The positive effect of soil organic matter (SOM) on crop yield has historically been attributed to the ability of SOM to supply crops with nitrogen and water. Whether management-induced increases in SOM meaningfully supplement water supply has received recent scrutiny, introducing uncertainty to the mechanisms by which SOM benefits crops. Here, we posit that to benefit crops SOM does not need to increase the supply of a growth-limiting resource; it only needs to facilitate root access to extant resource stocks. We highlight evidence for the ability of SOM to alleviate negative impacts of inadequate aeration (mainly waterlogging) and compaction on roots. Waterlogging, even if transient, can permanently downregulate root biosynthesis and call for expensive growth of new roots. Management practices that promote SOM reduce waterlogging by accelerating water infiltration and may promote aeration in non-saturated soils. Compaction as a restriction to root development manifests in drying soils, when mechanical impedance (MI) inflates photosynthate required to extend root tips, leading to short, thick, and shallow roots. SOM reduces MI in dry soils and is associated with root channels to subsoil, granting crops access to deep soil water. Both waterlogging and compaction necessitate additional belowground investment per unit resource uptake. In this framework, crop response to SOM depends on interactions of crop susceptibility to inadequate aeration or compaction, soil moisture, and “baseline” soil aeration and compaction status. By exploring the proposition that SOM catalyzes resource uptake by permitting root development, future research may constrain crop yield improvements expected from SOM management.

中文翻译：

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土壤有机质作为作物资源捕获的催化剂

土壤有机质 (SOM) 对作物产量的积极影响历来归因于 SOM 为作物提供氮和水的能力。管理引起的 SOM 增加是否有意义地补充水供应最近受到了审查，这给 SOM 使作物受益的机制带来了不确定性。在这里，我们假设为了使作物受益，SOM 不需要增加限制生长的资源的供应；它只需要促进对现有资源库的根访问。我们强调了 SOM 能够减轻通气不足（主要是涝渍）和压实对根部的负面影响的能力的证据。内涝，即使是短暂的，也会永久性地下调根的生物合成，并需要昂贵的新根生长。促进 SOM 的管理做法通过加速水渗透来减少涝渍，并可能促进非饱和土壤的通气。当机械阻抗 (MI) 使扩展根尖所需的光合作用膨胀时，压实作为对根发育的限制表现在干燥土壤中，导致根短、粗和浅。SOM 可减少干燥土壤中的 MI，并与通往底土的根系通道相关，使作物能够获得深层土壤水。内涝和压实都需要对每单位资源吸收进行额外的地下投资。在这个框架中，作物对 SOM 的反应取决于作物对通气或压实不足的敏感性、土壤湿度以及“基准”土壤通气和压实状态之间的相互作用。通过探索 SOM 通过允许根系发育来催化资源吸收的命题，