TY - JOUR

T1 - Disentangling the effects of OM quality and soil texture on microbially mediated structure formation in artificial model soils

AU - Bucka, Franziska B.

AU - Felde, Vincent J.M.N.L.

AU - Peth, Stephan

AU - Kögel-Knabner, Ingrid

N1 - Funding Information: This research was funded by the Deutsche Forschungsgemeinschaft (DFG) within the research unit “MAD Soil - Microaggregates: Formation and turnover of the structural building blocks of soils” (FOR 2179). The authors gratefully acknowledge Shu-Yin Tung, Gabriele Albert, Petra Bucher and Christine Pfab from the Technical University of Munich for their help during the lab work; Vera Baumert for establishing the PLFA extraction method in our group at the Technical University of Munich; Pedro Paulo de C. Teixeira for practical assistance with the PLFA extractions and helpful discussions about the gained data; Svenja Roosch and Daniel Uteau from the University of Kassel for their help with the dry crushing; and Angelika Kölbl from the University Halle-Wittenberg for contributing ideas and knowledge regarding the experimental design. The authors thank two anonymous reviewers for evaluating the manuscript and providing very thoughtful comments and constructive feedback, which helped us to improve the manuscript.

PY - 2021/12/1

Y1 - 2021/12/1

N2 - The interaction between mineral particles and soil organic matter (SOM) is an important and complex process during soil structure formation, in which the effects of soil texture and OM properties are intertwined. Within the SOM, there are residues of particulate organic matter (POM) of various sizes, as well as microbial necromass co-existing. These OM residues undergo microbial decay whose products stabilize particle connections and thus induce aggregate formation. We developed an experimental set-up to study early soil structure formation within a controlled lab environment. Artificial soil microcosms with a mineral mixture of different textures (clay loam, loam, and sandy loam) were used to perform a short-term incubation for 30 days under constant water tension. OM was added individually either as POM of two different size classes (milled hay litter, 0.63–2 mm and <63 µm, respectively) or bacterial necromass (Bacillus subtilis). The dry mixing process and incubation of the mineral mixtures led to particle–particle interactions and fine particle coatings of the sand grains as shown by a reduction in the specific surface area (N 2-BET). The OM residues were quickly accessed and degraded by microbes (peak in CO 2-release within the first 10 days of incubation), which induced the formation of water-stable aggregates. The POM of both sizes induced predominantly the formation of macroaggregates (0.63–30 mm) with a mass contribution of 72% to 91%, irrespective of the mixtures’ texture. The bacterial necromass induced a texture-dependent formation of macro- and microaggregates (63–200 µm), with larger aggregates in sand-rich mixtures. The different aggregate sizes were related to differences in the developed microbial community, as obtained by PLFA analysis. The bacterial necromass induced a microbial community dominated by bacteria, whereas the POM fostered a high relative abundance of fungi, whose hyphae could enmesh and stabilize large aggregates in all textures. The formed aggregates are water-stable but have a very low mechanical stability. Dry crushing with a mechanical loading frame revealed that very low forces (<4 N) were sufficient for breaking the aggregates down. Microbial growth and degradation of the OM residues led to OM patches occupying <17% of the mineral surfaces after the incubation, suggesting that the aggregates are loosely connected structures, bound together by some distinct spots of processed OM acting as gluing joints. This initially formed scaffold holds particles in place for further stabilization processes and resists immersion in water but exhibits no stability toward mechanical forces.

AB - The interaction between mineral particles and soil organic matter (SOM) is an important and complex process during soil structure formation, in which the effects of soil texture and OM properties are intertwined. Within the SOM, there are residues of particulate organic matter (POM) of various sizes, as well as microbial necromass co-existing. These OM residues undergo microbial decay whose products stabilize particle connections and thus induce aggregate formation. We developed an experimental set-up to study early soil structure formation within a controlled lab environment. Artificial soil microcosms with a mineral mixture of different textures (clay loam, loam, and sandy loam) were used to perform a short-term incubation for 30 days under constant water tension. OM was added individually either as POM of two different size classes (milled hay litter, 0.63–2 mm and <63 µm, respectively) or bacterial necromass (Bacillus subtilis). The dry mixing process and incubation of the mineral mixtures led to particle–particle interactions and fine particle coatings of the sand grains as shown by a reduction in the specific surface area (N 2-BET). The OM residues were quickly accessed and degraded by microbes (peak in CO 2-release within the first 10 days of incubation), which induced the formation of water-stable aggregates. The POM of both sizes induced predominantly the formation of macroaggregates (0.63–30 mm) with a mass contribution of 72% to 91%, irrespective of the mixtures’ texture. The bacterial necromass induced a texture-dependent formation of macro- and microaggregates (63–200 µm), with larger aggregates in sand-rich mixtures. The different aggregate sizes were related to differences in the developed microbial community, as obtained by PLFA analysis. The bacterial necromass induced a microbial community dominated by bacteria, whereas the POM fostered a high relative abundance of fungi, whose hyphae could enmesh and stabilize large aggregates in all textures. The formed aggregates are water-stable but have a very low mechanical stability. Dry crushing with a mechanical loading frame revealed that very low forces (<4 N) were sufficient for breaking the aggregates down. Microbial growth and degradation of the OM residues led to OM patches occupying <17% of the mineral surfaces after the incubation, suggesting that the aggregates are loosely connected structures, bound together by some distinct spots of processed OM acting as gluing joints. This initially formed scaffold holds particles in place for further stabilization processes and resists immersion in water but exhibits no stability toward mechanical forces.

KW - Aggregate formation

KW - Dry crushing

KW - Incubation experiment

KW - PLFA analysis

KW - Specific surface area

KW - Water tension

UR - http://www.scopus.com/inward/record.url?scp=85106327828&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2021.115213

DO - 10.1016/j.geoderma.2021.115213

M3 - Article

VL - 403

JO - GEODERMA

JF - GEODERMA

SN - 0016-7061

M1 - 115213

ER -