Is Leaf Water-Repellency and Cuticle Roughness Linked to Flooding Regimes in Plants of Coastal Wetlands?

Abstract

Owing to periodic inundation, wetland plants may have adapted to minimize leaf gas exchange impairments. Increasing the leaf cuticle surface roughness might contribute to buffer flooding stress, since it might increase both leaf water repellency (i.e. leaf hydrophobicity) and the presence of gas films. Thus, a higher leaf hydrophobicity, as well as an increased cuticle roughness, can be expected in species subject to continuous water-logging. We tested this hypothesis by: 1) measuring the contact angle in the liquid-solid interface on leaves of 52 plant species from three coastal wetlands with different diversity and flooding regime in Baja California, Mexico, and 2) by performing scanning electron microscopic analyses in the most hydrophilic and hydrophobic species. Contrary to our expectations, the highest values of leaf water repellency were found in species from non-flooded areas adjacent to the wetlands, whereas neutral leaf water repellency values were found in species subject to flooding, as indicated by the contact angle measurements (77 to 100°). The most water repellent species presented a striking layer of wax on top of the leaf cuticles, while the lest water repellent species were mostly glabrous, which suggest that the augmentation of wax covering in the cuticle might be responding to other environmental factors, such as irradiation.