Response of Astragalus cicer Rhizosphere Soil Properties to Combined Copper and Nickel Stress
Heavy metals persist in soil,impacting the growth and metabolism of soil microorganisms,leading to shifts in microbial community structure.This study investigated the influence of varying copper(Cu)and nickel(Ni)levels on the composition of bacteria in a Cu-Ni polluted farmland soil(Jinchuan Dis-trict,pH 8.3,Cu2+ 261.1 mg/kg,Ni2+ 258.2 mg/kg).The copper-nickel-resistant plant Astragalus cicer cv.Lutana was employed as the test material.A greenhouse pot experiment was conducted to examine the effects of different Cu-Ni solution concentrations(0,100,200,400,800,and 1600 mg/kg)on the biologi-cal characteristics,physical and chemical properties,and the distribution of bacterial community structure in the rhizosphere soil of A.cicer.The results showed that increasing Cu-Ni stress concentrations signifi-cantly increase rhizosphere soil moisture,Cu2+ and Ni2+ contents.Available nitrogen,phosphorus,potas-sium,microbial biomass carbon,nitrogen,and phosphorus,organic matter,as well as Chao 1 richness index,Pielou evenness index,and Shannon and Simpson diversity indices displayed an initial increase fol-lowed by a decrease with increasing stress,and the indicators but available potassium reached their peak at 100 mg/kg Cu-Ni.Conversely,pH value,urease,catalase,dehydrogenase,and alkaline phosphatase activities in the rhizosphere soil all exhibited a reduction with increasing stress.Proteobacteria,Acidobacte-ria,Actinobacteria,Bacteroidetes,and Gemmatimonadetes emerged as the dominant bacterial groups across all samples.Relative abundances of Gemmatimonadetes and Bacteroidetes increased with rising Cu-Ni concentrations,while the relative abundance of Acidobacteria displayed an initial increase followed by a decrease.Actinobacteria relative abundance showed a decline.Redundancy analysis and the Monte Carlo permutation test revealed significant impacts of soil dehydrogenase,pH,and microbial biomass nitrogen on the bacterial community composition.In conclusion,a Cu-Ni concentration of 100 mg/kg appeared to pro-mote the diversity of rhizosphere bacterial community,whereas higher concentrations had an inhibitory effect.
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