Diversity and Adaptation of Riparian Cottonwoods and Hybrid Poplars - Exploration and Syntheses

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Poplars, Populus trees, provide the foundations for a range of forests around the Northern Hemisphere. They are the most abundant and extensive trees in Canada, and southern Alberta provides a global centre of poplar biodiversity with five species that overlap and the four cottonwoods, or river valley poplars, hybridize. Cottonwoods also provide the parental species for artificial hybrid poplars, the fastest-growing trees in Canada and other temperate regions worldwide. Unfortunately, cottonwood forests have been collapsing, largely due to river damming and water withdrawal for irrigation and other uses, and climate change is amplifying this challenge.*******In this research program, I will extend our investigations into the physiological diversity and adaptations across the North American poplars, and some willows, related shrubs. The riparian forests of southern Alberta provide a unique natural laboratory and studies in British Columbia and the United States will extend the geographic scope. Unlike most plants, poplars are dioecious, either male or female, and we will investigate how the sexes differ, and why. Our studies emphasize physiology, the blending of form and function, and we will compare and contrast the cottonwood species and their hybrids. We will study growth and development, with up-scaling of study components from the isotopic composition of source and xylem water, through measurements of sap flow, photosynthesis and transpiration from leaves and trees, and up to whole ecosystem measurements with eddy covariance flux towers. We will investigate responses to drought and to flooding, and seek to understand how the species are adapted to the diverse environments, such as in river valleys from the mountains to the prairies. We are also considering inheritance and genetics, and manipulating genes for the phytohormone gibberellin, a master regulator of tree form and function. The research will explore the fundamental nature of plant diversity and adaptation, and reveal physiological trade-offs. It could identify traits to benefit poplar plantings across environments and for reclamation. It will contribute towards river regulation to conserve and restore floodplain forests, which provide rich wildlife habitats and benefit water quality. It will also assist in understanding how Canada's deciduous forests may respond to climate change, and considerations of prospective responses such as with plantings for assisted migration.***