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Most studies exploring the relation between the quality of organic substrates and microbial activity have been carried out with individual substrates. However, they have largely overlooked potential effects that might occur when microorganisms simultaneously process a heterogeneous mixture of organic substances. We investigated whether the degree of molecular richness of substrate mixtures had an impact on the overall activity of microbial communities, measured as heat dissipation over a day, in a laboratory incubation experiment. Topsoil samples were taken from a Swedish long-term field trial, established in 1983, in which a crop rotation dominated by spring cereals was either under-sown with perennial ryegrass as a cover crop or was without cover crops. No significant differences in the cumulative heat dissipation between soil with or without cover crops were observed. When all substrate mixtures were evaluated, the substrate richness was not significantly correlated with the overall microbial activity. However, we observed a bell-shaped curve between the total microbial activity and the nominal oxidation state of carbon (C) in the substrate mixtures. In most cases, the measured heat dissipated from soils that received substrate mixtures was significantly higher than the theoretically expected heat dissipation. The latter was based on the weighted sum of heat dissipated of individual substrates. This pattern was more visible in soil without cover crops than in soil with cover crops. The higher-than-expected heat dissipation from substrate mixtures suggests that the response of soil microbial communities to diverse substrates is not simply additive. There are several possible explanations for the observations made: (i) interactions among microbial metabolic pathways, (ii) added substrates may be preferentially used, and (iii) concentration of all the substrates in the mixtures was lower than when added individually, and therefore the metabolic pathways for each substrate was less likely to be saturated. Chemodiversity, the diversity of organic chemical compounds, is often not considered in models evaluating the dynamics of soil organic matter. Our results warrant further investigations into microbial metabolism and the processing of heterogeneous organic substances in order to constrain microbial- and substrate-specific models of soil organic matter.

Nyckelord

Environment; microbiology and biology; organic chemistry; soil biochemistry

Publicerad i

Soil Science and Plant Nutrition
2026
Utgivare: TAYLOR AND FRANCIS LTD

SLU författare

UKÄ forskningsämne

Markvetenskap

Publikationens identifierare

  • DOI: https://doi.org/10.1080/00380768.2026.2616657

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/146005