Carbon dynamics in soils – Does the diversity of organic inputs matter? : a bioenergetics approach

Abstract

The diversification of agroecosystems is an attractive agricultural practice that can lead to climate change mitigation/adaptation by stimulating carbon sequestration. As the chemical composition of plants can vary, the diversification of plant communities can impact the chemical properties of the organic inputs to soil. The changes in the chemical properties of organic inputs to soil, such as their molecular diversity, may influence both microbial activity and the composition of soil organic matter. Therefore, the overall aim of this thesis was to investigate how diversified organic inputs affect the soil microbial processing. Specifically, how do diversified organic inputs to soils affect below-ground organic matter properties and how does this affect soil microbial activity? Topsoil samples from various soil systems from cereal dominated agriculture to woodland, including a long-term field trial with Salix, were used in the different studies. The chemical composition of soil organic matter was characterised, and the energy content of hot water-extractable organic matter and its nominal oxidation state were determined. Microbial activity was analysed by measuring heat dissipation from soil by isothermal calorimetry, and microbial energetic return on investment was calculated. The activity of soil microbial communities is related to the properties of the available soil organic matter, most notably the potential return on energetic investment that the microbial communities can obtain when consuming the organic substrates. The diversity of the available substrates did not seem to affect microbial activity, but their average energetic properties did. Microbial activity reached a maximum when microorganisms processed substrate mixtures with redox properties that matched their preferences. Only at low levels of molecular diversity, microbial community happened to process substrate mixtures in a non-additive, synergistic manner. The longer-term fate of the C inputs may also be affected by the characteristics of the organic inputs: the composition and diversity of soil organic matter was influenced by Salix species, but not by varieties, when not confounded by the heterogeneity in soil properties. Soil C dynamics can only be fully understood through the prism of interactions between organic substances and microorganisms and may not be modulated by managing the diversity of organic inputs but rather by influencing their intrinsic energetic properties.

Keywords

diversification; community composition; soil; organic matter; microbial activity; return on investment; bomb & isothermal calorimetry; spectroscopy; mass spectrometry; mångfald; samhällets sammansättning; jord; organiskt material; mikrobiell aktivitet; energetiskt ’return on investment’; kalorimtetri; spektroskopi; masspektrometri

Published in

Acta Universitatis Agriculturae Sueciae
2025, number: 2025:36
Publisher: Swedish University of Agricultural Sciences

SLU Authors

• Dufour, Louis

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Soil Science

Publication identifier

• DOI: https://doi.org/10.54612/a.6nite9eqlc
• ISBN: 978-91-8046-471-0
• eISBN: 978-91-8046-521-2

Permanent link to this page (URI)

https://res.slu.se/id/publ/132976