Architecture of soil microaggregates: Advanced methodologies to explore properties and functions

Abstract

The functions of soils are intimately linked to their three‐dimensional pore space and the associated biogeochemical interfaces, mirrored in the complex structure that developed during pedogenesis. Under stress overload, soil disintegrates into smaller compound structures, conventionally named aggregates. Microaggregates (<250 µm) are recognized as the most stable soil structural units. They are built of mineral, organic, and biotic materials, provide habitats for a vast diversity of microorganisms, and are closely involved in the cycling of matter and energy. However, exploring the architecture of soil microaggregates and their linkage to soil functions remains a challenging but demanding scientific endeavor. With the advent of complementary spectromicroscopic and tomographic techniques, we can now assess and visualize the size, composition, and porosity of microaggregates and the spatial arrangement of their interior building units. Their combinations with advanced experimental pedology, multi‐isotope labeling experiments, and computational approaches pave the way to investigate microaggregate turnover and stability, explore their role in element cycling, and unravel the intricate linkage between structure and function. However, spectromicroscopic techniques operate at different scales and resolutions, and have specific requirements for sample preparation and microaggregate isolation; hence, special attention must be paid to both the separation of microaggregates in a reproducible manner and the synopsis of the geography of information that originates from the diverse complementary instrumental techniques. The latter calls for further development of strategies for synlocation and synscaling beyond the present state of correlative analysis. Here, we present examples of recent scientific progress and review both options and challenges of the joint application of cutting‐edge techniques to achieve a sophisticated picture of the properties and functions of soil microaggregates.

Structure–function co‐evolution during pedogenesis—Microaggregate development and turnover in soils

“…Joint explorative studies and experiments were realized within the 6-year coordinated research program. From all studies, microaggregates were separated and analyzed for composition, structure, and properties of intact microaggregates by combining state-of-the-art instrumental techniques in a joint fashion (Amelung et al, 2024(Amelung et al, , this issue). 2018(Amelung et al, , 2020Schweizer et al, 2021).…”

Grassland management intensity determines root development, soil structure, and their interrelationship: Results of a regional study of Leptosols in the Swabian Alps

“…In contrast to conventional root washing methods, µCT provides nondestructive 3D imaging that preserves plant integrity and allows repeated measurements, for example, to study juvenile root development in pots (Blaser et al, 2020). µCT also has advantages compared to the determination of soil physical parameters using soil cylinders, particularly with regard to the visibility of whether the sample is really undisturbed (Amelung et al, 2023). Disadvantages of µCT compared to conventional methods can include limited sample size due to the complexity and cost of the measurement and limited sample volume due to the size limitation, which is device-specific, and there is also a tradeoff between resolution and sample volume (Zhang et al, 2023).…”