Heavy metal in soil have been shown to be toxic with high concentrations and acts as selective pressure on both bacterial metal and antibiotic resistance determinants, posing a serious risk to public health. In cadmium (Cd) and zinc (Zn) contaminated soil, chitosan (Chi) and Trichoderma harzianum (Tri) were applied alone and in combination to assist phytoremediation by Amaranthus hypochondriacus L. Prevalence of antibiotic and metal resistance genes (ARGs and MRGs) in the soil was also evaluated using metagenomic approach. Results indicated that the phytoremediation of Cd and Zn contaminated soil was promoted by Chi, and Tri further reinforced this effect, along with the increased availability of Cd and Zn in soil. Meanwhile, combination of Chi and Tri enhanced the prevalence of ARGs (e.g., multidrug and β-lactam resistance genes) and maintained a high level of MRGs (e.g., chromium, copper) in soil. Soil available Zn and Cd fractions were the main factors contributing to ARGs profile by co-selection, while boosted bacterial hosts (e.g., Mitsuaria, Solirubrobacter, Ramlibacter) contributed to prevalence of most MRGs (e.g., Cd). These findings indicate the potential risk of ARGs and MRGs propagation in phytoremediation of metal contaminated soils assisted by organic and biological agents.

Soil disinfestation has been widely used as an effective strategy to improve soil health and crop yield by suppression of soil-borne plant pathogens, but its effect on soil organic carbon (SOC), a crucial factor linked to climate change, remains unknown. A microcosm trial was conducted to evaluate microbial residue carbon (MRC) and its contribution to SOC under chemical soil disinfestation (CSD) with quicklime (QL) and chloropicrin (CP), as well as anaerobic soil disinfestation (ASD) with maize straw (MASD) and soybean straw (SASD). The SOC concentrations were increased by both CSD and ASD. Also, total SOC-normalized MRC concentration was enhanced, with a considerable increase in soil bacterial and fungal MRC, particularly evident under CP and SASD treatment. Due to broad-spectrum biocidal activities, decreased SOC-normalized microbial biomass carbon (MBC) was consistent with the reductions in bacterial and fungal phospholipid fatty acids (PLFAs), consequently increasing MRC accumulation under CSD. Similarly, ASD decreased fungal PLFAs while shifting bacterial PLFAs from aerobic to anaerobic taxa or from gram-negative to -positive taxa, both of which contributed to both MBC and MRC buildup. Collectively, the findings demonstrate that ASD can efficiently increase SOC concentration, with distinct mechanisms underlying MRC generation when compared to traditional CSD.

Reductive soil disinfestation (RSD) significantly alters soil characteristics, yet its combined effects with bacterial inoculation on subsequent rhizospheric microbial community composition remains poorly understood. To address this knowledge gap, we investigated the effects of RSD and endophytic Brevibacillus laterosporus inoculation on the composition, network, and predicted function of peanut rhizospheric bacteria and fungi. Our results demonstrated that RSD and B. laterosporus inoculation substantially increased rhizospheric bacterial diversity while reducing fungal diversity. Specifically, B. laterosporus-enhanced RSD significantly reshaped the bacterial community, resulting in increased relative abundances of Chloroflexi, Desulfobacterota, and Myxococcota while decreasing those of Firmicutes, Gemmatimonadota, and Acidobacteriota. The fungal community exhibited a more consistent response to RSD and B. laterosporus amendment, with reduced proportions of Ascomycota and Gemmatimonadota but an increase in Chytridiomycota. Network analysis revealed that B. laterosporus inoculation and RSD enhanced the bacterial species complexity and keystone taxa. Furthermore, canonical correspondence analysis indicated strong associations between the soil bacterial community and soil properties, including Eh, EC, NO₃⁻-N, and SOC. Our findings highlight that the shifts in bacterial taxa induced by B. laterosporus inoculation and RSD, particularly the keystone taxa identified in the network, may contribute to the suppression of soil-borne pathogens. Overall, this study provides a novel insight into the shifts in rhizospheric bacterial and fungal communities and their ecological functions after bacteria inoculation and RSD treatment.

Reductive soil disinfestation (RSD) is a promising strategy for mitigating soil degradation and enhancing soil health. While soil organic carbon (SOC) is crucial for soil fertility and climate regulation, the mechanisms underlying its stabilization via plant lignin and microbial humus in the RSD process remain elusive. Using a microcosm experiment, we investigated SOC dynamics by quantifying plant-derived (lignin phenols) and microbial-derived (amino sugars) C during RSD at key stages: initial (2 h), anaerobic (14 and 28 days), and aerobic (35 days). Concurrently, soil properties, microbial PLFA, and enzymatic activity were analyzed to elucidate underlying mechanisms. Over the initial 14 days, plant-derived C increased sharply by 61% before declining, yet still showed a 22% increase by the end of the RSD (35 days), a trend mirrored by bacterial-derived C. In contrast, fungal-derived C initially accumulated rapidly with a significant increase of 43%, then stabilized, and its proportion (21.63%) surpassed that of bacterial-derived C (5.56%). Over time, plant- (25.01% to 19.76%) and bacterial-derived C (7.81% to 5.56%) contributions to decreases in SOC, while fungal-derived C (about 21%) remained stable after day 14. This pattern is likely attributable to the initial anaerobic conditions, which caused a massive die-off of fungi and aerobic bacteria that utilize lignin and necromass, resulting in significant accumulation of both plant- and microbial-derived C. Subsequently, the proliferation of anaerobic bacteria consumed these plant- and bacterial-derived C sources in the soil, leading to their eventual decline. Key drivers of plant-derived C included soil pH, living fungi/bacteria, and β-1,4-glucosidase activity, whereas microbial-derived C depended on total nitrogen and living fungi. Our findings demonstrate that early SOC accumulation under RSD is driven by combined plant lignin and microbial necromass inputs, while fungal necromass becomes pivotal for long-term SOC stabilization, shaped by both abiotic and biotic factors.