Quangang Yang

This study evaluated how wheat-straw input modifies the effects of 2% (w/w) wheat straw-derived biochar on Cd availability, soil physicochemical properties, enzyme activities, N transformation and microbial communities during a 49-day incubation. Combining 2% biochar with 6% straw reduced soil-available Cd by 7.14–14.28% relative to the biochar-only treatment, whereas increasing straw input from 6% to 9% did not further improve Cd immobilisation. Compared with straw-only treatments, biochar-amended soils maintained higher pH and lower available Cd, indicating that biochar buffered straw-induced acidification and Cd mobilisation. High carbon input increased β-glucosidase activity and AOB-amoA abundance, which was consistent with enhanced nitrification-related processes and may indirectly influence Cd mobility through soil-pH dynamics. These effects were partly buffered by the alkalinity of biochar. Biochar alone supported the highest microbial alpha diversity, whereas increasing carbon input reduced community richness. The BS6 treatment also maintained relatively high microbial biomass during incubation. Soil pH, mineral N and enzyme activities were associated with a variation in microbial community structure. Overall, moderate wheat-straw input combined with biochar improved Cd immobilisation while maintaining microbial activity and soil biochemical stability, suggesting potential for the remediation of Cd-contaminated agricultural soils.

Yellow River alluvial sandy soil suffers from poor structural stability and low fertility, constraining soybean productivity. We hypothesised that co-applying straw return with an organic–inorganic composite would modify Fe–Al oxide fractions, promote water-stable macroaggregate formation, and thereby improve soybean physiological performance and yield components, with the ternary combination outperforming single or binary regimes. A soil-column experiment was conducted at Shandong Agricultural University Experimental Station, Tai’an, China, using a completely randomised design (n = 3) with six treatments: straw-only control (CK), organic fertiliser (JO), biochar (JB), organic fertiliser+attapulgite (JOA), biochar+attapulgite (JBA), and organic fertiliser+biochar+attapulgite (JOBA). Compared with CK, JOBA increased water-stable macroaggregates (>0.25 mm) by 268.82%, mean weight diameter by 89.88%, and decreased soil bulk density by 19.97%; it also increased catalase activity by 35.74%, pods per plant by 110.34%, seeds per plant by 128.57%, and 100-seed weight by 60.82%. The JOBA showed the greatest overall improvement, reflecting complementary functions among amendments. However, these findings were obtained in a controlled short-term column experiment; field validation and even long-term evaluation are required.

Cadmium (Cd) not only significantly threatens crop growth and food safety but also degrades soil quality and reduces microbial activity. Hydrochar is a carbon-rich material derived from biomass via hydrothermal carbonisation, due to its large specific surface area and abundant surface functional groups, shows great potential for immobilisation remediation of Cd-contaminated soils. We determined hydrochar’s (1) optimal application conditions for soil Cd immobilisation and (2) regulatory effects on foxtail millet growth and development, photosynthesis, antioxidant enzyme activity, resistance gene expression and Cd accumulation. Hydrochar was prepared at two temperatures (240 and 160 °C) and applied at two concentrations (1% and 2%). Hydrochar application reduced soil available Cd by 4.59–10.09% and shifted Cd fractions from acetic acid-extractable to residual forms. Soil organic matter (SOM) and microbial biomass carbon (MBC) increased. Hydrochar application increased plant antioxidant enzyme activity, downregulated SiNRAMP5 and SiHMA2 and upregulated SiHMA3, SiPCS1 and SiMT2. Hydrochar prepared at 240 °C and applied at a 2% concentration exhibited the highest efficiency in immobilising Cd, enhancing plant photosynthesis and antioxidant defence, activating soil microorganisms and increasing SOM and MBC, offering a promising remediation strategy for weakly alkaline Cd-contaminated farmland in northern China.

Passivation is a feasible approach for remediating heavy metal-contaminated soil. However, how passivation stability depends on material type, dosage, and plant cultivar remains unclear. Phosphate rock powder (PR) and bentonite (BN) were applied for passivation at three dosages, and the passivation activity was evaluated on high- and low-Cd-accumulating wheat cultivars. Phosphate rock powder (PR) and BN decreased the available Cd content in the soil by 11.52–26.65% and 11.08–35.00%, and in the wheat grains by 7.28–49.94% and 14.14–57.61%, respectively. PR₃ and BN₃ enhanced wheat yield by 12.77–21.31% and 12.23–18.67%, respectively. The passivation activity of both materials increased with increasing dosage. The optimal ranges for effective, stable Cd passivation were 0.29–0.61 and 3.85–8.46 t ha⁻¹ for PR and BN, respectively. Path analysis revealed that PR acts mainly through increases in soil available phosphorus and associated changes in Cd fractions, whereas BN acts primarily through the soil cation exchange capacity; grain Cd was chiefly associated with reactive Cd fractions. The different Cd accumulation capacities of wheat cultivars affected the passivation effects of PR and BN. The soil of Jimai22 showed significantly lower EXC-Cd and Carb-Cd and significantly higher FeMnOz-Cd than Zhoumai18. Moreover, soil pH was higher for Jimai22 than for Zhoumai18. These results suggest that combining the selection of suitable passivation materials, optimising the dosage and planting low-Cd-accumulating cultivars is an effective strategy for maintaining Cd passivation in weakly alkaline soils.

Storage temperature (ST) and grain moisture content (GMC) critically influence cereal quality during storage. However, their interactive effects, the associations among oxidative indicators, quality components and major volatile organic compounds (VOCs) variations in millet during storage are not fully understood. In this study, foxtail millet was stored for 360 days at three STs (−18 °C, 4 °C and 25 °C) and three GMC levels (11.50%, 12.80% and 14.30%). Changes in oxidative indicators (malondialdehyde [MDA], electrical conductivity [EC] and catalase activity [CAT]) and quality components (crude protein [CP], yellow pigment [YP] and soluble sugar [SS]) were monitored. Viscosity characteristics and VOCs were analysed after storage. Under this study, ST was the primary factor driving the changes in oxidative indicators and quality components during the storage stage. The viscosity characteristics of stored millet are primarily influenced by ST, while the changes in major VOCs are mainly affected by ST, GMC, and their interaction effects. Significant negative correlations were observed between EC or MDA and dodecanenitrile and (E/Z)-4-heptenal, whereas the YP, CP, and SS were significantly positively correlated with both compounds. After day 360, the samples stored at −18 °C with 11.5% GMC exhibited 34.05% lower MDA content and 29.55% lower EC than those stored at 25 °C with 14.3% GMC. The treatment better preserved CAT, SS, YP, viscosity characteristics and major VOCs, including (E/Z)-4-heptenal. These findings provide a scientific basis for optimising storage conditions to maintain the nutritional and sensory quality of foxtail millet.

Constrained by site conditions and water resources, pear tree cultivation faces increasing drought stress. Paecilomyces variotii extract (PVE), a novel biostimulant extracted from wild sea buckthorn root-isolated strains and containing chitin, humic/fulvic acids, and beneficial microbes, has gained attention due to its high activity and efficacy in alleviating plant stresses (e.g., drought). In this study, Pyrus pyrifolia ‘Qiu Yue’ was used as the experimental material, and pot experiments were conducted to examine the drought-mitigating effects of different PVE concentrations. Drought stress was achieved by maintaining soil water content at 35–45% of water holding capacity for 45 days under natural evaporation conditions in rain shelters. The growth status of pear trees, soil enzyme activity, and metabolite levels were analyzed. The results showed that the application of 5 ng/mL PVE promoted pear tree growth, enhanced leaf antioxidant enzyme activity, and improved photosynthetic capacity and soil enzyme activity. Under normal water conditions, the shoot growth length, plant height, stem diameter, and root system activity of the 5 ng/mL PVE group were 31.91%, 12.05%, 3.54%, and 10.94% higher than those of the control group, respectively. Under drought stress, these values increased by 25.12%, 8.87%, 12.21%, and 16.98%, respectively. The addition of 5 ng/mL PVE facilitates trehalose release and upregulates starch-sucrose, glycerophospholipid, and galactose metabolic pathways, thereby potentiating drought stress tolerance in pear trees. However, at 20 ng/mL, reductions were observed in pear tree growth indicators, leaf antioxidant enzyme activity, soil enzyme activity, and trehalose content in root exudates compared to the 5 ng/mL PVE treatment. Overall, 5 ng/mL PVE effectively promotes pear tree growth and enhances drought resistance, making it suitable for broader use in pear cultivation practices.

Cadmium (Cd) contamination poses severe threats to agricultural productivity and ecosystem health. Biochar has shown promise in immobilizing Cd and enhancing microbial functions, yet its pH-dependent mechanisms remain underexplored. This study aimed to elucidate pH-dependent variations in biochar-mediated cadmium (Cd) immobilization efficiency, nitrification activity, and bacterial community diversity across soils of contrasting pH levels, with mechanistic insights into the synergistic interplay between biochar properties and soil pH. Real-time quantitative PCR (qPCR) and high-throughput sequencing were used to investigate the effects of a 1% (w/w) biochar amendment on ammonia-oxidizing microorganism abundance and microbial diversity in neutral Shandong soil (SD, pH 7.46) and acidic Yunnan soil (YN, pH 5.88). In neutral SD soil, available Cd decreased from 0.22 mg kg⁻¹ (day 0) to 0.1 mg kg⁻¹ (day 56) and stabilized, accompanied by insignificant changes in ammonia-oxidizing bacteria (AOB) abundance. However, nitrification activity was enhanced through the enrichment of Nitrospira (nitrite-oxidizing bacteria within Nitrospirales and Nitrospiraceae). In acidic YN soil, biochar reduced available Cd by 53.37% over 56 days, concurrent with a 34.28% increase in AOB amoA gene abundance (predominantly Nitrosomonadales), driving pH-dependent nitrification enhancement. These findings demonstrated that biochar efficacy was critically modulated by soil pH; the acidic soils require higher biochar dosages (>1% w/w, adjusted to local soil properties and agronomic conditions) for optimal Cd immobilization. Meanwhile, pH-specific nitrifier taxa (Nitrosomonadales in acidic vs. Nitrospira in neutral soils) underpinned biochar-induced nitrification dynamics. The study provided a mechanistic framework for tailoring biochar remediation strategies to soil pH gradients, emphasizing the synergistic regulation of Cd immobilization and microbial nitrogen cycling.