Temperature distribution in bryophyte canopies and its relationship to water flux

Growth of mosses is largely dictated by patterns of water loss due to their unusual ectohydric water transport and storage system. Thus, it is crucial to understand the mechanisms governing water loss. We seek to elucidate the factors that control water loss from moss shoot surfaces using a novel analytical technique: 3D thermal imaging. This enables the simultaneous examination of canopy structure and temperature distribution. While studies have previously investigated how variation in canopy structure affects water loss in windy conditions, such inquiry has not been applied to still conditions where temperature gradients should matter. We examined temperature distributions within canopies of two common forest floor species during drying (Pleurozium schreberi and Rhytidiadelphus triquetrus); we quantified canopy structure, temperature gradients, water flux, and their relationships to give further insight into the magnitude of temperatures within canopies and their potential importance. R. triquetrus had a significantly rougher canopy with a lower bulk density than P. schreberi. Both species showed a significant increase in canopy mean temperature during drying, but no significant difference between species. We obtained a temperature gradient of about 3-5°C within the canopies of our samples during the course of natural drying, with low temperatures achieved through evaporative cooling. R. triquetrus exhibited a significantly larger temperature gradient than did P. schreberi, and calculated air density gradients differed significantly with respect to drying and species. These results indicate that structural differences contribute to thermal gradients and may cause differences in water fluxes, which could result from micro-scale convection currents within the canopy.