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) 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.

Heavy metal contamination poses severe threats to human health. This study investigated the effects of exogenous silicon (Si) on cadmium (Cd) stress responses and underlying mechanisms in spinach and oilseed rape using hydroponic experiments. Three treatments were applied: control (CK), Cd stress (2 μmol·L-¹ Cd), and Cd+Si (2 μmol·L-¹ Cd + 0.5 mmol·L-¹ Si), with six replicates. Growth parameters, quality indices, antioxidant enzyme activities, and Cd content were analyzed. Si application significantly reduced Cd accumulation compared to Cd-stressed plants. Specifically, Cd content in spinach decreased by 31.6% (shoots) and 12.9% (roots), while in oilseed rape it decreased by 3.3% (shoots) and 28.6% (roots). Alleviating Cd stress, Si increased root length, plant height, and biomass in both species. Concurrently, soluble protein, soluble sugar, and vitamin C contents increased by 55.8%, 8.7%, and 5.7% in spinach and 14.1%, 14.9%, and 7.2% in oilseed rape, respectively. Si application also reduced malondialdehyde (MDA) content, an oxidative stress marker, by 23.8% (stem/leaf) and 17.1% (roots) in spinach, and by 23.5% (stem/leaf) and 20.4% (roots) in oilseed rape. Furthermore, Si modulated antioxidant enzyme activities. In spinach, it decreased superoxide dismutase (SOD) and catalase (CAT) in leaves, and peroxidase (POD), ascorbate peroxidase (APX), and CAT in roots, while increasing POD and APX in leaves and SOD in roots. Oilseed rape exhibited similar Si-induced decreases in leaf/root SOD, POD, and root APX, but showed increased leaf APX and leaf/root CAT activities. In conclusion, Si enhances Cd tolerance in spinach and oilseed rape by differentially modulating antioxidant enzyme activities and reducing oxidative damage, a mechanism not thoroughly elucidated in prior studies for these species. This work provides theoretical insights into Si-mediated Cd detoxification and practical implications for using Si amendments in safe agricultural production on contaminated soils.