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Field-to-forest fungal spillover is a biotic edge effect of coffee in Costa Rica


Abstract

Agricultural expansion creates mosaic landscapes where managed land borders natural ecosystems, facilitating the movement of organisms between habitats. Ecological spillover from natural systems to crops has been previously examined, but the extent to which populations amplified by agriculture move into adjacent forests remains largely unexplored. We investigated whether Costa Rican coffee fields act as reservoirs for foliar fungi that, because of high crop density and phylogenetic signal in plant-fungal associations, may particularly affect close relatives of coffee (Rubiaceae) in the forest understory. Field surveys, airborne propagule sampling, and metabarcoding along transects at the coffee-forest border revealed declining leaf spot incidence with distance into the forest for Rubiaceae but not non-Rubiaceae hosts, in parallel with declines in the dominant fungal order on coffee leaves, Pleosporales, and 19 coffee-associated taxa. Ninety-three coffee-associated taxa, including many potential plant pathogens, showed higher modeled abundance on forest Rubiaceae than forest non-Rubiaceae hosts. Our findings suggest that crops can act as reservoirs for fungi colonizing adjacent forest plants, disproportionately affecting hosts more closely related to the crop. These plants may face increased disease pressure, leading to changes in forest understory composition near the crop-forest border. Phylogenetically structured spillover represents an underappreciated edge effect in fragmented landscapes.

Acknowledgements

We are indebted to the farmers who allowed us access to their coffee farms and forests, without whom none of this work would have been possible. The staff at the Las Cruces Biological Station and the Organization for Tropical Studies (OTS) deserve much gratitude for creating a comfortable and productive place to work. Enrique Castro Fonseca at OTS, and staff at the National Commission for the Management of Biodiversity (CONAGEBIO) in Costa Rica and USDA PPQ in Beltsville, Maryland, USA assisted with securing permits for research and collecting. The authors extend their gratitude to Mauricio Barquero Céspedes and Diego Mesa Solis for building the passive air samplers. We also thank Michael Atencio Picado and Erick Barrantes Fallas, who helped deploy and maintain the air samplers, Fiona Wolfe Travers for her assistance in the field, and Ethan Strom for his assistance in the lab. This work was supported by the resources and staff at the University of Minnesota Genomics Center (https://genomics.umn.edu). The bioinformatic pipelines of this study were executed using the Center for Computationally Assisted Science and Technology (CCAST) at North Dakota State University, made possible in part by NSF MRI Award No. 2019077.

Funding

This material is based upon work supported by the U.S. National Science Foundation DEB Awards 2048131 and 2037121 to LAW and 2120085 awarded to BB, as well as the Graduate Research Fellowship awarded to JAL (Grant No. 2137101). GE was supported by Donald & Beverly Stone Fellowships (Fund 507/557) through the Organization for Tropical Studies.

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Jeffrey A. Lackmann.

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Lackmann, J.A., Bachelot, B., Lindell, C. et al. Field-to-forest fungal spillover is a biotic edge effect of coffee in Costa Rica.
Nat Commun (2026). https://doi.org/10.1038/s41467-026-75178-3

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