Vascular constraints on leaf out and flowering in plants

开花和萌发等重大事件的时间安排影响植物对环境的反应，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产生影响。对于温带树木春季落叶等重大事件的发生时间是否存在生理和解剖学上的限制，人们知之甚少。如果没有这种知识，就很难理解不同策略在时机上的生态和进化影响，并预测物种将如何应对环境变化。该项目的主要目标是研究树木水分运输系统的季节变化与早春资源重新分配时机之间的关系。这项研究将强调资源调动在支持叶片和花生产中的重要性，并检查维管解剖和生理是否可以解释春季物候的种间差异。这项工作的主要部分将由本科生、研究生和一名博士后研究员完成，他们将有机会学习宝贵的技能，并与多个地点的科学家建立网络。研究成果将用于开发植物生理学实验室课程，将树木的维管生物学与耐寒性直接联系起来。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。新的生长依赖于血管系统中运输的资源，因此降低血管功能的环境条件，包括寒冷的温度，可能会限制新组织的发育。在温带环境中的大多数物种必须在初春重新激活或修复它们的维管系统，才能支持幼叶和花朵。一般说来，植物有两种策略来恢复维管功能：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，依赖产生新的运输细胞(至少在木质部中)的植物不能支持早期脱叶。如果木质部和韧皮部都是这样，那么物种用来恢复维管功能的机制可能决定植物在生长季节的早期产生叶子和花的时间。为了验证这一假设，这项研究将表征植物物候与落叶木本植物维管重新激活机制之间的关系。由于花的水合作用并不总是需要维管系统的两个部分，本研究还将研究花的水合作用的机制，并考虑其对花的耐寒性的影响。这项研究将增加对春季维管重新激活的了解，这是季节性气候下植物生理学的核心部分，并有助于理解维管重新激活这一关键但尚未被研究的过程。

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.