Melanic pigments and canopy-specific elemental concentration shape growth rates of the lichen Lobaria pulmonaria in unmanaged mixed forest

Abstract How do elemental composition (published data) and melanin (new data) shape the relative growth rate (RGR; new data) of the cephalolichen Lobaria pulmonaria, a member of the Lobarion community? We transplanted L.pulmonaria onto Picea glauca x engelmannii branches in three unmanaged canopy settings in inland British Columbia: within Populus dripzones supporting Lobarion; outside dripzones supporting Lobarion; and outside dripzones without Lobarion (non-Lobarion). A year later, lichen RGR was highest in the Lobarion, intermediate in the dripzone, and lowest in the non-Lobarion). RGR increased with Ca- and P-concentration, but declined with Zn, S, initial level of melaninic pigmentation, tree height, and elevation. Bark pH lost significance in multiple regression models when lichen elemental concentrations were included. Along canopy openness gradients, acclimation by the solar radiation-induced melanin had compensated for varying light. By the end of the experiment, melanin thus did not affect RGR probably because it normalized the light in the photobiont layer across sites.