Biochar shows promise for remediating coastal salt‑affected soils and supporting potential carbon sequestration, yet its role in the halophyte litter detritusphere, particularly regarding lignin phenols and microbial necromass C (MNC), remains unclear. Herein, we conducted a 370-day microcosm experiment with coastal salt-affected soil from the Yellow River Delta under two moisture conditions (75
Biogas digestate (BD), a nutrient-rich and low-cost carbon source, can be converted into artificial humic acid (AHA) through hydrothermal humification (HTH). However, the process is often constrained by low efficiency and inconsistent product quality. In this study, the effects of different reaction media, including biogas slurry (BS) and deionized water, on the properties of AHA derived from BD at various temperatures (180–260 °C) were investigated. The results showed that BS addition increased both AHA yield and nitrogen content, with a maximum AHA selectivity of 40.16
The anisotropic shrinkage of wood during carbonization critically affects biochar microstructure, but its underlying mechanisms remain unclear. We examined shrinkage behavior in the radial (R) and longitudinal (L) directions in relation to polysaccharide thermal degradation, exchangeable cation species, and cell structure, using ten wood species (five softwoods and five hardwoods) and their cation-exchanged derivatives (H+, Na+, K+, Mg2+, Ca2+). Thermogravimetric and continuous dimensional analyses revealed that the onset of shrinkage in the R-direction is primarily associated with hemicellulose degradation, whereas shrinkage in the L-direction is linked to cellulose degradation and occurs rapidly at temperatures 10–20 °C higher than the derivative thermogravimetric peak, when most cellulose microfibrils have already decomposed. Na+ and K+ lowered shrinkage onset temperatures across most species, whereas in hardwoods, R-direction shrinkage magnitude increased with H+ and Mg2+ substitution. Anatomical differences, particularly in ray parenchyma morphology, explained why hardwoods generally shrank more in the R direction. These results demonstrate that anisotropic shrinkage during wood carbonization is governed by polysaccharide-specific thermal degradation, modulated by exchangeable cation species and anatomical features. Furthermore, directional shrinkage can be predictably tuned through cation control and species selection to optimize biochar microstructure.
The global prevalence of geogenically derived cadmium (Cd) enrichment poses significant risks to agricultural sustainability and food security. Micronutrients such as selenium (Se) usually co-occur with Cd in such regions but exhibit low bioavailability in soils, further causing a “hidden hunger” of nutrient depletion in the food supply chain. Through controlled field experiments, we tested strategically designed biochar-based amendments (clay-, manure-, and iron-enriched variants) at 5–20 t ha−1 on limestone-derived paddy soils to synchronously mitigate Cd mobility while enhancing grain Se accumulation. Biochar amendments decreased grain Cd bioaccumulation by 42.3–85.4
Enhancing dissimilatory nitrate reduction to NH4+–N (DNRA) in agricultural soils provides environmental and agronomic benefits by improving nitrogen retention and reducing nitrogen losses. However, DNRA requires a higher electron input (8 e− per NO3−) than denitrification (5 e− per NO3−), which often results in denitrification dominating nitrate reduction in soils. Although biochar can function as an electron shuttle to facilitate DNRA, it remains unclear whether enhancing its electron-shuttling capacity can further stimulate this nitrogen-conserving pathway. Here, we prepared a biochar with enhanced electron-shuttling capacity by loading redox-active Mn phases onto its surface and evaluated its effects on DNRA in soil. Mn-loaded biochar markedly enhanced electron-shuttling capacity and increased soil DNRA rates by 2.9-fold compared with the control. The electron-shuttling capacity of biochar was positively correlated with surface redox-active Mn content, and both DNRA rates and their contribution to total nitrate reduction increased accordingly. In addition, Mn-loaded biochar increased the relative abundance of nrfA-type bacterial taxa (e.g., Bacteroidota, Ignavibacteriota, and Bacillota) and significantly upregulated nrfA gene expression. These results demonstrate that loading redox-active Mn onto biochar effectively enhances its electron-shuttling function. Reversible Mn redox cycling may facilitate electron transfer, thereby increasing electron availability for nitrate reduction to NH4+–N. Meanwhile, Mn-mediated mobilization of native soil dissolved organic carbon (DOC), without increasing carbon loss, may provide supplementary bioavailable electron donors, collectively promoting DNRA and enhancing soil nitrogen conservation, which was accompanied by lower N2O emissions.
