A thinner jacket for frosty and windy climates? Global patterns in leaf cuticle thickness and its environmental associations.

Plant cuticles protect the interior tissues from ambient hazards, including desiccation, UV light, physical wear, herbivores and pathogens. Consequently, cuticle properties are shaped by evolutionary selection. We compiled a global dataset of leaf cuticle thickness (CT) and accompanying leaf traits for 1212 species, mostly angiosperms, from 293 sites representing all vegetated continents. We developed and tested 11 hypotheses concerning ecological drivers of interspecific variation in CT. CT showed clear patterning according to latitude, biome, taxonomic family, site climate and other leaf traits. Species with thick leaves and/or high leaf mass per area tended to have thicker cuticles, as did evergreen relative to deciduous woody species, and species from sites that during the growing season were warmer, had fewer frost days and lower wind speeds, and occurred at lower latitudes. CT-environment relationships were notably stronger among nonwoody than woody species. Heavy investment in cuticle may be disadvantaged at sites with high winds and frequent frosts for 'economic' or biomechanical reasons, or because of reduced herbivore pressure. Alternatively, cuticles may become more heavily abraded under such conditions. Robust quantification of CT-trait-environment relationships provides new insights into the multiple roles of cuticles, with additional potential use in paleo-ecological reconstruction.