Effects of sterilization techniques on chemodenitrification and N2O production in tropical peat soil microcosms

Chemodenitrification – the non-enzymatic process of nitrite reduction – may be an important sink for fixed nitrogen in tropical peatlands with low oxygen, low pH, high organic matter, and variable ferrous iron concentrations. Assessing abiotic reaction pathways is difficult because sterilization/inhibition agents can alter the availability of reactants by changing iron speciation and organic matter composition. We compared six commonly used soil sterilization techniques – γ-irradiation, chloroform, autoclaving, and chemical inhibitors (mercury, zinc, and azide) – for their compatibility with chemodenitrification assays for tropical peatland soils (organic-rich low pH soil from the Eastern Amazon). Out of the six techniques, γ-irradiation resulted in soil treatments with lowest cell viability and denitrification activity, and least effect on pH, iron speciation, and organic matter composition. Nitrite depletion rates in γ-irradiated soils were highly similar to untreated/live soils, whereas other sterilization techniques showed deviations. Chemodenitrification was a dominant process in tropical peatland soils assayed in this study. Abiotic N2O production was low to moderate (3–16 % of converted nitrite), and different sterilization techniques lead to significant variations on production rates due to inherent processes or potential artifacts. Our work represents the first methodological basis for testing the abiotic denitrification and N2O production potential in tropical peatland soil.

化学反硝化（chemodenitrification）——即亚硝酸盐还原的非酶促过程——或为低氧、低pH、高有机质且亚铁浓度多变的热带泥炭地中固定态氮的重要汇。由于灭菌/抑菌剂可通过改变铁形态与有机质组成影响反应物的可获得性，评估非生物反应路径颇具难度。我们针对六种常用土壤灭菌技术——γ射线辐照（γ-irradiation）、氯仿（chloroform）处理、高压蒸汽灭菌（autoclaving），以及汞、锌、叠氮化物三类化学抑制剂——在热带泥炭地土壤（取自亚马逊东部的富有机质低pH土壤）的化学反硝化检测中的兼容性开展了对比实验。六种技术中，γ射线辐照处理的土壤样本细胞活力与反硝化活性最低，且对pH、铁形态及有机质组成的影响最小。经γ射线辐照处理的土壤中亚硝酸盐消耗速率与未处理/活土壤高度相似，而其余灭菌技术则出现显著偏差。本研究检测结果表明，化学反硝化是热带泥炭地土壤中的主导过程。非生物氧化亚氮（N₂O）产生量处于低至中等水平，约为转化亚硝酸盐的3%~16%，且不同灭菌技术会因固有过程或潜在人为误差对产生速率造成显著影响。本研究为检测热带泥炭地土壤的非生物反硝化与氧化亚氮产生潜力提供了首个方法学依据。