Digestate-based fertilization supports lettuce growth with limited impacts on phyllosphere bacterial communities

Digestate-based fertilizers are increasingly used in agriculture as part of circular nutrient management strategies, yet their effects on phyllosphere bacterial communities and antimicrobial resistance remain insufficiently understood. In this study, lettuce (Lactuca sativa L.) was grown under greenhouse conditions and subjected to different digestate-based fertilization strategies to evaluate their effects on plant performance, leaf nutrient content, cultivable fecal indicator bacteria and Salmonella, antibiotic resistance genes (ARGs), and phyllosphere bacterial communities. Microbiological quality was assessed through the analysis of coliforms and Escherichia coli by the most probable number (MPN) method and the detection of Salmonella spp. using standard culture-based procedures. ARG abundance was quantified by quantitative real-time PCR, while bacterial community composition was characterized using 16S rRNA gene sequencing and multivariate analyses. Notably, split application of digestate produced plant growth and leaf nutrient levels comparable to those achieved with inorganic fertilization, without increasing the abundance of the evaluated ARGs or the occurrence of fecal indicator bacteria and Salmonella, despite their detection in the initial digestate material. Fertilization strategy influenced phyllosphere bacterial community composition, whereas total bacterial abundance remained stable across treatments. Overall, these findings provide novel insights into digestate-based fertilization strategies by showing that, under the experimental conditions, digestate application supported lettuce productivity with limited impacts on phyllosphere bacterial communities.