COLLABORATIVE RESEARCH: How do seedlings survive? Hydraulics, carbon acquisition and drought tolerance in the earliest phases of tree growth

通过减少更新和随后的成虫死亡率，树种的分布可以随着时间的推移而缩小，或者可以通过苗木的建立而扩大到超出目前的分布边界。因此，我们预测未来物种分布的能力的一个关键组成部分是了解苗木建立的机制，这需要苗木生理学的基本知识。从根到叶的水分途径对于维持叶片的水分状况和允许气孔保持开放至关重要，从而通过光合作用捕获碳。然而，植物中的水分运输很容易受到干燥引起的变化的影响，包括血管组织栓塞(即气泡形成)。这项研究的总体目标是了解防止树苗水力失灵(即灾难性的栓塞症)的机制，从而确保树苗存活和建立时有足够的光合作用。将对正在生长的幼苗的存活、生长、生理和解剖进行测量，以评估干燥耐受性和干燥对光合作用的影响，并确定调节幼苗水分损失的结构何时形成。这项研究的结果可以直接用于植被对气候变化反应的建模预测，因为苗木存活可能是物种分布的主要决定因素。这些发现也将引起政策制定者和土地管理者的兴趣，他们对干旱对某些物种的生产力和分布的潜在影响感兴趣。它们也将引起树木和木本作物育种者的兴趣，这些育种者关心的是识别与特定环境下的生存和足够生产力相关的特征。此外，测量幼苗水力参数的想法和方法将引起植物科学界的兴趣，并可能为新的研究活动领域提供一个跳板。该项目包括培养两名研究生、几名本科生和高中生。

Tree species distributions can shrink over time through reduced regeneration and subsequent adult mortality or they can expand via seedling establishment beyond current distribution boundaries. Therefore, a critical component of our ability to predict future species distributions is an understanding of the mechanisms of seedling establishment, which requires a fundamental knowledge of seedling physiology. The water pathway from the root to the leaf is critically important for maintaining leaf water status and allowing stomata to stay open, resulting in carbon capture through photosynthesis. However, water transport in the plant is vulnerable to desiccation-induced changes, including vascular tissue embolism (i.e. air bubble formation). The overall objective of this research is to understand the mechanisms responsible for prevention of hydraulic failure (i.e. catastrophic embolism) in tree seedlings, thereby ensuring adequate photosynthesis for their survival and establishment. Survival, growth, physiology and anatomy of growing seedlings will be measured to assess desiccation tolerance and the impacts of drying on photosynthesis, and to determine when structures that regulate seedling water loss develop. Results from this research can be directly used in modeled predictions of vegetation responses to climate change because seedling survival is likely a primary determinant of species distributions. These findings will also be of interest to policy makers and land managers who are interested in potential drought impacts on productivity and distributions of certain species. They will also be of interest to tree and woody crop breeders concerned with identifying traits associated with survival and adequate productivity in given environments. In addition, the ideas and methodology of measuring young seedling hydraulic parameters will be of interest to the plant science community and could provide a springboard for a new area of research activity. The project includes training of two graduate students, several undergraduate students and high school students.