How should we model soil processes?
Soils are fundamental components of any terrestrial ecosystem. Organic matter from plant residues is transformed into mineral compounds that both contribute to greenhouse gas accumulation in the atmosphere (like carbon dioxide) and support plant growth (inorganic nitrogen and phosphorus). Therefore, organic matter transformations in soils are key for both climate mitigation and vegetation productivity. But how can we predict these important functions when land management changes or under future climatic conditions?
To predict soil processes and their consequences on ecosystems we use mathematical models—basically a set of formulas that calculate how soil carbon, nitrogen, and water vary through time depending on environmental conditions and land management. Modelling soils is not easy, as organic matter transformations depend on many processes mediated by soil microorganisms and fauna that are still in part poorly understood, making it hard to translate them into mathematical formulas. A major challenge is to represent in our models how microorganisms and soil fauna live and transform organic matter.
In HoliSoils we are advancing these models by including microbial processes and soil fauna (see Holisoils’ deliverables from WP2), but we are not alone—soil and ecosystem modellers worldwide are joining forces to tackle this issue. A special issue of the journal Soil Biology and Biochemistry brought together the most recent advances in soil modelling, and an editorial piece led by HoliSoils partner Stefano Manzoni summarized the findings of those studies.
Novel models are describing microbial processes driving soil functions, such as carbon and nutrient acquisition from organic matter; allocation of the acquired resources to growth of new biomass, to enzymes fuelling resource acquisition, or to mineralized products (e.g., carbon dioxide, inorganic nutrients); and microbial responses to changing environmental conditions (e.g., soil moisture, temperature). There is also a growing recognition that microorganisms are not static—their communities change due to ecological and evolutionary pressures selecting the most fit taxa. Eco-evolutionary models are exploring how these adaptations alter the way microorganisms transform and help store organic matter in soils.
Despite these advances, major challenges remain. As models become more realistic by better representing microorganisms, they can also become less robust because complex models are harder to use and can give unexpected results. To overcome this challenge, we must develop models that predict measurable soil properties, so that we can test model outputs against observations. It is also important to balance the representation of microorganism biology and ecology, and that of the soil physical environment. We can have detailed microbial models, but without a realistic description of the soil habitat and conditions, such models would not yield reliable predictions. HoliSoils is helping in this effort by providing guidelines for soil measurements and monitoring (see Holisoils’ deliverables from WP1 and WP3), as well as state-of-the art datasets to test our new models.
This article was written by Stefano Manzoni (Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University).
