ADAPTIVE RELATIONSHIP BETWEEN LEAF WATER REPELLENCY,STOMATAL DISTRIBUTION,AND GAS EXCHANGE

Although numerous studies have considered the functional significance of the terrestrial plant leaf surface, the importance of water repulsion for enhancing photosynthetic carbon uptake (CO₂) has not been recognized and appears to involve an array of structural adaptations. The large majority of species tested had leaf surfaces that repelled water to such an extent that varying degrees of water-bead formation occurred. On more wettable leaves, the formation of a water surface film (dewfall) severely curtailed photosynthetic CO, uptake in the field, most likely because CO₂ diffuses 10⁴ times slower in water than air. Water bead formation not only enabled maintenance of high photosynthetic rates but also increased water use efficiency several fold. In 3 of 5 species tested in the field, water bead formation after artificial wetting resulted in greater stomatal opening and increases in photosynthesis of up to 34%. The most nonwettable leaf surface on a given leaf also had all or the majority of the leaf's stomata in 50 of the 57 species tested, indicating a potentially strong adaptive relationship between leaf surface wettability, stomatal occurrence, and photosynthetic performance.