Fungal pigmentation responses to microclimatic variables in isolated forest patches in Northern Sweden

Abstract: Investigating functional traits is an important tool for understanding fungal communities, yet ecological functions of fungal pigmentation remain poorly investigated. Recent studies support the thermal-melanism hypothesis for fungal color lightness in relation to macroclimate, but it remains unclear if microclimate also affects fungal pigmentation. In this study I use fruit bodies of wood-living polypores to further investigate this subject. While previous studies have used database-derived color lightness from photos often taken under unknown and non-standardized conditions, here I extract all color values from standardized photos taken in situ. In contrast to previous studies that have only examined fungal color lightness, I also studied the other components of the CIE L'a'b' color space, which may be related to e.g. protection, thermoregulation or signaling. I investigated community-level fungal pigmentation of pore surfaces and caps of polypores in fragmented forest patches in northern Sweden, in relation to microclimate proxies, deadwood availability and surrounding landscape structure. Two types of multiple linear regression models were used, one for community weighted means (CWM) and one for the coefficient of variance (CV) of patch level pigmentation. While no support was found for the thermal-melanism hypothesis in this study, saturation in the yellow spectrum was positively related to canopy cover and forest patch size. Variance in lightness of pore surfaces and in saturation in the red spectrum of caps was also positively related to diversity of decay stages and forest patch size respectively. These results indicate previously unknown relationships between fungal pigmentation and environment which warrant further research.