PS 7-86 - Transgenerational plasticity and genetic variation contribute to varied climate response in black cottonwood common gardens

Abstract: Climate change is causing forest tree distributions to shift. Changing weather patterns can impact the survival of plants which, in turn, determines whether a plant species will continue to survive into the future. Populations can persist via genetic variation and trait evolution as well as phenotypic plasticity through transgenerational epigenetic inheritance. Phenotypic plasticity provides a faster way to cope with environmental change than populations evolving genetic adaptation to novel environments. Populus trichocarpa, black cottonwood, is an important riparian species on the Northwest coast from California to British Columbia. We tested whether both genetic variation and transgenerational plasticity would contribute to variation on performance in a novel climate. Clonal cuttings of black cottonwood were obtained from six locations that extended across the species distribution range in the Northwestern United States and British Colombia. Replicate clones were planted in two common gardens in Oregon, USA with contrasting climatic conditions. Replicated clones planted across the two gardens in Oregon were the treatments to test for plasticity induced by environmental variation that may passed to clonal offspring. After ten years, we took clonal cuttings from the first-generation planting gardens in Oregon and planted them in two second-generation gardens in Arizona to observe if the inheritance of survival and growth characteristics is due to transgenerational plasticity or genetic variations. On average, mortality differed for clones taken from different first-generation environment gardens in Oregon when planted in the two gardens in Arizona. Second-generation offspring growth in Arizona was greatest when clones were originally harvested from the Oregon field collected genetic sources and planted in the first-generation garden at Corvallis, Oregon. Our results show an overall interaction between the field collected genetic source environment temperatures and the environments of the first-generation gardens in Oregon. The results from this study conclude that there is support for both genetic and epigenetic forces impacting the survival and growth of black cottonwoods in a common garden experiment. If we are to maintain the black cottonwood population density, plasticity may help slow climate related decline for the southernmost populations as they would face extirpation northward. This would cause the northern populations to decline or face extirpation themselves but be slowly replaced by southern populations with the genetic and epigenetic traits needed to survive the novel environment.