This study aimed to explore the effects of biochar on pulse CO₂ and N₂O emissions and N cycling microbial functional genes after a short-term drought through a soil incubation experiment. Soil samples were collected in a macadamia orchard where biochar was applied 5 years prior to the incubation. Samples were wetted after being subjected to short-term (2-month) drought conditions. Samples were analysed for gas emissions (N₂O and CO₂), available NH₄⁺-N, and NO₃⁻-N, water soluble organic carbon (WSOC), water soluble total N (WSTN), and N cycling microbial gene abundance for a period of 21 days post-drought. Soil CO₂ emissions were significantly higher in the drought-affected soil with no biochar than in the control soil with no biochar. No effect of biochar was detected on CO₂ emissions for drought-affected soil. Available labile C (WSOC) in drought-affected soil was higher than in soils not subjected to drought, regardless of the presence of biochar. Therefore, C loss after adding water could be explained by the release of labile C accumulated during drought. Drought-affected soil with biochar did not influence N₂O emissions compared with control soil subject to drought. In soils not subjected to drought, biochar had higher NO₃⁻-N than the soil without biochar at day 7 post-drought, which could partly be explained by increased soil ammonia-oxidising bacteria (AOB) gene abundance. Our study suggested that a pulse C loss was more likely to occur post-drought whereas pulse N loss through N₂O emission was not evident regardless of biochar application particularly within first day after being rewetted. Our study highlights the pulse effects of drought on GHG emissions from the soil after being wetted.

本研究旨在通过土壤孵化实验探讨生物炭对短期干旱后脉冲CO ₂和N ₂ O排放以及氮循环微生物功能基因的影响。在澳洲坚果园收集土壤样品，在孵化前 5 年在那里施用生物炭。样品在经历短期（2 个月）干旱条件后被弄湿。分析样品的气体排放量（N ₂ O 和 CO ₂）、可用 NH ₄ ⁺ -N 和 NO ₃ ^- -N、水溶性有机碳 (WSOC)、水溶性总 N (WSTN) 和 N 循环微生物基因干旱后 21 天的丰度。土壤 CO ₂不含生物炭的干旱影响土壤的排放量显着高于不含生物炭的对照土壤。对于受干旱影响的土壤，未检测到生物炭对 CO ₂排放的影响。无论是否存在生物炭，受干旱影响的土壤中的有效不稳定碳 (WSOC) 都高于未受干旱影响的土壤。因此，加水后的 C 损失可以用干旱期间积累的不稳定 C 的释放来解释。与受干旱影响的对照土壤相比，受干旱影响的生物炭土壤不影响 N ₂ O 排放。在未受干旱影响的土壤中，生物炭具有较高的 NO ₃ ^--N 在干旱后第 7 天与没有生物炭的土壤相比，部分原因是土壤氨氧化细菌 (AOB) 基因丰度增加。我们的研究表明，干旱后更可能发生脉冲 C 损失，而通过 N ₂ O 排放的脉冲 N 损失并不明显，无论生物炭应用如何，特别是在重新润湿后的第一天。我们的研究强调了干旱对土壤润湿后温室气体排放的脉冲效应。