Microbial biomass – not diversity – drives soil carbon and nitrogen mineralisation
Soil microbial communities drive essential ecosystem functioning, driving biogeochemical cycles and contributing to climate regulation. Yet, their complexity makes it difficult to quantify how microbial properties – especially biomass and diversity – shape carbon (C) and nitrogen (N) cycling. Most models predicting soil organic matter dynamics at the ecosystem scale still overlook microorganisms entirely.
A new study developed by HoliSoils researchers directly addresses this knowledge gap by testing whether incorporating microbial biomass and diversity (based on taxonomic identification) improves predictions of soil heterotrophic respiration and net nitrogen mineralisation across diverse Spanish soils.
The results are clear: microbial biomass enhanced model performance and almost linearly controlled carbon mineralisation, whereas microbial diversity had only minor and negative effects on the carbon and nitrogen mineralisation rates. In the conditions of our study, microbial diversity added complexity in the model without substantial gains in prediction.
By showing that microbial biomass, not diversity, drives soil carbon and nitrogen mineralisation in this modeling framework, the study offers a compelling argument for integrating microbial activity into models while cautioning against added complexity that does not yield better predictions.
This article was written by Elisa Bruni (Institut Pierre-Simon Laplace).
More information:
Bruni, Elisa, et al. 2025. Microbial biomass–not diversity–drives soil carbon and nitrogen mineralization in Spanish holm oak ecosystems.” Geoderma, 460 (2025): 117408. https://doi.org/10.1016/j.geoderma.2025.117408
