The potential for soils to produce nitrous oxide (N₂O) is impacted by past moisture conditions; however, the extent of this impact is not fully understood. We conducted the first review of this, using two literature searches and a meta-analysis. We found 36 studies out of a possible 735 that described experiments where soil moisture conditions had been controlled, such that the impact of antecedent moisture levels could be separated from contemporary moisture levels and attributed to N₂O emissions. Of those studies, 14 (130 data points) used the appropriate experimental design and presented suitable data that could be standardized for the meta-analysis. We found that the degree to which the soil was rewetted and the water filled pore space (WFPS) the soil was brought to were significant explanatory variables (p = < 0.0001). The larger the difference between the dry and wet states of the soil and the higher the WFPS of the soil after rewetting, the larger the hot moment, with an exponential increase once the soil is anaerobic. Substrate availability and fertiliser quantity and type were also important controls on the amount of N₂O emitted during the hot moment (p = < 0.0001). However, controls with a constant WFPS can have the same anaerobicity and substrate concentrations, yet much lower emissions, so we suggest that it is the bioavailability of and how the substrates are utilized by the microbial community, and thus how they are primed by the drought, that is the main causal mechanism. Unfortunately, there is still a large uncertainty regarding how microbial population structure, relative gene abundances and gene expression profiles change according to antecedent dry/wet cycles. We suggest several areas of improvement for future studies and the development of drought-impact curves. These would show the relationship between N₂O emissions and the length of drought (we found no studies that have investigated this) and N₂O emissions and the severity of drought (e.g. the difference between 20% and 40% WFPS).

中文翻译：

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干旱和再湿润对温带和地中海气候中土壤 N2O 排放的影响

土壤产生一氧化二氮 (N ₂ O)的潜力受到过去水分条件的影响；然而，人们尚未完全了解这种影响的程度。我们使用两次文献搜索和一项荟萃分析对此进行了第一次审查。我们在可能的 735 项研究中发现了 36 项研究，这些研究描述了控制土壤水分条件的实验，因此可以将先前水分水平的影响与当代水分水平分开，并将其归因于 N ₂O排放。在这些研究中，有 14 项（130 个数据点）使用了适当的实验设计，并提供了可以为元分析标准化的合适数据。我们发现土壤再润湿的程度和土壤的含水孔隙空间 (WFPS) 是重要的解释变量 ( p = < 0.0001)。土壤干湿状态差异越大，复湿后土壤的 WFPS 越高，热矩越大，一旦土壤厌氧，热矩呈指数增长。基质可用性和肥料数量和类型也是炎热时刻N ₂ O 排放量的重要控制因素（p= < 0.0001)。然而，具有恒定 WFPS 的控制可以具有相同的厌氧性和底物浓度，但排放量要低得多，因此我们建议这是微生物群落的生物利用度和底物如何利用，以及它们如何被干旱引发，这是主要的因果机制。不幸的是，微生物种群结构、相对基因丰度和基因表达谱如何根据先前的干/湿循环而变化，仍然存在很大的不确定性。我们为未来的研究和干旱影响曲线的发展提出了几个改进领域。这些将显示 N ₂ O 排放与干旱持续时间之间的关系（我们没有发现对此进行调查的研究）和 N ₂O 排放和干旱的严重程度（例如，20% 和 40% WFPS 之间的差异）。