Can enzyme activities assist soil health assessment in the EU Soil Monitoring and Resilience Directive?

The EU Soil Monitoring and Resilience Directive (SMRD) establishes a harmonized framework for assessing soil health across Member States, focusing on chemical, physical, and biological descriptors. Currently, basal respiration is the only biological indicator of soil functionality suggested at the EU level, highlighting the need for complementary indicators that capture ecosystem processes and resilience under climate change and land management pressures.

Microbial-based functional indicators represent a promising solution, as soil microorganisms rapidly respond to environmental stress and drive key biogeochemical processes. Drawing on a series of case studies, literature reviews, and findings from EU-funded projects carried out by our research group (LIFE and Next Generation EU), we emphasize the critical role of soil eco-enzymes as indicators of soil health conditions. Enzyme activities, such as β-glucosidase (BG), acid phosphatase (AP), and N-acetyl-β-D-glucosaminidase (NAG), could be suitable descriptors of functional microbial biodiversity. In view of this, soil enzyme activities could be introduced as new descriptors in the Annex I during the Directive’s scheduled revision in 2033.

Microbial-released enzyme balance, under specific environmental conditions and spatial scales, could also contribute to evaluating and predicting the rate and efficiency of organic matter decomposition and immobilization, thus regulating the balance between stored C pools and CO₂ emissions. Integrating enzyme tests into SMRD monitoring protocols would provide robust descriptors of microbial processes influencing organic matter turnover. This approach strengthens the Directive’s capacity to evaluate soil health and resilience, offering a sensitive, easy-to-implement, and cost-effective functional indicators aligned with EU sustainability goals for 2050.