| In recent years,with the acceleration of urbanization and industrialization and the overuse of chemical pesticides,soils in different regions may be affected by both salinization and heavy metal pollution.Studies have shown that halophytes are the best choice for phytoremediation of heavy metal-contaminated saline soils,but their growth may be significantly affected under combined stress,resulting in low remediation efficiency.Arbuscular Mycorrhizal(AM)fungi can improve plant tolerance to heavy metal or salt stress,but the molecular mechanism of AM fungi on improving halophyte growth and tolerance under the combined treatment of heavy metal and salt has not been studied.In this paper,a greenhouse pot experiment was conducted to simulate cadmium(3.0 mg·kg-1)contamination of NaCl-type salinization(0,6.0,12.0 g·kg-1)soil.To study the effect of AM fungi Funneliformis mosseae(F.mosseae)on the growth,Cd and Na+uptake and transport,rhizosphere soil physicochemical properties,and plant metabolomics regulation,and so on,of Suaeda salsa.These results revealed the mechanism of AM fungi enhancing the growth and tolerance of Suaeda salsa under the combined treatment of heavy metals and salt.The test results are as follows:(1)In different degrees of Cd-contaminated saline soil,AM fungi successfully established a symbiotic relationship with Suaeda salsa.The average the mycorrhizal colonization rate was 11.25%?26.37%,and it decreased significantly with the increase of salt concentration.(2)Under the combined treatment of 3 mg·kg-1Cd and 0 g·kg-1NaCl,AM fungi significantly increased the shoot and root biomass of Suaeda salsa by 42.1%and 329%,and the contents of phosphorus,calcium,potassium and magnesium in the shoots and roots were significantly increased by 9.94%?48.6%,the Cd accumulation in the shoots increased significantly by 30.6%.(3)Compared with 0 g·kg-1salt treatment,6.0 g·kg-1salt treatment significantly increased the shoot biomass of Suaeda salsa by 14.9%?36.4%.Under the combined treatment of 3 mg·kg-1Cd and 6 g·kg-1NaCl,AM fungi significantly increased the shoot and root biomass of Suaeda salsa by 68.7%and 88.9%;and the contents of phosphorus,calcium,potassium and magnesium in the shoots and roots were significantly increased by 7.5%?45.6%;the accumulations of Na+and Cd in the shoots were significantly increased by 28.0%?107%,and the Na+and Cd transport factors were significantly decreased by 27.2%and 107%.The content of proline,soluble sugar,and the activity of antioxidant enzyme CAT in leaves were significantly increased,while the content of malondialdehyde(MDA)was significantly decreased.(4)Compared with 0 g·kg-1salt treatment,12.0 g·kg-1salt treatment significantly decreased the shoot biomass of Suaeda salsa;AM fungi has no significant effect on the biomass of Suaeda salsa,but it significantly increased the content of phosphorus in the shoots and roots by 264%,the accumulation of Cd in the shoots increased by 264%,and the transport factor of Cd was significantly decreased by 33.9%.(5)Under the combined treatment of 3 mg·kg-1Cd and 6 g·kg-1NaCl,a total of 85 differential metabolites were obtained from the shoots of Suaeda salsa inoculated with AM fungi(62 was up-regulated,and 23 was down-regulated).According to differential metabolite expression,KEGG enrichment and i Path pathway analysis,AM fungi significantly regulated the synthesis and metabolism of key amino acids in Suaeda salsa,among them 2-hydroxycinnamic acid,dopaquinone and 5-hydroxy-L-chromophore which were as to be the antioxidants could scavenge the highly active oxygen free radicals generated under the stress and improve the anti-oxidative stress ability of Suaeda salsa,and the activation of tyrosine and tryptophan metabolic pathways significantly improved the abiotic effects of Suaeda salsa.AM fungi significantly regulated the synthesis and metabolism of plant endogenous hormones,among them salicylic acid and jasmonic acid could induce and enhance the antioxidant capacity of plants,and the increase in the expression level of indoleacetic acid can increase the biomass of Suaeda salsa.AM fungi significantly regulated the synthesis and metabolism of glycolysis and gluconeogenesis metabolites of Suaeda salsa,of which 1-Sucrose and arbutin were the main substrates and precursors of macromolecular soluble sugars,the increase of their expression levels could increase the content of soluble sugars in it,thereby enhancing the ability of it to resist osmotic stress.The results showed that under the combined treatment of heavy metal and salt,AM fungi could significantly improve the growth of Suaeda salsa,promote the accumulation of Cd and Na+,and enhance the antioxidative and osmotic stress resistance of it,regulate the expression levels of plant hormones,amino acids and sugar-related metabolites,thus improved the tolerance of Suaeda salsa to the combined treatment of heavy metals and salt.It was proved that AM fungi had the potential to improve the phytoremediation efficiency of heavy metal-contaminated saline soils.The research results could provide theoretical basis and technical support for the combined use of AM fungi and Suaeda salsa to remediate heavy metal-contaminated saline soils. |
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