Diversity and Adaptive Physiology of Riparian Cottonwoods and Hybrid Poplars

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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 as five species 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. Unfortunately, riparian cottonwood forests have been collapsing, largely due to river damming and water withdrawal for irrigation and other human uses. In this research program, I will investigate the physiological diversity and adaptations across the North American cottonwoods. The riparian forests of southern Alberta provide a rich and unique 'natural laboratory' and I will extend studies into British Columbia and Saskatchewan. We are also studying narrowleaf cottonwoods from their full latitudinal range from Alberta to Arizona. Unlike most plants, poplar trees are either male or female and we will investigate how the sexes differ, and why. Our studies investigate 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, and analyze photosynthesis, carbon capture, and transpirational water use. 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 will also investigate variation in specific genes and through whole genome sequencing, seeking associations between genetic markers and physiological traits. These important and novel investigations will contribute to the knowledge required to conserve and restore our floodplain forests, which provide rich wildlife habitats, stabilize stream banks, and contribute to water quality and healthy aquatic ecosystems. The research will also identify heritable physiological traits that may enable future hybrid poplar plantations across a broader range of environments, and the selection of poplars suitable for environmental reclamation.