Growth and Physiology Vary Little Among North American, an Asian, and a North American x Asian Hybrid Ash in a Common Garden in Ohio, U.S.A

Abstract

The emerald ash borer (EAB) (Agrilus planipennis Fairmaire) invasion of North America has increased interest in ash (Fraxinus, Oleaceae) phylogeny, ecology, and physiology. In a common garden in central Ohio, we compared the performance of three North American ash cultivars that are highly susceptible to EAB (F. pennsylvanica ‘Patmore,’ F. americana ‘Autumn Purple,’ and F. nigra ‘Fall Gold’), one North American species that is less susceptible to EAB (F. quadrangulata), and two taxa that are resistant to EAB (F. mandshurica and F. mandshurica × F. nigra ‘Northern Treasure’). During the 2015 growing season, we measured diameter growth, foliar N concentration, specific leaf area, and on four dates (two with adequate and two with low precipitation) we measured CO2 assimilation rate (A), stomatal conductance (gs), intercellular CO2 concentration (Ci), photosynthetic nitrogen use efficiency (PNUE), variable fluorescence (Fv’/Fm’: efficiency of energy harvested by open photosystem II reaction centers), and the fraction of photons absorbed by photosystem II that were used for photosynthesis (ɸPSII). F. pennsylvanica grew fastest and on most sampling dates was superior in physiological performance (A, gs, and ɸPSII). Generally, however, there was little interspecific variation in growth and physiology among the different ash taxa tested, as all performed well. This suggests that the EAB-resistant F. mandshurica and F. mandshurica × F. nigra hybrid, as well as the moderately resistant blue ash, are as physiologically well-suited to growing conditions in the Midwestern United States as green and white ash cultivars that had been widely planted prior to the EAB invasion.