A goal of many riparian restoration efforts is to support a healthy, self-sustaining vegetation community. This goal is being challenged by climate change, which is altering temperature and river flow regimes, which determine the structure and composition of riparian vegetation. Riparian plant physiology and growth are influenced by genetically-based adaptation to climate and river flow characteristics. Climate provenance may influence a plant’s flood response due to trade-offs between adaptations to temperature and flood stress. The goal of this study was to examine growth responses of Pluchea sericea (arrowweed) collected from five locations (“provenances”) along the Colorado River in the Grand Canyon, representing average temperatures spanning 17.7 to 22.6 °C. Inside a greenhouse, 250 cuttings were grown for a year, then assigned to different flooding depths ranging from the root crown fully submerged to fully out of the water for a duration of 3 months. All pots sat on PVC tubes filled with sand, which allowed roots to grow, while controlling flood depth. A suite of morphological and physiological traits were measured to characterize plant responses, and Bayesian linear regressions and permutational MANOVA were used to evaluate the effects of provenance, flood depth, and their interaction on these responses.
Results/Conclusions
Regressions of height growth and root weight on flood depth (scaled from -1 to 1) produced effect sizes of -13.8 (-7.0, -20.6) and -2.3 (-1.8, -2.9), respectively, across all provenances. Greater flood depths reduced height growth and root weight (p < 0.001 for both), but increased specific leaf area (SLA, p = 0.02). Individuals from different provenances differed in their height growth, root weight, and SLA (all p < 0.001) when flood depth was accounted for, suggesting some genetic control over these traits. The provenance-by-flood interaction effect was not significant for height growth or SLA (p > 0.05), but was for root weight (p = 0.04). Generally, P. sericea exhibited increased biomass as flood depth decreased across the range of treatment conditions, with the lowest flooding depths yielding the greatest biomass. Climate provenance of P. sericea may have only a weak or partial influence on response to flooding, but is strongly related to morphology. This could allow land managers and restoration practitioners to choose restoration stock based on the climate conditions or morphological traits of the source population without compromising flood adaptation.