Soil Pore Networks Control Carbon Storage

土壤储存的碳多于地面表面上的所有植被。但是，关于哪些过程有利于在土壤中积累的过程，仍然存在许多未解决的问题。在Helmholtz环境研究中心（UFZ）的领导下，一组土壤科学家开发了一种新方法，以显示碳在土壤中存储在哪里以及在什么条件下。当他们在自然通信中撰写时，主要是土壤孔网络控制碳的空间分布。

在关于气候保护的公开辩论中，土壤的重要性常常被遗忘。但是，土壤比森林或大气层储存的碳多得多。碳的长期存储可能非常复杂。一方面，这取决于大气碳通过根生长，各种混合过程（例如土壤培养或earth的活性）以及溶解有机化合物的渗漏进入土壤。另一方面，这取决于土壤中现有的碳是否可以稳定或被细菌和真菌分解。哪个过程更有效 - 储存或分解 - 主要取决于土壤的结构（例如，有助于运输空气，水和养分的毛孔网络的大小）。UFZ土壤物理学家，研究的主要作者SteffenSchlüter博士说：“如果细菌或真菌菌丝大于储存的土壤中的毛孔，则储存在植物残基和腐殖质中的碳不会分解。”更重要的是：如果毛孔永久充满水，因此没有氧气供应（例如，在完整的泥炭土壤中），细菌发现使用碳更难。Schlüter说：“因此，碳储存在土壤中的决定性因素之一是孔的空间分布。”以前不可能研究毫米和微米大小的孔中有机碳的分布模式。

但是UFZ的科学家现在已经设法做到了。借助他们的新方法，他们可以精确地将碳定位在土壤中。它基于用四氧化osmium的有机化合物染色，该化合物将其粘在含碳的双键上，然后使用X射线计算机断层扫描（CT）进行可视化。通过扫描染色前后的土壤样品，研究人员可以从图像差异中推断碳的分布。到目前为止，只有在精心的同步加速器CT方法的帮助下才有可能。但是，由于在德国只有两个粒子加速器，因此访问受到严重限制。相比之下，X射线CT在德国的土壤科学机构中更为广泛。因此，新方法促进了研究。"You can’t normally look inside the soil. But this methodological innovation allows us to draw conclusions about where and how well carbon is enriched in soil depending on the pore system and organic material such as roots and litter", says Prof. Hans-Jörg Vogel, head of the Department of Soil System Science at the UFZ. This provides important information about processes in the soil and thus also about the consequences they have for the stabilisation and decomposition of carbon in soil.

As an example, the soil scientists tested their methodology at three sites with different soil types and different moisture regimes: a Chernozem site with low annual precipitation at the UFZ research station in Bad Lauchstädt, a fine-textured Luvisol site with seasonal water logging in the foothills of the Alps, and a permanently wet Gleysol site influenced by groundwater near Gießen. The result: in the immediate vicinity of the pores (i.e. in a margin of 50 to 100 micrometres), the concentration of carbon is lower than in the rest of the soil. This is mainly because microbial activity decreases with increasing distance from the pores. "This pattern has been seen at all three sites regardless of the moisture regime. The proximity to the pore system thus favours the decomposition of organic matter, and the distance to these pores promotes the stabilisation of carbon in the topsoil - the layer that is particularly important for agriculture", says Schlüter. In contrast, there are differences in the carbon content around organic material such as plant residues. In dry Chernozem soil, the carbon decreases with distance to the plant residues. The bacteria and fungi are attached to the plant residues so they can easily get at the carbon and metabolise it. The decomposition products then accumulate around the plant residues. In the Gleysol, the opposite was true. The scientists found no enrichment of products around the plant residues. One explanation is that dissolved decomposition products are more easily transported over longer distances under the wet conditions. "The moisture regime strongly influences the stabilisation patterns of carbon in the soil because it controls the extent of carbon relocation from the plant residues into the surrounding soil", says Schlüter.

现在，新的方法论方法开辟了有趣的研究观点，例如碳是如何分布在地下土壤中的（即较深的土壤层最高为一米）。到目前为止，只有间接的证据表明，地下土壤中碳的分布模式与表土中的碳不同。那是因为后者不受耕作的影响，也不是被挖洞的动物的强烈混合。碳只能通过在几个根部积累或溶解有机物质的扩散来达到更深的层。“要了解更多有关这些过程的更多信息。由于气候变化和表层土壤中频繁的干旱，植物越来越缺乏水。” Vogel说，地下土壤对植物生长的重要性正在增加。”新方法，研究人员希望更好地了解更深层的碳存储过程，以及不同形式的土地管理（例如草原使用和可耕种）之间碳平衡差异的原因。

参考：Schlüter S, Leuther F, Albrecht L, et al. Microscale carbon distribution around pores and particulate organic matter varies with soil moisture regime.Nat Commun。2022;13(1):2098. doi:10.1038/S41467-022-29605-W

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