Denitrification is an important component of the nitrogen cycle in soil, returning reactive nitrogen to the atmosphere. Denitrification activity is often concentrated spatially in anoxic microsites and temporally in ephemeral events, which presents a challenge for modelling. The anaerobic fraction of soil volume can be a useful predictor of denitrification in soils. Here, we provide a review of this soil characteristic, its controlling factors, its estimation from basic soil properties and its implementation in current denitrification models. The concept of the anaerobic soil volume and its relationship to denitrification activity has undergone several paradigm shifts that came along with the advent of new oxygen and microstructure mapping techniques. The current understanding is that hotspots of denitrification activity are partially decoupled from air distances in the wet soil matrix and are mainly associated with particulate organic matter (POM) in the form of fresh plant residues or manure. POM fragments harbor large amounts of labile carbon that promote local oxygen consumption and, as a result, these microsites differ in their aeration status from the surrounding soil matrix. Current denitrification models relate the anaerobic soil volume fraction to bulk oxygen concentration in various ways but make little use of microstructure information, such as the distance between POM and air-filled pores. Based on meta-analyses, we derive new empirical relationships to estimate the conditions for the formation of anoxia at the microscale from basic soil properties and we outline how these empirical relationships could be used in the future to improve prediction accuracy of denitrification models at the soil profile scale.

反硝化是土壤氮循环的重要组成部分，将活性氮返回到大气中。反硝化活动通常在空间上集中在缺氧微场所，在时间上集中在短暂事件中，这对建模提出了挑战。土壤体积的厌氧部分可以作为土壤反硝化作用的有用预测因子。在这里，我们回顾了这种土壤特征、其控制因素、根据基本土壤特性的估计及其在当前反硝化模型中的实施。随着新的氧气和微观结构绘图技术的出现，厌氧土壤体积的概念及其与反硝化活动的关系经历了几次范式转变。目前的认识是，反硝化活动的热点部分与湿土壤基质中的空气距离无关，主要与新鲜植物残留物或粪便形式的颗粒有机物（POM）有关。 POM 碎片含有大量的不稳定碳，会促进局部氧气消耗，因此，这些微场地的通气状态与周围土壤基质不同。目前的反硝化模型以各种方式将厌氧土壤体积分数与本体氧浓度联系起来，但很少利用微观结构信息，例如 POM 与充气孔隙之间的距离。基于荟萃分析，我们得出了新的经验关系，以从基本土壤特性估计微尺度缺氧形成的条件，并概述了未来如何使用这些经验关系来提高土壤反硝化模型的预测准确性轮廓比例。