Rhizosphere as driver of subsoil organic matter distribution and composition

在FOR1806研究单元的第一阶段，我们证明了根沉积对地下土壤有机碳的数量和组成的巨大影响。从格林德瓦尔德中心研究点和各区域研究点可以看出，不仅根际土壤有机质含量明显大于无根块状土壤，而且其化学成分也存在差异。对于格林德沃，我们发现根际土壤和散装土壤在颗粒和粘土相关SOM方面存在明显的化学差异。根际土壤C/N比较低，根系附近有机质分解较少，贡献较大（表现为较高的O/N-烷基C）。这些初步结果表明，根沉积在特定根际结构（宏观和微观聚集）的建立中起着重要作用，这可能促进地下土壤中有机碳的储存。然而，目前尚不清楚根沉积在多大程度上影响矿物依赖的聚集，从而影响地下有机碳组成和储存。本建议的目的是了解生长根和死根对底土，特别是底土根际土壤有机碳的组成、分布和数量的影响。土壤有机碳分布的空间分异将主要体现在根系生长进入无根底土的过程中。我们将致力于实施新的方法来研究活根和死根周围的地带性梯度，因为这些区域在土壤聚集和有机质稳定中起着重要作用。与有机丰富的表层土相比，这些影响导致底土的空间异质性增加。为了研究这些影响和机制，关键是使用受控的环境条件，这只能在实验室条件下实现，基于研究单位第一阶段获得的现场土壤数据。我们将使用一系列越来越复杂的实验，从人工根系到山毛榉幼苗的自然根系。然后将这些数据与研究单位实地调查的结果进行交叉核对。

During the first phase of the research unit FOR1806 we demonstrated the large effect of rhizodeposition on the amount and composition of soil organic carbon in subsoils. As shown for the central research site Grinderwald and the regional sites, not only the amount of soil organic matter is considerably larger in the rhizosphere in comparison to the root free bulk soil, but also the chemical composition is different. For Grinderwald we found clear chemical differences between rhizosphere and bulk soil for both particulate as well as clay associated SOM. The rhizosphere soil showed lower C/N ratios and a higher contribution of less decomposed OM (indicated by higher O/N-alkyl C proportions) in the vicinity of roots. These first results point to an important role of rhizodeposition for the build-up of specific rhizosphere structures (macro and micro-aggregation) that may foster organic carbon storage in subsoils. However, it remains unclear to which extent rhizodeposition affects mineralogy-dependent aggregation and thereby influences subsoil organic carbon composition and storage. The objectives of the present proposal are to understand the influence of growing and dead roots on the composition, distribution and the amount of soil organic carbon in the subsoil and specifically in the subsoil rhizosphere. The main aspect will be the evolving spatial differentiation of the soil organic carbon distribution due to roots growing into previously root free subsoil. We will work on the implementation of new methods to study zonal gradients around living and dead roots, as these zones play an important role in soil aggregation and thus also OM stabilization. These effects lead to increased spatial heterogeneities in subsoils in contrast to organic rich topsoils. To study these effects and mechanisms it is crucial to use controlled environmental conditions as can only be achieved under laboratory conditions, based on the field soil data obtained in the first phase of the research unit. We will use a cascade of experiments with increasing complexity starting from artificial root systems to natural roots of beech seedlings. These are then cross-checked with the results from the investigations at the field sites of the research unit.