Data from: Influence of leaf trichomes on boundary layer conductance and gas-exchange characteristics in Metrosideros polymorpha (Myrtaceae)

The amount of leaf trichomes of Metrosideros polymorpha varies enormously-ranging from 0 to ca 150 g/m2 across environmental gradients
on the island of Hawaii. Pubescent individuals are abundant in dry areas or on young lava flows whereas glabrous individuals are abundant in wet areas or on developed soils. To understand the adaptive strategies of pubescent individuals in arid environments, we addressed the following questions: (1) whether leaf trichomes increase the boundary layer resistance to gas diffusion, which in turn reduces the transpiration rate and increases water-use efficiency (WUE); and (2) whether pubescent individuals are accompanied by a suite of other leaf and shoot traits that have adaptive significances in arid environments. We made detailed ecophysiological measurements on Metrosideros polymorpha in three populations that varied in the level of aridity. We found the large allocation of leaf mass to trichomes up to 33% at the arid site. However, our analyses showed that trichomes had small effects (1-9%) on gas exchanges and negligible effects on WUE, suggesting the trichome may have roles beyond increasing WUE. On the other hand, pubescent individuals were accompanied by a higher amount of Rubisco and a lower leaf- to sapwood area ratio, which are considered adaptive in arid environments. These results suggest that pubescent individuals of M. polymorpha are indeed adaptive to arid environments with changes in a suite of traits. The adaptive significance of the enormous variation of trichome remains unclear and may be related to functions other than increasing boundary layer resistance.