Provenance of a Riparian Shrub Changes Traits but Not Flood Response Under a Common Climatic Setting
Emily Palmquist1,2, Kiona Ogle3, Bradley Butterfield4, Thomas Whitham5, Patrick Shafroth6, Gerard Allan7
1 U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, AZ, USA; epalmquist@usgs.gov
2 Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA
3 School of Informatics, Computing & Cyber Systems, Northern Arizona University, Flagstaff, AZ, USA; kiona.ogle@nau.edu
4 Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ, USA; bradley.butterfield@nau.edu
5 Northern Arizona University, Center for Adaptable Western Landscapes (CAWL), Flagstaff, AZ, USA; thomas.whitham@nau.edu
6 U.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO, USA; shafrothp@usgs.gov
7 Northern Arizona University, Center for Adaptable Western Landscapes (CAWL), Flagstaff, AZ, USA; Gerard.allan@nau.edu
The last 20 years of research have shown that flood tolerance and genetically based local adaptation to temperature are key components of riparian plant growth and survival. Climate change and river regulation are altering both climate and flow regimes, such that over the next 20 years, riparian plants will experience simultaneous shifts in temperature and flooding. Within a species, individuals from provenances (places of origin) with differing temperatures can exhibit morphological and physiological variation, but it is unknown if genetically-based variation related to temperature can alter plant responses to flooding. Using a widespread, riparian shrub, Pluchea sericea (arrowweed), we address two hypotheses: 1) Individuals from different climate provenances will exhibit genetically-based differences in their physiological and morphological traits, and 2) Individuals from different provenances will differ in their responses to flooding. Arrowweed cuttings were collected from five provenances along the Colorado River in the Grand Canyon, representing average annual air temperatures spanning 17.3 to 22.6 °C. Inside a greenhouse, one year old cuttings were subjected to different inundation depths ranging from the root crown fully submerged to fully out of the water for a duration of 3 months. A suite of morphological and physiological traits was measured to characterize plant responses, and a subset of individuals (90) was genotyped. Hierarchical, multivariate Bayesian linear regressions were used to evaluate the effects of provenance, flood depth, and their interactions on these responses. When the effect of inundation was accounted for, posterior distributions showed significant differences in many traits among provenances. Models that included both provenance and genotype as random effects were the best models (ΔDIC = -13), suggesting that the combination of climate provenance and genotype partially controls many of these traits. Regressions indicated that greater flood depth reduced final height (mean effect size = -0.1), growth (-0.7), root weight (-1.2), above ground biomass (-1.2), total leaf area (-25.0), and average root diameter (-0.1). While plant size and growth were consistently different across provenances when flood effect was controlled, all provenances and genotypes responded to inundation in a similar manner. This suggests that while both climate provenance and flooding can alter plant traits, interactions between these two factors may not lead to unique provenance or genotype responses to flooding. For this common woody, riparian shrub, managing populations of the next 20 years for specific climate conditions or morphological traits shouldn’t compromise flood adaptations.