Process sequence of soil aggregate formation disentangled through multi-isotope labelling

verfasst von

Wulf Amelung, Nele Meyer, Andrey Rodionov, Claudia Knief, Michaela Aehnelt, Sara L. Bauke, Danh Biesgen, Stefan Dultz, Georg Guggenberger, Maguy Jaber, Erwin Klumpp, Ingrid Kögel-Knabner, Volker Nischwitz, Steffen A. Schweizer, Bei Wu, Kai U. Totsche, Eva Lehndorff

Abstract

Microaggregates (<250 µm) are key structural subunits of soils. However, their formation processes, rates, and transformation with time are poorly understood. We took advantage of multiple isotope labelling of potential organic gluing agents and inorganic building units to unravel their role in soil aggregation processes being initiated with and without plant growth. We added ¹³C-labelled extracellular polymeric substances (EPS), ¹⁵N-labelled bacteria, ⁵⁷Fe-labelled goethite, and ²⁹Si-labelled montmorillonite to fine soil <250 µm of an Ap horizon from a Stagnic Luvisol, which was planted with Festuca heteromalla or kept bare in a climate chamber. Samples were taken after 4, 12, and 30 weeks, and separated into free (f) and occluded (o) microaggregates of different sizes (<20 µm, 53–20 µm, 250–53 µm), and in stable macroaggregates (>250 µm) that resisted 60 J mL⁻¹ ultrasonic dispersion. Afterwards, we assessed the C, N, Fe, and Si stable isotope composition in each size fraction. After four weeks we found a rapid build-up of stable macroaggregates comprising almost 50 % of soil mass in the treatment with plants and respective soil rooting, but only 5 % when plants were absent. The formation of these stable macroaggregates proceeded with time. Soil organic carbon (SOC) contents were elevated by 15 % in the large macroaggregates induced by plant growth. However, the recovery of EPS-derived ¹³C was below 20 % after 4 weeks, indicating rapid turnover in treatments both with and without plants. The remaining EPS-derived C was mainly found in macroaggregates when plants were present and in the occluded small microaggregates (<20 µm) when plants were absent. The excess of bacterial ¹⁵N closely followed the pattern of EPS-derived ¹³C (R² = 0.72). In contrast to the organic gluing agents, the goethite-⁵⁷Fe and montmorillonite-²⁹Si were relatively equally distributed across all size fractions. Overall, microaggregates were formed within weeks. Roots enforced this process by stabilizing microaggregates within stable macroaggregates. As time proceeded the labelled organic components decomposed, while the labelled secondary oxides and clay minerals increasingly contributed to aggregate stabilization and turnover at the scale of months and beyond. Consequently, the well-known hierarchical organization of aggregation follows a clear chronological sequence of stabilization and turnover processes.

Organisationseinheit(en)

Institut für Bodenkunde
AG Bodenchemie

Externe Organisation(en)

Rheinische Friedrich-Wilhelms-Universität Bonn
Forschungszentrum Jülich
Universität Bayreuth
Friedrich-Schiller-Universität Jena
Sorbonne Université
Technische Universität München (TUM)

Typ

Artikel

Journal

GEODERMA

Band

429

ISSN

0016-7061

Publikationsdatum

01.01.2023

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Bodenkunde

Ziele für nachhaltige Entwicklung

SDG 13 – Klimaschutzmaßnahmen

Elektronische Version(en)

https://doi.org/10.1016/j.geoderma.2022.116226 (Zugang: Offen)