The role of clay content and mineral surface area for soil organic carbon storage in an arable toposequence

Steffen A Schweizer,Carmen Höschen,Ingrid Kögel-Knabner,Carsten W Mueller,Pavel Ivanov

doi:10.1007/s10533-021-00850-3

Steffen A Schweizer, Carmen Höschen + Show 3 more

Open Access

https://doi.org/10.1007/s10533-021-00850-3

Copy DOI

Abstract

Correlations between organic carbon (OC) and fine mineral particles corroborate the important role of the abundance of soil minerals with reactive surfaces to bind and increase the persistence of organic matter (OM). The storage of OM broadly consists of particulate and mineral-associated forms. Correlative studies on the impact of fine mineral soil particles on OM storage mostly combined data from differing sites potentially confounded by other environmental factors. Here, we analyzed OM storage in a soil clay content gradient of 5–37% with similar farm management and mineral composition. Throughout the clay gradient, soils contained 14 mg OC g−1 on average in the bulk soil without showing any systematic increase. Density fractionation revealed that a greater proportion of OC was stored as occluded particulate OM in the high clay soils (18–37% clay). In low clay soils (5–18% clay), the fine mineral-associated fractions had up to two times higher OC contents than high clay soils. Specific surface area measurements revealed that more mineral-associated OM was related to higher OC loading. This suggests that there is a potentially thicker accrual of more OM at the same mineral surface area within fine fractions of the low clay soils. With increasing clay content, OM storage forms contained more particulate OC and mineral-associated OC with a lower surface loading. This implies that fine mineral-associated OC storage in the studied agricultural soils was driven by thicker accrual of OM and decoupled from clay content limitations.

Highlights

There is considerable debate about the factors and mechanisms responsible for organic matter (OM) storage in soils
Across the wide gradient of 5–37% clay content, we found a bulk organic carbon (OC) content of 14.2 ± 0.4 mg OC g-1 on average with a range of 9–23 mg OC g-1 not systematically related to clay contents (Fig. 1a)
Combined density and size fractionation enabled us identify clay-related changes for two major forms of OM storage, such as the particulate OM occluded in aggregates and OM associated with mineral surfaces

Summary

Introduction

There is considerable debate about the factors and mechanisms responsible for OM storage in soils. Interactions between soil organic carbon (OC) and mineral soil particles reduce the accessibility of OC for degraders, governing its susceptibility to mineralization and release into the atmosphere (Torn et al 1997; Schmidt et al 2011; Kleber et al 2015, 2021). Fine mineral soil particles and aggregated soil structures exert control over OC content through sorption of organic matter (OM) at mineral surfaces and occlusion in aggregates, protecting particulate OM and its decomposition products from further degradation (Jones and Edwards 1998; Baldock and Skjemstad 2000; Schmidt et al 2011; Cotrufo et al 2015). Direct evidence relating OM storage to mineral surface area is often lacking

Objectives

Methods

Results

Discussion

Conclusion