University of Helsinki, Department of Forest Sciences, PO Box 27, Latokartanonkaari 7, 00014, Helsinki, Finland.
University of Helsinki, Department of Forest Sciences, PO Box 27, Latokartanonkaari 7, 00014, Helsinki, Finland.
Environ Res. 2020 May;184:109328. doi: 10.1016/j.envres.2020.109328. Epub 2020 Mar 5.
Wildfires strongly regulate carbon (C) cycling and storage in boreal forests and account for almost 10% of global fire C emissions. However, the anticipated effects of climate change on fire regimes may destabilize current C-climate feedbacks and switch the systems to new stability domains. Since most of these forests are located in upland soils where permafrost is widespread, the expected climate warming and drying combined with more active fires may alter the greenhouse gas (GHG) budgets of boreal forests and trigger unprecedented changes in the global C balance. Therefore, a better understanding of the effects of fires on the various spatial and temporal patterns of GHG fluxes of different physical environments (permafrost and nonpermafrost soils) is fundamental to an understanding of the role played by fire in future climate feedbacks. While large amounts of C are released during fires, postfire GHG fluxes play an important role in boreal C budgets over the short and long term. The timescale over which the vegetation cover regenerates seems to drive the recovery of C emissions after both low- and high-severity fires, regardless of fire-induced changes in soil decomposition. In soils underlain by permafrost, fires increase the active layer depth for several years, which may alter the soil dynamics regulating soil GHG exchange. In a scenario of global warming, prolonged exposition of previously immobilized C could result in higher carbon dioxide emission during the early fire succession. However, without knowledge of the contribution of each respiration component combined with assessment of the warming and drying effects on both labile and recalcitrant soil organic matter throughout the soil profile, we cannot advance on the most relevant feedbacks involving fire and permafrost. Fires seem to have either negligible effects on methane (CH) fluxes or a slight increase in CH uptake. However, permafrost thawing driven by climate or fire could turn upland boreal soils into temporary CH sources, depending on how fast the transition from moist to drier soils occurs. Most studies indicate a slight decrease or no significant change in postfire nitrous oxide (NO) fluxes. However, simulations have shown that the temperature sensitivity of denitrification exceeds that of soil respiration; thus, the effects of warming on soil NO emissions may be greater than on C emissions.
野火强烈调节北方森林的碳（C）循环和储存，占全球火灾碳排放量的近 10%。然而，气候变化对火灾的预期影响可能会破坏当前的 C-气候反馈，并使系统转向新的稳定域。由于这些森林大多位于永久冻土广泛分布的高地土壤中，预计的气候变暖、干燥以及更活跃的火灾可能会改变北方森林的温室气体（GHG）预算，并引发全球碳平衡的前所未有的变化。因此，更好地了解火灾对不同物理环境（永久冻土和非永久冻土土壤）下 GHG 通量的各种时空模式的影响，对于理解火灾在未来气候反馈中所起的作用至关重要。虽然大量的 C 在火灾中释放，但火灾后的 GHG 通量在北方森林的碳预算中起着重要的短期和长期作用。植被覆盖恢复的时间尺度似乎决定了低强度和高强度火灾后 C 排放的恢复，而不管火灾引起的土壤分解变化如何。在永久冻土下的土壤中，火灾会使活跃层深度增加数年，这可能会改变调节土壤 GHG 交换的土壤动态。在全球变暖的情况下，以前固定的 C 的长时间暴露可能会导致早期火灾演替过程中更高的二氧化碳排放。然而，如果不了解每个呼吸成分的贡献，并评估升温对整个土壤剖面中易变和顽固的土壤有机质的干燥影响，我们就无法深入探讨与火灾和永久冻土有关的最相关反馈。火灾对甲烷（CH）通量的影响似乎可以忽略不计，或者对 CH 的吸收略有增加。然而，气候或火灾引起的永久冻土融化可能会使高地北方土壤变成临时的 CH 源，这取决于从湿润到干燥土壤的过渡速度有多快。大多数研究表明，火灾后一氧化二氮（NO）通量略有减少或没有明显变化。然而，模拟表明，反硝化的温度敏感性超过了土壤呼吸的温度敏感性；因此，变暖对土壤 NO 排放的影响可能大于对 C 排放的影响。
