Microscale carbon distribution around pores and particulate organic matter varies with soil moisture regime

Abstract

Soil carbon sequestration arises from the interplay of carbon input and stabilization, which vary in space and time. Assessing the resulting microscale carbon distribution in an intact pore space, however, has so far eluded methodological accessibility. Here, we explore the role of soil moisture regimes in shaping microscale carbon gradients by a novel mapping protocol for particulate organic matter and carbon in the soil matrix based on a combination of Osmium staining, X-ray computed tomography, and machine learning. With three different soil types we show that the moisture regime governs C losses from particulate organic matter and the microscale carbon redistribution and stabilization patterns in the soil matrix. Carbon depletion around pores (aperture > 10 µm) occurs in a much larger soil volume (19–74%) than carbon enrichment around particulate organic matter (1%). Thus, interacting microscale processes shaped by the moisture regime are a decisive factor for overall soil carbon persistence.

Response of subsoil organic matter contents and physical properties to long‐term, high‐rate farmyard manure application

“…The classification of segmented POM into roots, fresh debris and decomposed POM was based on their morphological characteristics. POM is known to change its structural appearance with residence time in soil (Elyeznasni et al, 2012;Juyal et al, 2021;Schlüter et al 2022). Fresh roots are typically coherent, elongated objects; fresh debris has a fragmented structure with large surface area, while decomposed POM becomes more compact and rounded as it ages in soil.…”

“…T A B L E 1 Morphological traits of particulate organic matter objects used for random forest classification into decomposed particulate organic matter, roots and fresh debris (modified from Schlüter et al 2022)…”

“…X‐ray μCT is a powerful tool to characterise the soil structure of undisturbed samples and to analyse the spatial environment of its constituents. New image processing protocols enable the segmentation and classification of POM according to their morphological properties (Elyeznasni et al, 2012; Juyal et al, 2021; Schlüter et al 2022). In this study, we combined soil physical analyses and X‐ray μCT imaging with the chemical characterisation of soil OC to distinguish between different C forms, that is, μCT‐derived estimates of POM fractions classified according to their morphological properties, organic matter embedded in the soil matrix based on μCT‐determined density information and concentrations of soil OC forms, such as total OC (TOC) and water‐extractable OC (WEOC).…”

An open Soil Structure Library based on X-ray CT data

“…This boosted an enormous amount of scientific insight especially with respect to the soil pore structure in relation to water dynamics and solute transport (Wildenschild and Sheppard, 2013;Larsbo et al, 2014;Tracy et al, 2015). More recently, also the importance of soil structure for the turnover of organic matter (Kravchenko et al, 2019;Schlüter et al, 2022b) and as habitat for soil organisms (Juarez et al, 2013;Falconer et al, 2012;Juyal et al, 2019) is studied based on 3D images.…”

Recarbonizing Global Soils for Sustainable Development

“…With ~ 2500 gigatons of carbon, soil is the largest terrestrial sink for organic carbon. Soil organic carbon management is essential for preserving soil health, reducing climate change, and achieving a balance between ecosystem resilience and carbon-atmosphere dynamics (Schmidt et al 2011;Schlüter et al 2022). Soil organic carbon (SOC) offers nutrients to support the growth of soil microflora, fauna, and plants that eventually govern the productivity, biodiversity, and services of any ecosystem (Witzgall et al 2021).…”