Selective preservation of pyrogenic carbon across soil organic matter fractions and its influence on calculations of carbon mean residence times
Selective preservation of pyrogenic carbon across soil organic matter fractions and its influence on calculations of carbon mean residence times
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DOI：
10.1016/j.geoderma.2019.07.024
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发表时间：
2019-11
期刊：
影响因子：
6.1
通讯作者：
J. Lavallee;R. Conant;M. Haddix;R. Follett;M. Bird;E. Paul
中科院分区：
文献类型：
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作者：
J. Lavallee;R. Conant;M. Haddix;R. Follett;M. Bird;E. Paul
长期以来，人们一直认为土壤有机碳（SOC）的难降解性控制着其稳定性和持久性，但现在已经转变为有机碳对微生物的物理难接近性起着主导作用。这种模式的转变已经促进了分析技术，隔离SOC到物理馏分保护分解不同的机制。这些分数和SOC年龄之间的相关性加强了SOC不可达性的重视。热原C（PyC;也称为木炭或黑碳），已知其已被火热改变，含有高度不稳定的成分，其分解非常缓慢，并且可以代表这种范式转变的例外。我们采用氢热解量化的贡献PyC的总SOC的土壤组分从三个长期的农业实验，土地利用转换，导致减少SOC。我们表明，所有的土壤组分含有PyC和高达五分之一的SOC的土壤组分被认为具有低访问性是由PyC。无论它所在的土壤组分，热解碳是相对不受影响的土地利用转换相比，生物碳（有机碳不改变火），这表明，选择性保护，而不是物理保护，是主要的机制限制热解碳分解在这些网站。我们占PyC的C平均停留时间（MRT）的计算中使用的PyC和SOC之间的稳定C同位素比值的差异。虽然结果不同的网站和土壤组分，MRT生物源C一般短于总SOC。基于这些结果，PyC分解是由不同的机制比生物源C控制，这应该考虑在土壤C动态的研究。此外，仅基于物理分馏的方法可能过于强调不可达性对SOC长期持续性的作用。
The long-standing perspective that recalcitrance of soil organic carbon (SOC) controls its stability and persistence has shifted to one in which physical inaccessibility of SOC to microorganisms plays a predominant role. This paradigm shift has been facilitated by analytical techniques that isolate SOC into physical fractions protected from decomposers by different mechanisms. The correlation between these fractions and SOC age has reinforced the emphasis of SOC inaccessibility. Pyrogenic C (PyC; also called charcoal or black carbon), which has been thermally altered by fire, is known to contain highly recalcitrant components that decompose very slowly and could represent an exception to this paradigm shift. We employed hydrogen pyrolysis to quantify the contribution of PyC to total SOC across soil fractions from three long-term agricultural experiments with land use conversions that caused reductions in SOC. We show that all soil fractions contain PyC and up to one-fifth of SOC in soil fractions considered to have low accessibility is comprised of PyC. Regardless of the soil fraction in which it was located, PyC was relatively unaffected by land use conversion compared to biogenic C (organic C not altered by fire), which suggests that selective preservation, rather than physical protection, is the dominant mechanism limiting PyC decomposition in these sites. We accounted for PyC in calculations of C mean residence times (MRTs) using differences in stable C isotope ratios between PyC and SOC. Though results varied by site and soil fraction, MRTs for biogenic C were generally shorter than for total SOC. Based on these results, PyC decomposition is controlled by a different mechanism than biogenic C, and this should be considered in studies of soil C dynamics. In addition, methods based on physical fractionation alone may place too great an emphasis on the role of inaccessibility for long-term SOC persistence.