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.

夏威夷岛上的多形铁心木（Metrosideros polymorpha）的叶片毛状体（leaf trichomes）含量差异悬殊，沿环境梯度的分布范围为0至约150 g/m²。被毛个体在干旱区域或年轻熔岩流中分布广泛，而无毛个体则在湿润区域或成熟土壤中占优。为阐明被毛个体在干旱环境中的适应策略，我们提出了如下两个研究问题：其一，叶片毛状体是否会提升气体扩散的边界层阻力，进而降低蒸腾速率并提高水分利用效率（water-use efficiency, WUE）；其二，被毛个体是否伴随一系列在干旱环境中具备适应意义的其他叶片与嫩枝性状。我们针对三个干旱程度存在差异的多形铁心木种群开展了详细的生理生态测量。结果发现，在干旱样地中，叶片生物量分配至毛状体的比例最高可达33%。然而，分析结果显示，毛状体对气体交换的影响仅为1%至9%，对水分利用效率的影响可忽略不计，这表明毛状体的功能可能不止于提升水分利用效率。另一方面，被毛个体伴随有更高含量的核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）以及更低的叶面积与边材面积比，这类性状被认为在干旱环境中具有适应性优势。上述结果表明，多形铁心木的被毛个体确实通过一系列性状的改变适应了干旱环境。而叶片毛状体的巨大变异的适应意义仍未明确，其功能可能与提升边界层阻力之外的其他功能相关。