From energy to (soil organic) matter
From energy to (soil organic) matter
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从能量到（土壤有机）物质
DOI：
10.1111/gcb.16071
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发表时间：
2022-01-17
影响因子：
11.6
通讯作者：
Kuzyakov, Yakov
中科院分区：
文献类型：
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作者：
Gunina, Anna;Kuzyakov, Yakov
在这篇概念论文中，我们提出了一种关于土壤有机质(SOM)形成的新观点：微生物将进入土壤的大部分有机物作为能量而不是碳(C)的来源，而SOM作为残留的副产品积累，因为微生物在其分解过程中的能量投入超过了能量获得。在分解初期，剩余凋落物中C(NOSC)的标称氧化态降低，能量含量增加。这反映了具有正性和中性NOSC(羧酸、糖、一些氨基酸)的可用化合物的快速矿化。因此，剩余化合物的NOSC降至-0.3个单位，氧化速率降低，这是由于芳香族和脂肪族化合物(稍后被水解)的残留相对积累和坏死体的埋藏。最终，未完全分解的植物残留物每单位碳的能量将比最初的凋落物多1%-2.5%。凋落物分解的实验数据支持了氧化后大范围有机物的能量密度在每个NOSC单位中线性下降106kJ·mol(-1)C的说法。富含能量的还原物质(脂类、芳香烃、某些氨基酸、氨基糖)的优先循环以及氧化化合物(羧酸)的微生物降解也能使土壤有机质变得富含能量。尽管SOM的能量含量较高，但SOM中储存的能量利用率低于枯枝落叶。这解释了为什么SOM没有完全矿化(热力学上不利)，特别是在缺乏植物C提供新能量的情况下(例如，在裸露的土壤中)。由于土壤有机质中的养分含量比枯枝落叶高2-5倍，凋落物中的能量会激活分解者来利用土壤有机质中储存的养分(引发效应的主要生态功能)。这导致SOM中只有0.4%-5%的年(-1)凋落物来源的C被隔离，而SOM(-1)储存了总凋落物来源能量的1%-10%。因此，光合作用捕获的能量是微生物利用有机质的主要原因，而有机质只是营养储存的残余副产品和能量流动的媒介。
In this concept paper, we propose a new view on soil organic matter (SOM) formation: microorganisms use most of the organics entering the soil as energy rather than as a source of carbon (C), while SOM accumulates as a residual by-product because the microbial energy investment in its decomposition exceeds the energy gain. During the initial stages of decomposition, the nominal oxidation state of C (NOSC) in remaining litter decreases, and the energy content increases. This reflects the rapid mineralization of available compounds with positive and neutral NOSC (carboxylic acids, sugars, some amino acids). Consequently, the NOSC of the remaining compounds drops to -0.3 units, and the oxidation rate decreases due to the residual relative accumulation of aromatic and aliphatic compounds (which are hydrolized later) and entombment of the necromass. Ultimately, incompletely decomposed plant residues will have 1%-2.5% more energy per C unit than the initial litter. The linear decrease in energy density of a broad range of organic substances by 106 kJ mol(-1) C per NOSC unit upon oxidation is supported by experimental data on litter decomposition. Preferential recycling of energy-rich reduced (lipids, aromatics, certain amino acids, amino sugars) and the microbial degradation of oxidized compounds (carboxylic acids) also energetically enrich SOM. Despite the high energy content, the availability of energy stored in SOM is lower than in litter. This explains why SOM is not fully mineralized (thermodynamically unfavorable), especially in the absence of plant C to provide new energy (e.g., in bare soil). Energy from litter activates decomposers to mine nutrients stored in SOM (the main ecological function of priming effects) because the nutrient content in SOM is 2-5 times higher than that of litter. This results in only 0.4%-5% year(-1) of litter-derived C being sequestered in SOM, whereas SOM stores 1%-10% year(-1) of the total litter-derived energy. Thus, the energy captured by photosynthesis is the main reason why microorganisms utilize organic matter, whereby SOM is merely a residual by-product of nutrient storage and a mediator of energy fluxes.