Afforestation limits soilborne pathogen dispersal and reorganizes soil microbial risk profiles
The ecological consequences of converting agricultural land into plantation forests remain underexplored, particularly regarding the dynamics of soilborne pathogenic bacteria and their potential risks to human health. In this study, we assessed the composition, transmission pathways, and risk levels of pathogenic bacterial communities across a land-use gradient, from maize farmland to young and mid-aged Chinese pine plantations. Using 156 multi-compartment samples collected in 2019 and 2024, we characterized bacterial communities in soil, roots, leaves, stems, wood, and atmospheric deposition. A combination of high-throughput PacBio sequencing, quantitative PCR, and microbial source-tracking revealed how afforestation affects pathogen distribution and risk potential. Our results showed that afforestation significantly reduced the abundance and diversity of pathogenic bacteria, while increasing the complexity and stability of microbial co-occurrence networks. Pathogen risk was highest in active farmlands and lowest in mid-aged plantations. Source-tracking revealed that non-rhizosphere soil is a dominant source of rhizosphere and endophytic pathogenic bacteria in maize fields, highlighting the rhizosphere as a critical transmission node. In contrast, plantation forests exhibited significantly lower soil-to-plant transmission, reflecting a natural ecological barrier that limits pathogen dispersal and reduces potential health risks. These findings demonstrate that afforestation can mitigate soilborne pathogens' ecological and public health risks by restructuring microbial communities and disrupting pathogen transmission pathways. The study provides critical insight into microbial safety during land-use transitions and highlights the rhizosphere as a key intervention point for managing pathogen spread.