This study investigates interactions between soil organic carbon (SOC) and calcium (Ca). It reveals that Ca contributes to SOC stability even in acidic soils, a finding that departs from previous assumptions that Ca's role is limited to neutral or alkaline soils. It also investigates the formation mechanisms driving the association of Ca with a characteristic fraction of SOC, highlighting the importance of decomposition processes in its formation. In this work, the authors employ advanced spectromicroscopy and targeted experiments to confirm that Ca binds SOC compounds rich in aromatic and phenolic groups after decomposition, preventing their loss as dissolved organic carbon. The identification of this biogeochemical mechanism has direct implications for improving soil carbon models and guiding Ca amendment practices in agriculture, enhancing soil carbon retention and contributing to climate resilience.

This is an important forum article highlighting the lack of awareness into plant physiology in global soil carbon research. This issue is highly relevant as much of soil carbon cycling is driven by plant activity, in particular in the rhizosphere or related to plant symbionts. Their results are clear—the large majority of soil carbon studies do not include plant physiology even though a plant physiological perspective could provide novel or more mechanistic insights on soil carbon processes and could inform a new direction in soil carbon modelling.

This article demonstrates that soil mineralogy, not just clay content, determines the radiocaesium interception potential of soils, i.e. the absorption of 137Cs and hence its bioavailability. It, therefore, highlights the need for recalibration of existing 137Cs bioavailability models to predict regional contamination risk, but also the need for more careful soil analysis at the regional scale.