Synergistic Effects of Light and Water on Physiological Diversification in the Hawaiian Llobeliads

夏威夷小叶莲是开花植物中适应性辐射最壮观的例子之一，从完全开放到密集遮荫的微型场所，年降雨量为500至12,000毫米。先前的研究提供了该分支的分子系统发育，记录了11个代表性物种沿光子通量密度梯度（PFD）的分布，并通过田间和普通花园研究证明了静态和动态光合光响应及其相关叶片性状对PFD的适应。栖息地的多样化通常伴随着光合生理的变化，这种变化遵循了适应阳光与阴影的经典模式。然而，光的可利用性几乎不可避免地与降雨和蒸发需求的变化相关，而后者受到空气温度、相对湿度和阳光与阴凉微生境热负荷差异的影响。因此，目前尚不清楚——在夏威夷小叶植物中，或在所有陆地植物中——光合反应和相关叶片性状沿PFD梯度的变化在多大程度上反映了对光本身变化的适应，或相对于需求的水分供应，或两者兼而有之。初步数据表明，光和水分的有效性相互作用，形成了不同生境的小叶属植物的光合光响应和相关的叶片性状。该研究验证了水和光有效性的相互作用对几种夏威夷小叶虫适应一系列光和水分梯度的生理多样化和适应性进化路径的重要影响。实验将描述田间条件下的水分关系，包括叶片水势、气孔对湿度的响应、光合作用对VPD的响应、叶片水力导度和水力脆弱性的研究。在一个普通的花园实验将被用来分析生态和进化的变化在水的关系，水力学，光合作用，相关的叶片性状，和整个植物生长在普通条件下。最后，研究将确定在夏威夷群岛广泛的环境梯度中，生理特征是否发生了进化趋势。研究结果将为陆地植物气体交换策略的演变提供基础见解。通过在明确的系统发育背景下对密切相关的分类群进行此类研究，将得出关于各种特征的进化途径以及生态与祖先在塑造当今物种特征中的作用的重要推论。外联活动包括为欧空局的生态学教学问题和实验开发一个模块；与火山艺术与科学学院和Kamehameha学校Kea 'au校区合作，为K-8学生开发一个关于当地植物适应的模块；并通过与UH-Hilo REU项目和ESA SEEDS项目的协调，为来自代表性不足群体的本科生提供暑期研究机会。

The Hawaiian lobeliads (Campanulaceae) are one of the most spectacular examples of adaptive radiation in flowering plants, ranging from fully open to densely shaded microsites and from 500 to 12,000 mm annual rainfall. Prior research has provided a molecular phylogeny for this clade, documented the distribution of 11 representative species along a gradient of photon flux density (PFD), and demonstrated the adaptation to PFD of static and dynamic photosynthetic light responses and associated leaf traits via field and common-garden studies. Diversification in habitat has generally been accompanied by shifts in photosynthetic physiology that follow classic patterns of adaptation to sun vs. shade. However, light availability is almost inevitably correlated with variation in rainfall and evaporative demand, with the latter affected by differences in air temperature, relative humidity, and heat load in sunny vs. shady microsites. It is thus unclear - in Hawaiian lobeliads, or across land plants - the extent to which variation in photosynthetic responses and associated leaf traits along PFD gradients reflects adaptation to variation in light per se, moisture supply relative to demand, or both. Preliminary data suggest that light and moisture availability interact to shape photosynthetic light responses and associated leaf traits in lobeliads native to different habitats. The research tests the hypothesis that the interaction of water with light availability critically influenced the path of physiological diversification and adaptive evolution in several Hawaiian lobeliads adapted to a range of light and moisture gradients. Experiments will characterize water relations under field conditions, including studies of leaf water potential, stomatal response to humidity, photosynthetic response to VPD, leaf hydraulic conductance and hydraulic vulnerability. Experiments in a common garden will be used to analyze ecological and evolutionary shifts in water relations, hydraulics, photosynthesis, associated leaf traits, and whole plant growth under common conditions. Finally, research will determine if evolutionary trends occur in physiological traits across broad environmental gradients in the Hawaiian Islands. Findings will provide fundamental insights into the evolution of gas exchange strategies in land plants. By conducting such studies on closely related taxa in the context of an explicit phylogeny, important inferences will be drawn about evolutionary pathways for various traits, and the role of ecology vs. ancestry in shaping the characteristics of present-day species. Outreach activities include developing a module for the ESA's Teaching Issues and Experiments in Ecology; coordinating with the Volcano School of Arts and Sciences, and Kamehameha Schools Kea`au campus to develop a module on local plant adaptation for K-8 students; and providing summer research opportunities for undergraduate students from underrepresented groups through coordination with the UH-Hilo REU program & ESA SEEDS program.