Stabilization of organic matter by soil minerals - Investigations of density and particle-size fractions from two acid forest soils

authored by

Klaus Kaiser, Karin Eusterhues, Cornelia Rumpel, Georg Guggenberger, Ingrid Kögel-Knabner

Abstract

We tested the hypothesis whether organic matter in subsoils is a large contributor to organic carbon (OC) in terrestrial ecosystems and if survival of organic matter in subsoils is the result of an association with the soil mineral matrix. We approached this by analyzing two forest soil profiles, a Haplic Podzol and a Dystric Cambisol, for the depth distribution of OC, its distribution among density and particle-size fractions, and the extractability of OC after destruction of the mineral phase by treatment with hydrofluoric acid (HF). The results were related to indicators of the soil mineralogy and the specific surface area. Finally, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX) was used to visualize the location of OC at mineral surfaces and associations with elements of mineral phases. The subsoils (B and C horizons) contained 40-50% of the soil OC including the organic forest floor layers. With increasing depth of soil profiles (1) the radiocarbon ages increased, and (2) increasing portions of OC were either HF-soluble, or located in the density fraction d > 1.6 g cm ^-3, or in the clay fraction. The proportions of OC in the density fraction d > 1.6 g cm^-3 were closely correlated to the contents of oxalate and dithionite-citrate-bicarbonate-extractable Fe (r² = 0.93 and 0.88, P <0.001). SEM-EDX analyses suggested associations of OC with aluminum whereas silicon-enriched regions were poor in OC. The specific surface area and the microporosity of the soil mineral matrix after destruction of organic matter were less closely correlated to OC than the extractable iron fractions. This is possibly due to variable surface loadings, depending on different OC inputs with depth. Our results imply that subsoils are important for the storage of OC in terrestrial ecosystems because of intimate association of organic matter with secondary hydrous aluminum and iron phases leading to stabilization against biological degradation.

External Organisation(s)

University of Bayreuth
Technical University of Munich (TUM)

Type

Article

Journal

Journal of Plant Nutrition and Soil Science

Volume

165

Pages

451-459

No. of pages

9

ISSN

1436-8730

Publication date

02.08.2002

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Soil Science, Plant Science

Sustainable Development Goals

SDG 15 - Life on Land

Electronic version(s)

https://doi.org/10.1002/1522-2624(200208)165:4<451::AID-JPLN451>3.0.CO;2-B (Access: Closed)