Xiaolin Liao

Biochar amendment is widely used to enhance soil carbon storage and regulate greenhouse gas emissions, but field evidence from forest plantations remains limited. This 1.5-year field study investigated the responses of soil greenhouse gas (GHG) emissions and carbon storage to rice husk biochar applied at 15 t ha⁻¹ (LB) and 30 t ha⁻¹ (HB) in a subtropical poplar plantation. At 3.0 m from the tree stem, biochar did not significantly affect cumulative N₂O emissions but significantly increased cumulative CO₂ emissions and reduced CH₄ emissions by 49.36% (LB) and 21.80% (HB), resulting in no significant change in non-CO₂ GHG-based global warming potential. In contrast, biochar significantly enhanced measured soil organic carbon (SOC) storage in several soil layers, especially in the 0–20 cm layer, and increased mineral-associated organic carbon (MAOC) while decreasing the POC: MAOC ratio, indicating a greater allocation of SOC towards more recalcitrant fractions. However, when carbon storage was integrated over the 0–100 cm profile, a significant increase was observed only under the high biochar rate at D1. These findings suggest that biochar can enhance carbon storage in poplar plantation soils, although its GHG mitigation effect is limited and gas-specific. Additional measurements in biochar-amended plots showed higher N₂O emissions closer to the tree stem (1.5 m), suggesting that future studies should use full-factorial treatment × distance designs to evaluate tree-proximity effects on biochar responses in plantation soils.

Biochar is increasingly promoted as a strategy for mitigating soil nitrous oxide (N ₂ O) emissions, yet its effect on the temperature sensitivity (Q ₁₀ ) of N ₂ O emissions remains poorly understood. In this study, short-term incubation experiments were conducted using two contrasting soils (agricultural and forest soils) amended with two biochar types (wood- and rice husk-derived) at three application rates (0, 1%, and 3%) under three temperatures (10 °C, 20 °C, 30 °C). We investigated how biochar alters Q ₁₀ of N ₂ O emissions and explored the underlying mechanisms. Results showed that cumulative N ₂ O emissions increased with temperature in both soils, with higher Q ₁₀ values in forest soils (1.63–2.84) than in agricultural soils (1.13–1.63). Only high-rate wood biochar (WH) significantly changed Q ₁₀ , decreasing it in agricultural soils but increasing it in forest soils. In agricultural soils, WH strongly reduced NO ₃ ⁻ –N availability and minimized its temperature response, intensifying substrate limitation and lowering Q ₁₀ . In forest soils, biochar accelerated the decline of NH ₄ ⁺ –N and slowed the increase of NO ₃ ⁻ –N with temperature, suggesting tighter coupling between nitrification and nitrate-consuming processes. Although WH and high rate rice-husk biochar showed the smallest NO ₃ ⁻ -temperature slopes, the unique properties of WH (e.g., low ash content, higher aromaticity, and larger pore size) may have promoted short-term NO ₃ ⁻ retention, thereby strengthening temperature-coupled nitrification–denitrification turnover, which likely contributed to the higher Q ₁₀ observed under WH. Partial least squares path modeling (PLS-PM) confirmed that temperature exerted stronger total effects on N ₂ O emissions than biochar through changes in substrate availability, pH, and functional genes, while biochar acted as a secondary modulator. Overall, biochar regulated N ₂ O Q ₁₀ through soil-specific pathways, highlighting the need for soil-specific biochar application strategies under future climate change scenarios. Graphical Abstract