Linkage between trichome morphology and leaf optical properties in New Zealand alpine Pachycladon (Brassicaceae)

Trichomes are important regulators of leaf radiation absorptance and thus modulate the carbon, water and energy balance of pubescent plants. This study assessed leaf hair characteristics and leaf optical properties of four species of alpine Pachycladon (Brassicaceae). Two of the pubescent Pachycladon species exhibited different trichome morphological characteristics but only small variations in leaf hair density. These structural differences explained much of the variation in optical properties between species. Pachycladon stellatum exhibited the highest proportion of dendritic trichomes (87%), with forked and simple trichomes more common in the other species. This high proportion of dendritic trichomes contributed to the c. 8.3% reflectance in physiologically important regions of the electromagnetic spectrum in P. stellatum leaves compared with c. 6.5% reflectance in P. enysii leaves, which showed similar leaf hair density but fewer dendritic trichomes (7%). Together, these data indicate an under-appreciated role for trichome morphology in regulating leaf absorption of radiation in Pachycladon.