Drivers of soil heterogeneity and their impacts on biogeochemical cycles

Soils are inherently heterogeneous, with spatial variability emerging from interactions among plants, soil microbes and fauna, physicochemical properties, and local climatic and geological conditions. Plants perceive this patchiness and adjust their strategies accordingly; for instance, by increasing investment in arbuscular mycorrhizal fungi (AMF) to access water or nutrients that are scarce or unevenly distributed. These adaptive responses, in turn, influence biogeochemical processes. As agriculture shifts toward practices that reduce environmental impacts, and as extreme climatic events such as drought become more frequent, soil heterogeneity is expected to intensify. This trend highlights the need for crop varieties capable of maintaining performance in increasingly heterogeneous soil environments.

After outlining key drivers of soil heterogeneity, we present two studies demonstrating how plant investment in AMF under water or nutrient limitation shapes belowground carbon dynamics and nutrient acquisition. In the first study, using maize mutants defective in AMF colonization combined with isotopic tracing, we show that AMF enhance plant–microbe interactions by increasing carbon transfer to both AMF and saprotrophic microbes. This higher carbon flow promotes microbial transformation of plant-derived carbon into forms that may contribute to persistent soil organic matter. In the second study, we show that ryegrass compensates for the low solubility of a circular fertilizer by increasing investment in AMF, resulting in phosphorus uptake comparable to that achieved with conventional fertilizer.

Together, these findings illustrate the capacity of crops to buffer resource heterogeneity- whether driven by management or climate change- through symbiotic investment, with cascading consequences for biogeochemical cycling. A key challenge ahead remains to capture soil heterogeneity across scales to better predict its impacts on plant performance and ecosystem processes.