Soil is one of the most complex and dynamic ecosystems on Earth, a living network of minerals, microbes, roots, and moisture, all interacting across micrometer scales. Deep within these hidden layers, microbial communities orchestrate processes that sustain life above ground: nutrient cycling, carbon turnover, and even the degradation of pollutants. Yet, understanding what truly happens inside these environments has always been a challenge.
In their recent publication, “Comparison of Isothermal Microcalorimetry Versus Respirometry Assays to Evaluate Short- and Long-term Impact of Microplastics on Soil Microbial Activity” (Macan et al., 2025), researchers from the Institute for Sustainable Agriculture (IAS-CSIC, Spain) took an innovative step toward unveiling that hidden world.
Using the calScreener™ microcalorimetry platform from Symcel they were able to continuously measure the metabolic heat generated by soil microbes, effectively tracking microbial life in real time, without disturbing the system. This simple yet profound shift in how we measure biological activity opens an entirely new way of looking at soil health.
Traditionally, soil respiration assays and enzymatic tests have provided valuable insights, but they tend to capture just one dimension of microbial life — how much oxygen is consumed, or how much CO₂ is released. Microcalorimetry, in contrast, measures the total energetic fingerprint of the system. Every reaction that releases energy, from the oxidation of organic matter to the slow metabolism of dormant microbes, contributes to the thermogram.
In this study, the calScreener made it possible to distinguish between active and autoclaved soils, to capture metabolic shifts under glucose addition, and to reveal subtle but meaningful differences between soils exposed to biodegradable and conventional microplastics. The results show not only that soil microbial activity changes with the presence of these materials, but also that microcalorimetry can detect these shifts much earlier and more sensitively than traditional methods. But perhaps the most fascinating aspect is what this tells us about the nature of soil systems themselves.
Each soil particle is its own universe, a patchwork of microhabitats where oxygen levels, nutrient concentrations, and moisture can vary dramatically across micrometers. Within those layers, microbial sub-communities adapt, compete, and collaborate in ways we are only beginning to understand. Two soils that appear identical on the surface may have completely different metabolic signatures depending on their texture, organic matter, and microbial composition.
This is where microcalorimetry shows its real strength. By capturing the combined heat flow of all microbial processes, it allows us to observe not just one metabolic pathway but the integrated energy landscape of a complex community. It’s a holistic view — a system-level signal from the entire microbiome.
If we can measure how different soils respond metabolically to pollutants like microplastics, we might start identifying specific microbial fingerprints, or bioenergetic signatures, of contamination. We could begin to design or select microbial consortia optimized for bioremediation, capable of breaking down plastics or restoring degraded soils. Or we could develop biosensor soils, where changes in thermal activity reveal early signs of pollution long before visible effects occur.
This study demonstrates how we can use microcalorimetry as a bridge between microbiology and sustainability science. By letting the soil speak in heat, we gain a new lens for seeing how life adapts, survives, and potentially heals our planet.