Arboriculture & Urban Forestry 45(3): May 2019 RESULTS Total annual precipitation (rainfall) in 2015 was 93 cm (36.5 inches). Mean minimum temperature was 4°C (39°F) and mean maximum temperature was 17°C (62.5°F). The 1981 to 2010 climate means were sim- ilar: total precipitation (rainfall) = 102 cm (40 inches), mean minimum temperature = 4°C (39°F), and mean maximum temperature = 16°C (60.5°F). Precipitation was adequate for the first two sampling dates and low for the final two sampling dates (Figure 1). In 2015, there were significant differences in diam- eter growth among some ash taxa (F = 2.83; df = 5.41; P = 0.030). Diameter growth was greater for green ash than for blue, white, or Manchurian × black ash (Figure 2a). Diameter of trees prior to the start of the 2015 growing season did not vary significantly by taxon (F = 0.07; df = 1.41; P = 0.790). There were no differences in SLA among ash taxa (Figure 2b; χ2 = 0.34; df = 5.41; P = 0.764). Nitrogen per unit LA was lower in blue ash than in the other taxa and lower in white ash than in Manchurian ash (Figure 2c; χ2 = 0.56; df = 5.41; P < 0.001). SLA was highly positively correlated with leaf N on a leaf area basis (r ≥ 0.93; P < 0.001) in all ash taxa except the Manchurian × black ash hybrid (r = 0.67; P = 0.100) (Table 2). SLA and leaf N were not cor- related with diameter growth in most taxa. The excep- tion was that diameter growth was correlated with leaf N in Manchurian ash (r = 0.74; P = 0.038) (Table 2). There was a significant interaction between the effects of taxon and date on A (F = 2.88; df = 15,124; P < 0.001), which was greater for green ash than some other species on 22 Jun, all other species on 27 Jul and 7 Sep, and only blue ash on 24 Aug (Figure 3a). A of blue ash was lower than all the other ash taxa on 24 Aug. There was a significant interaction between the effect of taxon and date on gs df = 15,124; P < 0.001); gs (F = 5.10; of green ash was greater than the other species on 22 Jun and 27 Jul, did not differ from other taxa on 24 Aug, and was greater than blue, black, and the Manchurian × black ash hybrid on 7 Sep (Figure 3b). There also was a signif- icant interaction between taxon and date for PNUE (F = 2.08; df = 15,124; P = 0.015). PNUE of green ash was greater than that of black ash on 22 Jun (Fig- ure 3c). On 27 Jul, however, PNUE of green and blue ash did not differ, but both were greater than that of Manchurian ash, and PNUE of blue ash was greater 89 than that of white ash (Figure 3c). On 24 Aug, there were no differences in PNUE among the ash taxa (Figure 3c). On 7 Sep, PNUE of green ash was greater than that of Manchurian, but no other comparisons were different (Figure 3c). Taxon and date had signif- icant but not interacting effects on ɸPSII (species: F = 16.20; df = 15,124; P < 0.001, date: F = 22.14; df = 15,124; P < 0.001). ɸPSII of green ash was greater than the other taxa on all dates, which was largely influenced by the difference between green ash (mean = 0.20) and the other taxa on 7 Sep (Figure 3d). ɸPSII was lower on 24 Aug than on 22 Jun and 27 Jul (means ≤ 0.14). ɸPSII on 7 Sep was not different than on the other sampling dates. Correlations between measures of growth and physiology were not consistently significant, either by date or by ash taxa (Tables 2–5). Diameter growth was not significantly correlated with physiological measures on 22 June (soil moisture high) (Table 2), but was significantly correlated with some leaf vari- ables for some taxa on 27 July (soil moisture still high). For example, Fv’/Fm’ was significantly cor- related with growth for white ash (r = 0.79; P = 0.019) and Manchurian ash (r = 0.77; P = 0.024) (Table 3). On 24 Aug (precipitation was low), Ci was correlated with growth for green ash (r = 0.77; P = 0.025), and A and PNUE were both correlated with growth for Manchurian ash (r = 0.71; P = 0.050 and r = 0.86; P = 0.001 for A and PNUE, respectively) (Table 4). On 7 Sep (precipitation was low), A was correlated with growth for green ash (r = 0.73; P = 0.040); ɸPSII was correlated with growth (r = -0.78; P = 0.022) for white ash; and A, Ci with growth for Manchurian ash (r = 0.72; P = 0.046, r = -0.72; P = 0.047, r = 0.73; P = 0.041 for A, Ci ɸPSII, respectively) (Table 5). , and ɸPSII were all correlated , and . On most sampling dates, A was positively cor- related with gs correlated with gs Some measures of physiology were generally cor- related with one another. Among all sampling dates, PNUE was often negatively correlated with leaf N and SLA, and gs Ci was often correlated positively with and PNUE, and PNUE was positively , especially for black, Manchurian, and Manchurian × black ash. On 7 Sep when precipi- tation was low, more frequently among taxa than on the other sampling dates, ɸPSII was correlated with A, PNUE, and gs (Table 5). (if significant, r ≥ 0.71; P ≤ 0.050) ©2019 International Society of Arboriculture
May 2019
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