Returning crop residues to soil is a central strategy for increasing soil organic carbon (SOC), yet whether biochar-associated persistent free radicals (PFRs) actively regulate the stabilization of residue-derived carbon remains unresolved. Here, graded PFR activities were generated by selective radical quenching while maintaining similar biochar physicochemical properties, and 13C-labeled straw was used to trace residue-derived carbon dynamics in two contrasting agricultural soils. Biochar PFRs enhanced hydroxyl radical (·OH) production in a dose-dependent manner, with the highest-PFR treatment generating 6.1- and 18.1-fold higher ·OH levels than the straw-only control in black soil and fluvo-aquic soil, respectively. This abiotic oxidation accelerated early-stage (0–14 d) straw carbon mineralization without increasing net carbon loss. Instead, it redirected straw-derived carbon toward aromatic intermediates that preferentially accumulated as mineral-associated organic matter (MAOM), increasing the proportion of MAOM carbon derived from straw from 59.4
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
