Microbial Mechanism Of Bioorganic Fertilizers To Improve Phytoremediation Efficiency Of Heavy Metals-contaminated Saline Soil

At present,under the combined influence of human activities and climate change,the problem of heavy metals-contaminated saline soil in arid and semi-arid regions is increasing,posing a serious threat to the ecological environment and human health in the region.Phytoremediation is one of the ideal techniques to remediate heavy metals-contaminated saline soil,but the remediation efficiency needs to be improved.Leymus chinensis and Puccinellia distans are widely distributed in arid and semi-arid regions and are tolerant to both heavy metals and salt.Bioorganic fertilizers have the potential to improve phytoremediation efficiency.However,the role of bioorganic fertilizers in improving the phytoremediation efficiency of heavy metals-contaminated saline soil and rhizosphere microbial mechanisms are still unclear.In this study,we collected natural heavy metals-contaminated saline soil(total salt content of 9.93 g·kg^-1,dominated by Pb,Cd,As,Zn and Cu complex contamination)from a lead and zinc mining area in Inner Mongolia,and studied the effects of manure bioorganic fertilizer（MOF）and lignite bioorganic fertilizer（LOF）on the growth,heavy metals and salt ion uptake,accumulation and translocation of Leymus chinensis and Puccinellia distans in heavy metals-contaminated saline soil by greenhouse pot experiments.On this basis,the effects of bioorganic fertilizers on the rhizosphere microbial communities of Puccinellia distans were investigated to reveal the potential rhizosphere microbial mechanisms of bioorganic fertilizers to improve the phytoremediation efficiency of heavy metals-contaminated saline soil.The main results of this study are as follows:（1）MOF and LOF treatments significantly increased the total dry weight of Leymus chinensis and Puccinellia distans by 385%to 1157%,improved C:N,C:P,N:P and K⁺/Na⁺,Ca²⁺/Na⁺,P/Na⁺,significantly increased N,P and K concentrations by 19.53%to 224.46%,and significantly improved physiological and biochemical indicators（MDA,CAT,etc.）.（2）MOF and LOF treatments significantly increased the accumulation of heavy metals and salt in Leymus chinensis and Puccinellia distans;MOF caused a significant increase in Zn and Cd translocation rates in Leymus chinensis and Zn,Cd and Na translocation rates in Puccinellia distans;LOF caused a significant increase in Cd translocation rates in Leymus chinensis and Zn,Cu,Cd,Na and Ca translocation rates in Puccinellia distans.（3）MOF and LOF treatments reduced post-planting soil EC to different degrees and improved soil fertility（N,P,K,etc.）and the proportion of soil macroaggregates;MOF caused a significant increase in the concentration of available As in Puccinellia distans soils;LOF caused available As,available Cd concentrations in Leymus chinensis soils and available Zn,available As,available Cd concentrations in Puccinellia distans soils significantly increased.（4）MOF and LOF treatments significantly increased the diversity or richness of bacterial community,with no significant changes in fungi,and improved the microbial community structure.LEf Se analysis showed that MOF and LOF were significantly enriched with beneficial microorganisms with potential functions to improve soil nutrient cycling（e.g.MND1 and Haliangium,etc.）,promote plant growth and alleviate heavy metals and salt stress（e.g.Bacillus,Streptomyces,Iamia,Arachniotus,Acauliums,Devosia,Ohtaekwangia and Nocardioides,etc.）.（5）MOF and LOF treatments enhanced bacterial versatility and fungal stability;Altered microbial network keystones,most of the altered keystones had potential functions to help plants adapt and alleviate heavy metals and salt stress（e.g.Microvirga,Caldicoprobacter,Sphingomonas,Steroidobacter,OLB13,Epicoccum,Coniochaeta,etc.）;enhanced positive correlations between microorganisms and plants,which may help promote plant tolerance and phytoremediation efficiency.The results showed that bioorganic fertilizers can improve plant adaptation and remediation efficiency of heavy metals-contaminated saline soil by promoting plant nutrient uptake,regulating ion balance,improving antioxidant stress capacity,regulating translocation rates of heavy metals and salt;improving soil structure and nutrient status,increasing available heavy metals;and significantly changing rhizosphere microbial communities composition and structure,enriching rhizosphere beneficial microorganisms,and improving bacterial and fungal network structure and interactions.