Production and reduction of nitrous oxide (N₂O) by soil denitrifiers influence atmospheric concentrations of this potent greenhouse gas. Accurate projections of the net N₂O flux have three key uncertainties: (1) short- vs. long-term responses to warming, (2) interactions among soil horizons, and (3) temperature responses of different steps in the denitrification pathway. We addressed these uncertainties by sampling soil from a boreal forest climate transect encompassing a 5.2 ^∘C difference in the mean annual temperature and incubating the soil horizons in isolation and together at three ecologically relevant temperatures in conditions that promote denitrification. Both short-term exposure to warmer temperatures and long-term exposure to a warmer climate increased N₂O emissions from organic and mineral soils; an isotopic tracer suggested that an increase in N₂O production was more important than a decline in N₂O reduction. Short-term warming promoted the reduction of organic horizon-derived N₂O by mineral soil when these horizons were incubated together. The abundance of nirS (a precursor gene for N₂O production) was not sensitive to temperature, whereas that of nosZ clade I (a gene for N₂O reduction) decreased with short-term warming in both horizons and was higher from a warmer climate. These results suggest a decoupling of gene abundance and process rates in these soils that differs across horizons and timescales. In spite of these variations, our results suggest a consistent, positive response of denitrifier-mediated net N₂O efflux rates to temperature across timescales in these boreal forests. Our work also highlights the importance of understanding cross-horizon N₂O fluxes for developing a predictive understanding of net N₂O efflux from soils.

中文翻译：

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土壤反硝化器净N ₂ O外排率，剖面内N ₂ O动力学和微生物遗传潜力的短期和长期温度响应

土壤反硝化剂的产生和一氧化二氮（N ₂ O）的还原会影响这种有效温室气体的大气浓度。N ₂ O净净通量的准确预测 具有三个主要不确定性：（1）对变暖的短期或长期响应；（2）土壤层位之间的相互作用；（3）反硝化途径中不同步骤的温度响应。我们通过从北方针叶林气候断面包含一个5.2采样土壤处理这些不确定性 ^∘ Ç年平均温度的差异，以及在促进反硝化的条件下，在三个与生态相关的温度下，一起以及在三个与生态相关的温度下共同培育土壤层。短期暴露于较温暖的温度和长期暴露于较温暖的气候都会增加有机和矿物土壤中的N ₂ O排放；同位素示踪剂表明，N ₂ O产生的增加比N ₂ O减少的减少更为重要。将这些层位一起孵育时，短期变暖促进了矿物土壤中有机层位的N ₂ O的减少。大量的NIRS（产生N ₂ O的前体基因）对温度不敏感，而nosZ进化枝I（减少N ₂ O的基因）的温度在短期内都随短期变暖而降低，而在气候变暖时则更高。这些结果表明，这些土壤中的基因丰度和加工速率之间存在脱钩，这在不同的水平和时间尺度上是不同的。尽管存在这些变化，但我们的结果表明，在这些北方森林中，反硝化剂介导的净N ₂ O外排率对不同时间的温度具有一致的正响应。我们的工作还强调了理解跨水平N ₂ O的重要性 通量用于发展对土壤中净N ₂ O外流的预测性理解。