Microplastics (MPs) increase the effective state of heavy metals (HMs) in soil and seriously threaten the yield and quality of peanuts (Arachis Hypogea L.). Kaolinite (KL) has the potential to ameliorate MP- and HM- contaminated soils, but the mechanism of action between them is not well understood. Therefore, 60-day experiments were conducted, where KL (1 %, 2 %) and MPs (0.1 %, 1 %) were individually or jointly mixed into soils with different cadmium (Cd) concentrations (0.5, 2.5, and 5.0 mg·kg-1) to cultivate peanuts in a greenhouse. Finally, soil-bioavailable Cd, peanut dry weight, peanut Cd concentrations, the pH, cation exchange capacity (CEC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were determined. It was shown that MPs negatively affected the peanut dry weight and increased the content of soil-bioavailable Cd and Cd concentration in peanut. In the MP- and Cd-contaminated soils, KL mitigated the negative influence of MPs by increasing the dry weight of peanuts by 8.40 %-40.59 %, decreasing the soil-bioavailable Cd by 23.70-35.74 %, and significantly decreasing peanut Cd concentrations by 9.65-30.86 %. The presence of MPs decreased soil pH (7.69-7.87) and the CEC (20.96-23.95 cmol·L-1) and increased the soil DOC (1.84-2.26 mg·kg-1). KL significantly increased soil pH (7.79-8.03) and the CEC (24.96-28.28 cmol·L-1) and mitigated the adverse influence of MPs on the pH and CEC of Cd-contaminated soils. A regression path analysis (RPA) evidenced that KL decreased Cd accumulation in plants by changing the properties of soil contaminated with MPs and Cd. The research results revealed the mechanism of KL on peanut growth and Cd absorption in MP- and Cd-contaminated soil. The results of this study provide a foundation to improve the quality of MP- and HM-contaminated soils and realize safe peanut production.
ABSTRACT Soil is the natural habitat for microorganisms, providing water and nutrients for vegetation, but the influence of meadow degradation on the “vegetation‐soil‐microorganism” system is still controversial, and the drivers of soil microbial and vegetation characteristics change are still unclear. This study explores in‐depth the vegetation and soil changes in four different degradation levels, that is, non‐degraded (ND), lightly degraded (LD), moderately degraded (MD), and severely degraded (SD), in the northeastern region of the Qinghai‐Tibetan Plateau. Soil metagenomic sequencing methods were employed to understand the soil microbial and functional diversity and the factors that influence them. The findings indicated that alpine meadow degradation decreased the vegetation height, coverage, and above‐ground biomass (AGB), but increased the vegetation diversity index. In addition, meadow degradation reduces soil properties (organic carbon, total nitrogen and phosphorus, available nitrogen and phosphorus) and enzyme activities (sucrase, cellulase, urease, and catalase) but increases soil pH. The copiotrophic groups (Actinobacteria, Ascomycota) decreased while oligotrophic groups (Acidobacteria, Glomeromycota) increased with meadow degradation. In particular, changes in vegetation characteristics and microbial community structure in alpine meadows are strongly influenced by changes in soil pH. In conclusion, the degradation of alpine meadows leads to the growth of some barren‐tolerant species and deviation of soil pH from neutrality, which increases vegetation diversity but surface exposure reduces the vegetation richness, affects the type and amount of root secretions and changes in soil microbial communities, which reduce the fixation and release of soil nutrients. This study provides the theoretical basis for further analyzing the inner mechanism of alpine meadow degradation.
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