Temporal dynamics of airborne fungi in Swedish forest nurseries

In Sweden, reforestation of managed forests relies predominantly on planting nursery-produced tree seedlings. However, the intense production using containerized cultivation systems (e.g., high seedling density, irrigation from above, regular fertilization) creates favorable conditions for fungal infections. Despite the harmful role of diseases in forest nurseries, the origin and dispersal factors of fungal pathogens remain largely unknown. A better understanding of the airborne spread of pathogens could improve the prediction of fungal infection, ultimately optimizing preventative methods and decreasing the use of fungicides. This study investigated the temporal dynamics of airborne fungi in forest nurseries, with a focus on fungal pathogens. Airborne fungi were monitored in four Swedish forest nurseries over two growing seasons using spore traps and high-throughput sequencing. Fungal pathogens were identified using bioinformatics and quantified with quantitative PCR. Results showed strong temporal shifts of airborne fungal diversity and community composition following the growing seasons. The airborne spread included high abundances of important fungal pathogens (e.g., Cladosporium sp., Botrytis cinerea, Alternaria sp., Sydowia polyspora, and Melampsora populnea) with individual temporal and spatial variations. In general, the deposited spore loads of nursery pathogens correlated positively with increased temperature and negatively with higher precipitation. This was expressed the strongest for Cladosporium sp., Alternaria sp., and M. populnea, which suggests a higher availability of fungal inoculum in warm and dry periods. This study highlights the influence of seasonality on the temporal dynamics of economically important fungal pathogens in Swedish forest nurseries, which should be considered in the development of a local decision support system.IMPORTANCEFungal diseases in forest nurseries have significant environmental and economic impacts on the tree seedling production. This study highlights the role of seasonality in the airborne spread of fungal pathogens in Swedish forest nurseries. By analyzing airborne fungal spores using advanced sequencing and monitoring techniques, key fungal pathogens and their dispersal patterns over two growing seasons were identified. The findings indicate that warmer, drier periods may increase the spread of fungal pathogens, emphasizing the need for targeted preventative measures. Understanding these temporal dynamics can help optimize the use of fungicides in forest nurseries, thereby promoting more sustainable and environmentally friendly management practices. This research provides valuable insights for improving disease management in forest nurseries, ultimately supporting sustainable tree seedling production.