Vascular constraints on leaf out and flowering in plants

开花和发芽等重大事件的时间调节了植物对环境的反应，并对种群增长、与其他生物的相互作用和大规模生态系统过程具有影响。对于温带树木在春天落叶等重大事件发生的时间是否存在生理和解剖学上的限制，人们知之甚少。没有这些知识，理解不同的时间策略对生态和进化的影响以及预测物种如何应对环境变化是具有挑战性的。该项目的主要目标是研究树木水运系统的季节变化与早春资源重新分配的时间之间的关系。本研究将强调资源动员在支持叶片和花朵生产中的重要性，并探讨维管解剖学和生理学是否可以解释春季物候的种间变化。大部分工作将由本科生、研究生和一名博士后完成，他们将有机会学习有价值的技能，并与多个地点的科学家建立联系。研究成果将用于开发植物生理学的实验室课程，直接将树木的维管生物学与抗冻性联系起来。该课程将在明尼苏达大学德卢斯分校为高中生举办的年度课程中使用。新组织的生长依赖于在维管系统中运输的资源，因此，降低维管功能的环境条件，包括低温，会限制新组织的发育。温带环境中的大多数物种必须在早春时重新激活或修复它们的维管系统，才能支持嫩叶和花朵。一般来说，植物恢复维管功能有两种策略：激活先前分化的细胞和/或从形成层初始产生新的运输细胞。据推测，依赖于产生新的运输细胞（至少在木质部）的植物不能支持早期的叶片脱落。如果木质部和韧皮部都是如此，那么物种用来恢复维管功能的机制就可以决定植物在生长季节多早产生叶子和花朵。为了验证这一假设，本研究将描述植物物候与落叶木本植物维管再激活机制之间的关系。由于花水化并不总是需要两个维管系统，本研究还将探讨花水化的机制，并考虑其对花抗冻性的影响。该研究将增加对春季维管再激活的认识，这是季节性气候下植物生理的核心部分，并有助于理解维管系统中一个关键但尚未得到充分研究的过程。

The timing of major events like flowering and germination mediates how plants respond to their environment, and has implications for population growth, interactions with other organisms, and large scale ecosystem processes. Relatively little is known about whether there are physiological and anatomical constraints on the timing of major events like leaf out in the spring in temperate trees. Without this knowledge, it is challenging to understand the ecological and evolutionary implications of different strategies in timing and to predict how species will respond to environmental change. The primary goal of this project is to examine the relationship between seasonal changes in the water transport system of trees and the timing of the re-distribution of resources in the early spring. This research will highlight the importance of resource mobilization in supporting leaf and flower production and examine whether vascular anatomy and physiology could explain interspecific variation in spring phenology.  A major part of the work will be completed by undergraduates, graduate students and a postdoctoral researcher, who will have the opportunity to learn valuable skills and network with scientists at multiple sites.  Research results will be used to develop laboratory curriculum on plant physiology that directly connects the vascular biology of trees to freezing tolerance. The curriculum will be used during an annual program for high school students held at the University of Minnesota Duluth. New growth relies on resources transported in the vascular system, and therefore environmental conditions that reduce vascular function, including cold temperatures, can limit the development of new tissue. Most species in temperate environments must re-activate or repair their vascular system in the early spring before they can support young leaves and flowers. In general, there are two strategies plants use to restore vascular function: activating previously differentiated cells and/or producing new transport cells from cambial initials. It has been hypothesized that plants that rely on the production of new transport cells (at least in the xylem) cannot support early leaf out. If this is true for both the xylem and phloem, then the mechanism that species use to restore vascular function could determine how early in the growing season plants can produce leaves and flowers. To test this hypothesis, this study will characterize the relationship between plant phenology and the mechanism of vascular re-activation in deciduous, woody species. Because floral hydration does not always require both parts of the vascular system, this research will also examine the mechanism of floral hydration and consider its implications for floral freezing tolerance. This research will increase knowledge of vascular re-activation in the spring, which is a core part of plant physiology in seasonal climates, and help to understand vascular re-activation, a critical but understudied process in the vascular system.