Frequent burning causes large losses of carbon from deep soil layers in a temperate savanna
Frequent burning causes large losses of carbon from deep soil layers in a temperate savanna
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DOI：
10.1111/1365-2745.13351
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发表时间：
2020-02
影响因子：
5.5
通讯作者：
A. Pellegrini;K. McLauchlan;S. Hobbie;M. Mack;A. Marcotte;D. Nelson;S. Perakis;P. Reich;K. Whittinghill
中科院分区：
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作者：
A. Pellegrini;K. McLauchlan;S. Hobbie;M. Mack;A. Marcotte;D. Nelson;S. Perakis;P. Reich;K. Whittinghill
全球范围内的火灾活动正在发生戏剧性的变化，对生态系统过程，特别是地下的影响不确定。土壤碳(C)的火灾损失通常被认为主要发生在土壤表层，因为地上生物质的反复燃烧限制了输入到表层土壤的有机质。然而，如果频繁的燃烧减少了根生物量向深层土壤的碳输入，或者通过淋溶和引发刺激了碳的损失，则可能发生深层土壤的碳损失。为了评估火灾对土壤C的影响，我们在温带橡树稀树草原上进行了长达51年的火灾频率控制实验，抽样了12个样地，其中规定的燃烧频率的变化造成了植被结构的梯度，从未焚烧地块的封闭式林冠森林到频繁焚烧地块的开阔林冠稀树草原。土壤碳储量与火烧频率呈非线性相关，其中稀树草原地块在中等火烧频率下达到峰值，最频繁火烧地块土壤碳含量下降。深层土壤的流失量很大，当考虑整个1m的样品而不是只考虑表层0-20 cm时，中等火烧样地与最频繁火烧样地之间的绝对差异增加了一倍以上(全1m层和0-20 cm层的损失分别为98.5mgC/ha[−76%]和42.3mgC/ha[−68%])。与未焚烧的林地相比，最频繁焚烧的样地在全部1米样本中碳含量低65.8mgC/ha(−58%)。上部20 cm以下的根生物量也下降了39%，燃烧更加频繁。同时火灾导致氮的损失和钙、磷的增加表明，燃烧可能会增加氮的限制，并在温带稀树草原的钙和磷循环中发挥关键作用。综合。我们的研究结果表明，森林-稀树草原过渡过程中，火烧引起的土壤碳损失和深层根系生物量的损失可能是调节火烧制度转变对生态系统碳的净影响的关键因素。如果只考虑表层土壤的变化，稀树草原地区随着火灾频率的变化而预测的土壤碳变化可能会低50%。
Fire activity is changing dramatically across the globe, with uncertain effects on ecosystem processes, especially below‐ground. Fire‐driven losses of soil carbon (C) are often assumed to occur primarily in the upper soil layers because the repeated combustion of above‐ground biomass limits organic matter inputs into surface soil. However, C losses from deeper soil may occur if frequent burning reduces root biomass inputs of C into deep soil layers or stimulates losses of C via leaching and priming. To assess the effects of fire on soil C, we sampled 12 plots in a 51‐year‐long fire frequency manipulation experiment in a temperate oak savanna, where variation in prescribed burning frequency has created a gradient in vegetation structure from closed‐canopy forest in unburned plots to open‐canopy savanna in frequently burned plots. Soil C stocks were nonlinearly related to fire frequency, with soil C peaking in savanna plots burned at an intermediate fire frequency and declining in the most frequently burned plots. Losses from deep soil pools were significant, with the absolute difference between intermediately burned plots versus most frequently burned plots more than doubling when the full 1 m sample was considered rather than the top 0–20 cm alone (losses of 98.5 Mg C/ha [−76%] and 42.3 Mg C/ha [−68%] in the full 1 m and 0–20 cm layers respectively). Compared to unburned forested plots, the most frequently burned plots had 65.8 Mg C/ha (−58%) less C in the full 1 m sample. Root biomass below the top 20 cm also declined by 39% with more frequent burning. Concurrent fire‐driven losses of nitrogen and gains in calcium and phosphorus suggest that burning may increase nitrogen limitation and play a key role in the calcium and phosphorus cycles in temperate savannas. Synthesis. Our results illustrate that fire‐driven losses in soil C and root biomass in deep soil layers may be critical factors regulating the net effect of shifting fire regimes on ecosystem C in forest‐savanna transitions. Projected changes in soil C with shifting fire frequencies in savannas may be 50% too low if they only consider changes in the topsoil.