Data from: Effect of soil pH increase by biochar on NO, N2O and N2 production during denitrification in acid soils

Biochar (BC) application to soil suppresses emission of nitrous- (N2O) and nitric oxide (NO), but the mechanisms are unclear. One of the most prominent features of BC is its alkalizing effect in soils, which may affect denitrification and its product stoichiometry directly or indirectly. We conducted laboratory experiments with anoxic slurries of acid Acrisols from Indonesia and Zambia and two contrasting BCs produced locally from rice husk and cacao shell. Dose-dependent responses of denitrification and gaseous products (NO, N2O and N2) were assessed by high-resolution gas kinetics and related to the alkalizing effect of the BCs. To delineate the pH effect from other BC effects, we removed part of the alkalinity by leaching the BCs with water and acid prior to incubation. Uncharred cacao shell and sodium hydroxide (NaOH) were also included in the study. The untreated BCs suppressed N2O and NO and increased N2 production during denitrification, irrespective of the effect on denitrification rate. The extent of N2O and NO suppression was dose-dependent and increased with the alkalizing effect of the two BC types, which was strongest for cacao shell BC. Acid leaching of BC, which decreased its alkalizing effect, reduced or eliminated the ability of BC to suppress N2O and NO net production. Just like untreated BCs, NaOH reduced net production of N2O and NO while increasing that of N2. This confirms the importance of altered soil pH for denitrification product stoichiometry. Addition of uncharred cacao shell stimulated denitrification strongly due to availability of labile carbon but only minor effects on the product stoichiometry of denitrification were found, in accordance with its modest effect on soil pH. Our study indicates that stimulation of denitrification was mainly due to increases in labile carbon whereas change in product stoichiometry was mainly due to a change in soil pH.将生物炭（Biochar, BC）施入土壤可抑制一氧化二氮（N₂O）与一氧化氮（NO）的排放，但其内在作用机制尚未明确。生物炭最显著的特性之一是其对土壤的碱化效应，该效应可直接或间接调控反硝化作用（denitrification）及其产物化学计量比（product stoichiometry）。 本研究以印度尼西亚与赞比亚的酸性强淋溶土（Acrisols）厌氧泥浆（anoxic slurries）为实验基质，采用本地制备的稻壳（rice husk）基与可可壳（cacao shell）基两种性质差异显著的生物炭开展室内培养实验。通过高分辨率气体动力学分析，评估反硝化作用及其气态产物（NO、N₂O与N₂）的剂量依赖性响应，并将其与生物炭的碱化效应相关联。为区分土壤pH变化与生物炭的其他作用效应，我们在培养前通过水淋洗与酸淋洗去除了部分生物炭的碱度。本研究同时设置了未炭化可可壳与氢氧化钠（sodium hydroxide, NaOH）对照组。 未处理的生物炭可在反硝化过程中抑制N₂O与NO的产生，并提升N₂的生成量，该效应不受反硝化速率变化的影响。N₂O与NO的抑制程度呈剂量依赖性，且随两种生物炭的碱化效应增强而升高，其中可可壳基生物炭的碱化效应最强。对生物炭进行酸淋洗可降低其碱化能力，进而削弱甚至完全消除生物炭抑制N₂O与NO净生成的能力。 与未处理的生物炭类似，氢氧化钠（NaOH）同样可降低N₂O与NO的净生成量，同时提升N₂的生成量。这一结果证实了土壤pH改变对反硝化产物化学计量比的重要调控作用。 未炭化可可壳因可为微生物提供活性碳（labile carbon）底物而显著促进反硝化作用，但对反硝化产物化学计量比的影响微弱，这与其对土壤pH的小幅调控作用相符。 本研究表明，反硝化作用的促进主要源于活性碳含量的提升，而反硝化产物化学计量比的改变则主要由土壤pH变化所致。