Solar radiation rapidly depolymerizes lignin at wood surfaces exposed outdoors producing a suite of low molecular weight aromatic compounds within weathered wood. Fungi colonizing weathered wood are able to metabolize these aromatic compounds, and many of them also contain high levels of melanin to protect themselves from the harmful effects of UV radiation. Both of these adaptations suggest that solar radiation directly and indirectly influences the colonization of weathered wood by fungi. In this study we test the hypothesis that exposure to solar radiation affects the colonization of wood by fungi and the resulting color of the weathered wood. Lodgepole pine decking samples were exposed outdoors for 40 weeks under filters which blocked selected regions of the solar spectrum while allowing other weathering factors to act on samples. Fungi growing at the surface of wood exposed under the different filters were isolated at the end of the exposure period and identified using molecular techniques. The color of the isolated fungi and the weathered wood were also assessed. Wood exposed under filters that transmitted ultraviolet and/or visible light was more frequently colonized by dark colored fungi such as Aureobasidium pullulans and Hormonema dematioides than samples exposed under filters that blocked these components of the solar spectrum. A. pullulans and H. dematioides were also isolated from wood exposed under filters that blocked UV radiation and visible light, but a greater proportion of lighter fungi such as Epicoccum nigrum and Phoma sp. were found in the weathered wood. The color of weathered wood at the end of the exposure trial partly reflected the pattern of fungal colonization. Wood exposed under filters that blocked UV radiation and visible light was greener and lighter than wood exposed under filters that transmitted these wavelengths. We conclude that solar radiation influences the colonization of wood surfaces by fungi and our findings point to a link between the color of the weathered wood and the fungi that colonize the wood.

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