Adaptive physiology of riparian cottonwoods and hybrid poplars

棉杨是一种杨树，适应整个北半球的河岸(泛滥平原)地带。种间杂交自然发生在物种重叠的区域，也可以人工培育出杂交杨树，这是加拿大生长最快的树木。由于河流筑坝和改道的影响以及其他人类影响，北美西部的棉杨种群已经崩溃。我建议进一步研究河岸棉杨的生态生理学及其保护。调查将涉及三个重叠的领域，水力学、激素和杂交。水力学研究将调查连接溪流、河岸基质、根、芽和大气的水通量。树木水分关系的方面将调查水力传导性和木质部空化的脆弱性，木质部导管中的空气栓塞破坏了传导水分的能力。这些研究将比较和对比四个加拿大杨树物种，研究雄性和雌性之间的差异，还将调查来自艾伯塔省西南部复杂杂交区的自然发生的杨树杂交种，以及人工交叉杂交种。这些研究将调查负责适应不同环境的生理过程，我们已经确定了一些“幸存者”，这些树在长期压力后仍然存在，可能对干旱有独特的适应能力。植物激素研究将探讨激素赤霉素(GA)在协调棉杨生长对环境条件变化的反应中的作用，研究还将调查转基因修改GA水平和作用的后果。这些研究将(1)揭示杨树和杨树的生态生理适应；(2)通过河流治理和水分管理，促进本地杨树的恢复；(3)鉴定可遗传的生理性状，使其能够发展适应干旱的杂交杨树。

Cottonwoods are Populus species that are adapted to riparian (floodplain) zones throughout the Northern Hemisphere. Interspecific hybrids occur naturally in zones where species overlap and are also artificially produced to create hybrid poplars, the fastest-growing trees in Canada. Due to the impacts of river damming and diversion and other human influences, cottonwood populations have collapsed across western North America. I propose to further investigate the ecophysiology of riparian cottonwoods and their conservation. Investigations will involve three overlapping areas, hydraulics, hormones and hybridization. Studies of hydraulics will investigate water fluxes linking streams, riparian substrates, roots, shoots and the atmosphere. Aspects of tree water relations will investigate hydraulic conductance and vulnerabilities to xylem cavitation, air embolism in the xylem vessels that destroys the capacity to conduct water. The studies will compare and contrast the four Canadian cottonwood species, study differences between males and females, and will also investigate naturally occurring Populus hybrids from the complex hybrid zone in southwestern Alberta, and artificial intersectional hybrids. The studies will investigate the physiological processes responsible for adaptation to differing environments and we have identified some 'survivors', trees that have persisted after chronic stress and may be uniquely drought-adapted. Plant hormones studies will investigate the roles of the hormone gibberellin (GA) in the coordination of cottonwood growth responses to changing environmental conditions and studies will also investigate consequences of transgenic modification of GA level and action. These investigations will (1) reveal ecophysiological adaptations of cottonwoods and poplars, (2) contribute to the restoration of native cottonwoods through river regulation and water management, and (3) identify heritable physiological traits that may enable the development of drought-adapted hybrid poplars.