Arboriculture & Urban Forestry 45(3): May 2019 Table 1. Ash (Fraxinus) species, cultivar, and diameter at breast height (dbh ± standard error) of trees at the start of the 2015 growing season in Wooster, Ohio, U.S.A. Ash species Green, F. pennsylvanica White, F. americana Black, F. nigra Blue, F. quadrandgulata Manchurian × black, Cultivar Patmore Autumn Purple Fall Gold seedling origin F. mandshurica × F. nigra Manchurian, F. mandshurica seedling origin Sample size Mean dbh (cm) 8 8 8 8 Northern Treasure 8 8 3.91 ± 0.71 1.38 ± 0.07 4.02 ± 0.31 1.98 ± 0.16 1.56 ± 0.16 1.90 ± 0.10 (158°F) for seventy two hours, recorded dry mass (g) with a semi-micro analytical balance (Mettler Toledo AT 261, Artisan Scientific Corp., Champaign, Illi- nois), ground them with a Wiley mill to pass 40-mesh, and stored them in airtight containers until analysis by the Service Testing and Research (STAR) Labora- tory at the Ohio State University for N concentration. We calculated specific leaf area (SLA) as LA/dry mass (cm2 (mg/g) and leaf area (mg/cm2 We measured leaf gas exchange traits from one leaf on each of the 48 trees on four dates (Figure 1) between 10 am and 12 pm, including net CO2 ilation rate (A, μmol mol-2 (gs, mmol m-2 s-1 s-1 ), intercellular CO2 87 ), stomatal conductance concentration (Ci assim- , μmol CO2/mol air), variable fluorescence (Fv’/Fm’, efficiency of energy harvested by open photosystem II reaction centers), and the fraction of photons absorbed by photosystem II that are used for photo- synthesis (ɸPSII). Measurements were made on an east-facing, fully expanded terminal leaflet with a portable photosynthesis system (LI-6400, LI-COR® , Lincoln, Nebraksa). On each of the four sampling dates, photosynthetic nitrogen use efficiency (PNUE) was calculated as A/N per unit LA (μmol mol-2 s-1 ). Temperature and precipitation were recorded throughout the growing season by a weather station located immediately adjacent to the common garden. Weather data were recorded by the National Oceanic and Atmospheric Administration (NOAA) and made available to the public (www.ncdc.gov). /g), and foliar nitrogen on a dry mass ) basis. Data Analyses We conducted all data analyses in R, version 3.1.1 (R development Core Team 2015). For all linear or gen- eralized linear models (package = stats), appropriate error distributions were chosen based on the shape of the frequency distribution of the response variable. Figure 1. Precipitation (gray bars) and minimum (dotted line) and maximum (solid line) temperatures during the 2015 growing season in Wooster, Ohio. Arrows indicate dates on which gas exchange physiological measurements of ash trees were taken. ©2019 International Society of Arboriculture
May 2019
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