Digestate from psychrophilic anaerobic digestion reshapes microbial communities and facilitates the recovery of degraded acidic soils under field conditions

Soil degradation constitutes a primary constraint to global ecosystem services, making restoration a critical objective aligned with the United Nations Sustainable Development Goals 13 and 15. While anaerobic digestate is increasingly recognized as a promising amendment for restoring degraded soils within regenerative agriculture and circular bioeconomy frameworks, the mechanistic relationships between digestate quality and soil microbial restructuring remains insufficiently characterized. In this context, the objective of this study was to assess how psychrophilic digestate application influences soil physicochemical properties and microbial community dynamics, and to explore its role in the recovery of degraded soil under field conditions. Results revealed that alleviation of soil chemical stress, primarily associated with acidity, exchangeable Al toxicity, and nutrient imbalance was the primary regulatory factor. The input of exchangeable base cations, coming from digestate, drove a critical increase in pH, mitigating Al toxicity and unlocking P reserves. The observed soil recovery may be associated with the organic matter inputs from the digestate, which can support microbial activity and contribute to improved soil functioning. This was supported by an observed shift in the main soil microbial groups, from Gram-negative to Gram-positive bacteria, which are often associated with higher carbon use efficiency. These findings provided a detailed field-based framework supporting the use of digestate from low-tech digesters working under psychrophilic conditions as a strategic amendment for improving soil chemistry and microbial community composition, while enhancing soil organic C retention. Furthermore, it may offer a viable solution for digestate management aligned with regenerative agriculture and circular bioeconomy goals.