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Cadmium (Cd) contamination presents a serious challenges for sustainable agriculture. This study evaluated the combined impact of arbuscular mycorrhizal fungi (AMF) inoculation and intercropping with Solanum nigrum on soil microbial diversity, enzyme activity, and environmental factors in soybean cultivation under high Cd stress. The combined treatment effectively reduced bioavailable Cd in soil, with the acid-soluble Cd fraction at 19.57 mg/kg and the reducible Cd fraction at 61.35 %, resulting in safe soybean grain Cd levels (2.63 mg/kg, below the 3 mg/kg organic standard). Illumina NovaSeq sequencing analysis revealed that key bacterial taxa, including Bradyrhizobium and PMMR1, were correlated with reduced Cd uptake in grains. Although bacterial α diversity increased, microbial network stability decreased in response to Cd, AMF inoculation, and intercropping. The combined treatment also enhanced soil enzyme activity by regulating the relative abundance of dominant or key genera such as Subgroup_6, Rokubacteriales and Pseudarthrobacter. Notably, catalase activity was 97.25 % higher in the combined treatment compared to monoculture without AMF colonization under high Cd conditions. These findings demonstrate the synergistic potential of AMF inoculation and S. nigrum intercropping as a sustainable approach to mitigate Cd contamination in crops while improving soil health in Cd-contaminated environments.

Mature Tiankeng, the negative geological landform surrounded by integral walls as refugia in Karst regions, conserves the unique plant species of karst regions due to isolation from human disturbances and different local microclimates. However, studies exploring the soil biodiversity of mature Tiankengs are lacking entirely. Soil samples were taken from four mature Tiankengs in southwest China, and the species diversity and functions of bacteria and fungi were determined. Generally, the soil nutrient contents, species diversity, and unique species richness of bacteria and fungi were higher in the Tiankeng than in the outside. The microbial functions of human pathogenic, aromatic compounds and plastic degradation associated were higher in Tiankeng than in the outside. Compare to the outside, more bacterial and fungal species in Tiankeng assembled more network modules as well as microbial functions. Results suggested that compared with the outside, rich soil nutrients may contribute the higher microbial diversity and function formed in mature Tiankengs. Since the soil microbial hotspot was defined as soil with small volume and high process rates, we suggest that the theory of soil microbial hotspot may be applied on landscape scales. That is, mature Tiankengs may be treated as the soil microbial hotspots in karst region based on its small volume proportion but high soil nutrients, microbial diversity, and functions. We further suggest identifying the soil microbial hotspots in other landscapes, and this may be key to biological conservation and ecosystem stability with global changes.

With the expansion of the mining industry, environmental pollution from microelements (MP) and red mud (RM) has become a pressing issue. While bioremediation offers a cost-effective and sustainable solution, plant growth in these polluted environments remains difficult. Arundo donax is one of the few plants capable of surviving in RM-affected soils. To identify endophytic fungi that support A. donax in different contaminated environments and to inform future research combining mycorrhizal techniques with hyperaccumulator plants, we conducted a field experiment. The study compared endophytic fungal communities in A. donax grown in uncontaminated, MP soils contaminated with cadmium (Cd), arsenic (As), and lead (Pb), and RM-contaminated soils. Our findings showed that soil nutrient profiles differed by contamination type, with Cd concentrations in MP soils exceeding national pollution standards (GB 15168-2018) and RM soils characterized by high aluminum (Al), iron (Fe), and alkalinity. There were significant differences in the endophytic fungal community structures across the three soil types (p < 0.001). Co-occurrence network analysis revealed that endophytic fungi in MP soils exhibited competitive niche dynamics, whereas fungi in RM soils tended to share niches. Notably, Pleosporales sp., which accounted for 18% of the relative abundance in RM soils, was identified as a dominant and beneficial endophyte, making it a promising candidate for future bioremediation efforts. This study provides valuable insights into the role of endophytic fungi in phytoremediation and highlights their potential as resources for improving plant-microbe interactions in contaminated environments.

Applying microbial fertilizer to assist phytoremediation using high production energy crops is a promising method to improve the removal efficiency of metals contaminated soils. The study was conducted to evaluate the effects of Earth Total Support (ETS, a complex microbial agent) in enhancing the phytoremediation of Arsenic (As) in soils using Arundo donax L, which were grown in mesocosms with As at 20 mg kg-1. The results showed that the addition of ETS significantly increase the biomass of A. donax L by 27.27 %–37.04 %. Additionally, ETS was found to mitigate the adverse effects of As stress on A. donax L by enhancing net photosynthetic rate and transpiration, increasing the activities of superoxide dismutases and peroxidases, and decreased malondialdehyde content. Moreover, the addition of ETS led to a 99.25 % increase in As content in roots and a 7.10 % increase in stems. These findings suggest that ETS agents hold promise in improving the remediation efficiency of low concentration As contaminated soil by significantly increasing the biomass of A. donax and facilitating As extraction.

While karst tiankengs have a higher capacity to act as safe havens for biodiversity in changing climates, little is known about their soil microorganisms. To fill this gap, we investigate the distribution and driving factors of the bacterial community in karst tiankeng systems. There is a significant difference in the soil characteristics between the inside and the outside of a karst tiankeng. At the karst tiankeng considered in this study, the bacterial composition, in terms of the operational taxonomic unit (OTU), was found to be significantly different in different soil samples, taken from diverse sampling sites within the collapsed doline or the external area, and showed a high habitat heterogeneity. The dominant phylum abundances vary with the sampling sites and have their own indicator taxa from phylum to genus. Unlike the primary controlling factors of plant diversity, the microclimate (soil moisture and temperature), soil pH, and slope dominated the distribution of the bacterial community in karst tiankeng systems. Our results firstly showed the distribution characteristics of bacterial communities and then revealed the importance of microhabitats in predicting the microbial distribution in karst tiankeng systems.