Perennially and annually frozen soil carbon differ in their susceptibility to decomposition: Analysis of Subarctic earth hummocks by bioassay, XANES and pyrolysis
Perennially and annually frozen soil carbon differ in their susceptibility to decomposition: Analysis of Subarctic earth hummocks by bioassay, XANES and pyrolysis
复制标题
多年冻土碳和每年冻土碳的分解敏感性不同：通过生物测定、XANES 和热解分析亚北极土丘
DOI：
10.1016/j.soilbio.2013.09.021
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发表时间：
2014
影响因子：
9.7
通讯作者：
E. Gregorich
中科院分区：
文献类型：
--
作者：
A. Gillespie;H. Sanei;A. Diochon;B. Ellert;T. Regier;D. Chevrier;J. Dynes;C. Tarnócai;E. Gregorich
土丘是亚北极地区最常见的图案化地面特征，并且通过冷冻扰动作用（即，通过反复冻融使土壤层混合）在物理上保护土壤有机碳（SOC）免于分解。气候模型预测，亚北极地区将经历不成比例的变暖速度，这可能会加速储存的SOC的分解速度，从而导致CO2的释放增加。我们在这项研究中的目标是表征和发展之间的关系的化学和生物利用度的SOC在地平线的亚北极地球丘。在实验室进行的受控矿化研究中评估了生物降解性。采用X射线吸收近边结构（XANES）光谱法在碳（C）K边处表征土壤有机质（SOM）的化学组成，并采用Rock-Eval热解法测定其热稳定性。矿化生物测定表明，埋藏有机层比表面有机质更不容易受到生物降解，并且与邻近的矿物土壤相比并不明显更容易受到生物降解。通过XANES分析表明，酮的积累埋在有机层，和碳水化合物，酚类和羧酸化合物的损失。这表明酮可用作微生物转化的SOM的生物标志物。与此相反，有机质在常年冻结的矿质土壤（即，在多年冻土层以下），更容易受到生物降解比埋在每年冻结的活动层的矿物和有机土壤。这些视野中的SOM没有显示酮信号，而是显示出较强的酚类含量。热解分析表明，热不稳定部分与C的生物有效性有关，并且在多年冻土中，该部分含有比例较高的含氧官能团。这些结果表明，一个池的不稳定的SOC，相对丰富的酚类化合物，在常年冻土可能容易在气候变暖的分解。未来变暖引起的碳损失，因此，可能主要发生在每年冻结的SOM埋冷扰动，但从常年冻结的C下降的永久冻土表访问。
Earth hummocks are the most common patterned ground feature in the Subarctic region and subduction of organic matter by cryoturbation (i.e., mixing of soil layers by repeated freezing–thawing) physically protects soil organic carbon (SOC) from decomposition. Climate models predict that Subarctic regions will experience disproportionate rates of warming, which may accelerate rates of decomposition of stored SOC and thus cause increased release of CO2. Our objectives in this study were to characterize and develop relationships between the chemistry and bioavailability of SOC in the horizons of Subarctic earth hummocks. Biodegradability was assessed in a controlled mineralization study in the laboratory. The chemical composition of soil organic matter (SOM) was characterized by X-ray absorption near-edge structure (XANES) spectroscopy at the carbon (C)K-edge and its thermal stability was determined by Rock-Eval pyrolysis.The mineralization bioassay showed that buried organic horizons were less susceptible than surface SOM to biodegradation, and not significantly more susceptible than the adjacent mineral soil. Analysis by XANES showed the accumulation of ketones in buried organic horizons, and the loss of carbohydrate, phenolic and carboxylic compounds. This suggests that ketones can be used as biomarkers for microbially transformed SOM. In contrast, SOM in perennially frozen mineral soils (i.e., below the permafrost table), was more susceptible to biodegradation than that in buried mineral and organic soils in the annually frozen active layer. The SOM in these horizons did not show ketone signals but instead showed strong phenolic content. Analysis by pyrolysis indicated that the thermolabile fraction was related to the bioavailability of C, and that in perennially frozen soils, this fraction contained proportionately higher oxygen-containing functional groups. These results point to a pool of labile SOC, relatively rich in phenolic compounds, in perennially frozen soils which may be susceptible to decomposition in a warming climate. Future warming-induced C losses, therefore, may mostly occur not from annually-frozen SOM buried by cryoturbation, but from perennially-frozen C made accessible by falling permafrost table.