The ecophysiology of leaf cuticular transpiration: are cuticular water permeabilities adapted to ecological conditions?

When the stomata are closed under drought, the only route for water loss from the leaf interior to the atmosphere is across the cuticle. Thus, the extent of cuticular transpiration in relation to the reservoirs of water in the plant and the water acquisition from the soil determines the fitness and survival of the plant. It is, therefore, widely assumed that the cuticular water permeability of plants regularly experiencing drought is comparatively low and, thus, adapted to the environment. To test this hypothesis, 382 measurements of cuticular permeability from 160 species were extracted from the literature published between 1996 and 2017. The data had been produced either by using isolated cuticles and astomatous leaf sides or by measuring the minimum leaf conductance under conditions assumed to induce maximum stomatal closure. The species were assigned to 11 life form groups. Except for two particular cases (epiphytes, and climbers and lianas), the cuticular permeabilities of all groups either did not differ significantly or the available data did not allow a statistical test. In conclusion, present knowledge either does not support the hypothesis that ecological adaptions of cuticular water permeability exist or the available data are insufficient to test it.