Both organic matter and iron oxide (FeO) dynamics pose key roles in soil cadmium (Cd) bioavailability. However, the microbially driven transformation of soil organic matter and FeO and their linkages to Cd fractions remain unclear under reductive soil disinfestation (RSD) with different organic sources, which limits our mechanistic understanding of Cd immobilization by RSD. To address this gap, we conducted a 45 day microcosm experiment using a paddy soil contaminated with 22.8 mg/kg Cd. Six treatments were established: untreated control (CK), waterlogged (WF), and RSD-amended soils with 0.7% or 2.1% wheat straw (LWD, HWD) or soybean meal (LSD, HSD). We systematically assessed soil Cd fractionation, organic carbon and FeO concentrations, and bacterial community structure, aiming to clarify differences in Cd immobilization efficiency and the underlying mechanisms between wheat straw and soybean meal. For strongly extractable Cd, wheat straw RSD reduced the soil Cd concentrations from 6.02 mg/kg to 4.32 mg/kg (28.2%), whereas soybean meal RSD achieved a maximum reduction to 2.26 mg/kg (62.5%). Additionally, the soil mobility factor of Cd decreased from 44.6% (CK) to 39.2% (HWD) and 32.5% (HSD), while the distribution index increased from 58.5% (CK) to 62.2% (HWD) and 66.8% (HSD). Notably, the HWD treatment increased soil total organic carbon, humus, and humic acid concentrations by 34.8%, 24.6%, and 28.3%, respectively. Regarding amorphous FeO, their concentrations increased by 19.1% and 33.3% relative to CK. RSD treatments significantly altered soil C/N ratios (5.91–12.5). The higher C/N ratios associated with wheat straw stimulated r-strategist bacteria (e.g., Firmicutes, Bacteroidetes), which promoted carbohydrate degradation and fermentation, thereby enhancing the accumulation of humic substances. In contrast, the lower C/N ratios of soybean meal increased dissolved organic carbon and activated iron-reducing bacteria (FeRB; e.g., Anaeromyxobacter, Clostridium), driving iron reduction and amorphous iron oxide formation. PLS-PM analysis confirmed that wheat straw RSD immobilized Cd primarily through humification, whereas soybean meal RSD relied on FeRB-mediated FeO amorphization. These findings suggest that Cd immobilization in soil under RSD may be regulated by microbially mediated organic matter transformation and iron oxide dynamics, which was affected by organic materials of different C/N ratios.

Soil high‐affinity H ₂ uptake activity can be affected by many factors, including the soil pH. However, the method to determine how pH affects high‐affinity H ₂ uptake activity should be updated. The effect of pH on the biological high‐affinity H ₂ uptake in agricultural soils was compared using three pH buffer systems in the pH 4–8 range. Soil pH was adjusted to the target pH using a buffer system (1 g soil/5 mL pH buffer). Soil slurries were treated with heat (autoclaving) or a chemical (25% v/w of toluene addition, microbial inhibitor) to inhibit biological activity. Sterile pH buffer was used as a negative control. The sterile soil slurry (heat sterilization) was the optimal reference control for measuring biological high‐affinity H ₂ uptake activity. Biological H ₂ uptake activity was resistant to toluene, particularly at extreme pH levels. Overall, soil pH ( p = 0.95) and pH buffer systems ( p = 0.46) did not affect the high‐affinity H ₂ uptake activity in the tested agricultural soils. We provide an updated method to accurately measure the potential high‐affinity H ₂ uptake activity in soil, with an emphasis on the importance of controlling the soil pH.

Soil salinization threatens the cultivation quality of Isatis indigotica , a medicinal plant whose root bioactivity depends on the glucosinolate-derived compound (R,S)-goitrin. Although moderate abiotic stress is widely assumed to stimulate secondary metabolite accumulation, the temporal dynamics of goitrin biosynthesis under salt stress remain poorly understood. This study quantified goitrin content across four NaCl concentrations (100 – 400 mmol/L) and four time points (2, 6, 12, and 24 h). Time-series transcriptome sequencing was performed under 100 mmol/L NaCl. Contrary to prevailing assumptions, goitrin content declined progressively from 2 to 12 h before partially recovering at 24 h, indicating that salt stress transiently suppresses goitrin accumulation rather than promoting it. Transcriptomic analysis identified 7 glucosinolate biosynthesis genes whose expression positively correlated with goitrin content (p < 0.05), and 6 salt stress-responsive genes negatively correlated with goitrin content (p < 0.05). These opposing patterns suggest that stress defense is transiently prioritized over biosynthesis, with partial metabolic recovery as plants adapt. These findings reveal a defense-biosynthesis trade-off mechanism in I. indigotica roots and provide a transcriptomic framework for understanding how abiotic stress reshapes secondary metabolism in medicinal plants. Highlights: Salt stress redirects metabolic resources from goitrin biosynthesis to defense in Isatis indigotica roots, revealing a transcription-driven defense–biosynthesis trade-off. Graphic