortunei,Mn mainly existed in the inorganic salts and amino acid salts,and pectates and protein forms,totaling 57%-86%.With the increasing concentration of Mn,the migration activity of Mn was enhanced,and the Mn toxicity was deepened.(4)TEM analysis showed that Mn stress caused the damage of cell walls of P.fortunei,and made organelles blur.Especially the cell internal structure was seriously destroyed under high Mn stress,which affected the operation of life activities in cells.FTIR analysis showed that P.fortunei could bind Mn to form stable compounds by increasing functional groups,such as-CH3,-COOH,N-H.With the increasing concentration of Mn,the fixation capacity of the cell wall was weakened.Thus,the toxicity of Mn was deepened,which inhibited the growth of P.fortunei.2.The response mechanism of P.fortunei under modified Mn slag(5)SMC amendment made the slag loose,and improved the slag permeability and fertility.It fixed more heavy metal by the chelation of organic matter,and reduced the toxicity of heavy metals in soil.The SMC amendment could facilitated the growth of plant roots,and improved the phytoremediation capacity of P.fortunei for Mn slag.(6)Mn slag stress produced a lot of free radicals to damage the leaf cells of P.fortunei,and destroyed the chloroplast structure,and inhibited the photosynthetic metabolic process.Then,plants initiated antioxidant defense mechanisms to resist stress.SMC amendment removed excess free radicals in cells by increasing antioxidant enzyme activities,reducing the degree of cell membrane lipid peroxidation by 25%-48%.The chlorophyll content in P.fortunei leaves increased by 46%,which was beneficial to the operation of photosynthesis and metabolism.(7)The fixation of cell wall and the compartmentalization of vacuole were the important reasons for Mn tolerance of P.fortunei.Mn was mainly in the cell wall components(57%-84%)and soluble components(8%-41%).SMC amendment enhanced the ability of cell wall and vacuolar substances to bind Mn,and reduced the Mn toxicity to organelles.In the root,stem and leaf of P.fortunei,Mn was mainly in pectates and protein forms(49%-82%),followed by organic salts forms(3%-35%).The SMC amendment enabled the transformation of Mn to the extraction state with weak migration activity to form stable compounds,and reduced Mn toxicity.(8)TEM analysis showed that caused the cell structure of P.fortunei root,stem and leaf was destroyed under heavy metal stress,and the cell wall was deformed and the organelles were disintegrated.The SMC amendment could effectively alleviate the effect of Mn stress on P.fortunei tissues,and reduce the cell damage,thus maintain the normal operation of life activities in cells.FTIR analysis showed that the addition of SMC could increase the functional groups such as-CH3 and-COOH,which combined Mn to form stable compounds by chelation,and then reduced Mn toxicity.