Dynamics of Charcoal Alteration in a Tropical Biome: A Biochar-Based Study
Dynamics of Charcoal Alteration in a Tropical Biome: A Biochar-Based Study
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DOI：
10.3389/feart.2018.00061
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发表时间：
2018-06-04
影响因子：
2.9
通讯作者：
Shen, Licheng
中科院分区：
文献类型：
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作者：
Ascough, Philippa L.;Bird, Michael I.;Shen, Licheng
热解碳（PyC）是生物质或化石燃料不完全燃烧产生的多环芳烃残留物。人们越来越认识到，由于116-385 Tg C年的生产率以及全球碳库中PyC储量的规模和普遍性，PyC构成了碳预算的重要组成部分。至少有一部分PyC以高度挥发性的化学形式存在，这提高了通过用“生物炭”改良土壤来长期固碳的前景，生物炭通常是为了制造一种特别挥发性的PyC形式而生产的。然而，越来越多的证据表明，一些热解碳，包括生物炭，可以在物理和化学上改变和降解暴露于环境中超过每年的时间尺度，但缺乏有关的信息themechanisms和决定因素的退化。在这里，我们研究了三个主要因素：生产温度、原料成分和材料所暴露的环境特征（例如，pH值，有机物组成，氧气供应）通过分析生物炭样品的垃圾袋实验之前和之后，在澳大利亚东北部的热带雨林长达一年的实地研究。我们发现，非木质纤维素原料具有较低的芳香性，加上较低的O/C和H/C的比例，对于一个给定的温度，因此较低的固碳潜力。样品改变的速率取决于生产温度;然而，即使在最高温度的样品中，观察到半不稳定芳族碳组分的损失超过1年。C-13-MAS-NMR测量的结果表明，芳香族结构的直接氧化可能比生物炭（作为PyC的子集）的环境改变中的羧化更重要。即使在本研究的相对较短的时间范围内，沉积环境对生物炭蚀变也有明显的影响，因为暴露在土壤表面的最含氧材料的变化最为广泛。这很可能是矿物质进入和土壤微生物群定植的结果。因此，氧气的可用性和物理或化学保护，从阳光和/或雨水是至关重要的，在确定这种材料的蚀变轨迹。
Pyrogenic carbon (PyC) is a polyaromatic residue of the incomplete combustion of biomass or fossil fuels. There is a growing recognition that PyC forms an important part of carbon budgets, due to production rates of 116-385 Tg C yr, and the size and ubiquity of PyC stocks in global carbon reservoirs. At least a proportion of PyC exists in a highly recalcitrant chemical form, raising the prospect of long-term carbon sequestration through soil amendment with "biochar," which is generally produced with the aim of making a particularly recalcitrant form of PyC. However, there is growing evidence that some PyC, including biochar, can be both physically and chemically altered and degraded upon exposure to the environment over annual timescales, yet there is a lack of information concerning themechanisms and determining factors of degradation. Here, we investigate three main factors; production temperature, feedstock composition, and the characteristics of the environment to which the material is exposed (e.g., pH, organic matter composition, oxygen availability) by analysis of biochar samples in a litterbag experiment before and after a year-long field study in the tropical rainforests of northeast Australia. We find that non-lignocellulosic feedstock has lower aromaticity, plus lower O/C and H/C ratios for a given temperature, and consequently lower carbon sequestration potential. The rate at which samples are altered is production temperature-dependant; however even in the highest temperature samples loss of the semi-labile aromatic carbon component is observed over 1 year. The results of C-13-MAS-NMRmeasurements suggest that direct oxygenation of aromatic structures may be even more important than carboxylation in environmental alteration of biochar (as a subset of PyC). There is a clear effect of depositional environment on biochar alteration even after the relatively short timescale of this study, as changes are most extensive in the most oxygenated material that was exposed on the soil surface. This is most likely the result of mineral ingress and colonization by soil microbiota. Consequently, oxygen availability and physical or chemical protection from sunlight and/or rainwater is vital in determining the alteration trajectory of this material.