Pathways of mineral‐associated soil organic matter formation: Integrating the role of plant carbon source, chemistry, and point of entry
Pathways of mineral‐associated soil organic matter formation: Integrating the role of plant carbon source, chemistry, and point of entry
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DOI：
10.1111/gcb.14482
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发表时间：
2018-11
影响因子：
11.6
通讯作者：
N. Sokol;J. Sanderman;M. Bradford
中科院分区：
文献类型：
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作者：
N. Sokol;J. Sanderman;M. Bradford
为了预测陆地碳循环的行为，了解土壤有机质(SOM)的来源、形成途径和化学成分至关重要。一个新的共识是，慢循环SOM通常由相对低分子量的有机碳底物组成，这些底物以溶解的有机物形式进入矿物土壤，并与矿物表面结合(称为矿物相关OM，或MAOM)。然而，许多争论和相互矛盾的证据仍然存在：(A)MAOM池中的有机C底物是否主要来自地上或地下植物来源，以及(B)C底物在进入MAOM之前是直接吸附在矿物表面还是经历微生物转化。在这里，我们试图调和关于MAOM形成的不同观点，提出一套空间上明确的过程，将植物C源与MAOM形成途径联系起来。具体地说，由于植物C的地下和地上来源进入矿物土壤的空间不同区域，我们认为微生物丰度的细微尺度差异应该决定底物-微生物与底物-矿物相互作用的可能性。因此，在微生物密度较高的地区(如根际和其他微生物热点)，MAOM的形成应该主要通过体内微生物周转途径发生，并有利于C底物的形成，这些底物在纳入MAOM池之前首先被生物合成，具有高的微生物碳利用效率。相反，在微生物密度较低的地区(例如，散装土壤的某些区域)，MAOM的形成应主要通过将完整或部分氧化的植物化合物直接吸附到未定居的矿物表面来实现，从而将碳利用效率的重要性降至最低，并有利于具有强烈“吸附亲和力”的C基质。因此，通过这个框架，我们描述了生物和非生物控制在毛姆动态中的首要地位如何不是相互排斥的，而是如何在空间上决定的。这样的理解可能对于更准确地模拟不同空间尺度上的土壤有机质动态是不可或缺的。
To predict the behavior of the terrestrial carbon cycle, it is critical to understand the source, formation pathway, and chemical composition of soil organic matter (SOM). There is emerging consensus that slow‐cycling SOM generally consists of relatively low molecular weight organic carbon substrates that enter the mineral soil as dissolved organic matter and associate with mineral surfaces (referred to as “mineral‐associated OM,” or MAOM). However, much debate and contradictory evidence persist around: (a) whether the organic C substrates within the MAOM pool primarily originate from aboveground vs. belowground plant sources and (b) whether C substrates directly sorb to mineral surfaces or undergo microbial transformation prior to their incorporation into MAOM. Here, we attempt to reconcile disparate views on the formation of MAOM by proposing a spatially explicit set of processes that link plant C source with MAOM formation pathway. Specifically, because belowground vs. aboveground sources of plant C enter spatially distinct regions of the mineral soil, we propose that fine‐scale differences in microbial abundance should determine the probability of substrate–microbe vs. substrate–mineral interaction. Thus, formation of MAOM in areas of high microbial density (e.g., the rhizosphere and other microbial hotspots) should primarily occur through an in vivo microbial turnover pathway and favor C substrates that are first biosynthesized with high microbial carbon‐use efficiency prior to incorporation in the MAOM pool. In contrast, in areas of low microbial density (e.g., certain regions of the bulk soil), MAOM formation should primarily occur through the direct sorption of intact or partially oxidized plant compounds to uncolonized mineral surfaces, minimizing the importance of carbon‐use efficiency, and favoring C substrates with strong “sorptive affinity.” Through this framework, we thus describe how the primacy of biotic vs. abiotic controls on MAOM dynamics is not mutually exclusive, but rather spatially dictated. Such an understanding may be integral to more accurately modeling soil organic matter dynamics across different spatial scales.