Arboriculture & Urban Forestry 36(5): September 2010 Scots pine for the first 10 minutes. Fo and Fv/Fm values at sam- pling times 15 and 20 minutes, however, indicated greater detri- mental impacts on foliar tissue of Scots pine compared to ever- green oak (Table 1–4). Such a response indicates Scots pine may be able to better cope with heat stress over a short time period (up to 10 minutes), while evergreen oak superior over a prolonged period of intense heat (10–20 minutes). Irrespective of species, greatest protection of the leaf photosynthetic system to heat in- Table 3. The influence of prolonged temperature ex- posure (50°C) on stability of the chlorophyll a/b light- harvesting complex within photosystem II based on chlo- rophyll fluorescence Fo responses within leaf tissue of Scots pine (Pinus sylvestris). Treatment 0 min 5 min Control 0.15g 0.30g 0.45g 90.3a 89.7a 82.0a 85.8a 152.7a 155.7a 120.0a 127.6a 10 min 15 min 20 min 218c 290.4b 205bc 145a 156a 243.4ab 303a 209.6a 314a 298a 236.2ab 299a Lower case letters indicate significant differences between means for each evalua- tion date by LSD (P = 0.05). All values mean of ten trees, five leaves per tree. Table 4. The influence of prolonged temperature exposure (50°C) on photochemical efficiency within leaf tissue of Scots pine (Pinus sylvestris) based on chlorophyll fluorescence Fv/ Fm responses. Treatment 0 min 5 min Control 0.15g 0.30g 0.45g 0.825a 0.583a 10 min 15 min 20 min 0.429a 0.816a 0.645abc 0.446a 0.818a 0.702c 0.823a 0.680bc 0.595b 0.507a 0.158a 0.194a 0.358c 0.043a 0.067a 0.100b 0.295b 0.056a Lower case letters indicate significant differences between means for each evalua- tion date by LSD (P = 0.05). All values mean of ten trees, five leaves per tree. Table 5. P values for chlorophyll fluorescence Fo and Fv/Fm following penconazole treatment. P < 0.05 are considered significant. Fo Species (S) Concentration (C) S x C <0.001 <0.001 <0.001 Fv/Fm 0.008 <0.001 <0.001 215 duced disorders was achieved by application of penconazole at 30 g per liter of water compared to penconazole applied at 0.15 and 0.45 g per liter of water (Tables 1–4). In this instance all tree vitality measurements were greater than nontriazole-treated con- trols and penconazole applied at 0.15 and 0.45 g per liter of water. Recovery of Containerized Trees from Heat Stress Subjecting containerized trees of both species to 10 minutes at 50°C significantly reduced tree vitality with respect to chloro- phyll fluorescence Fo and Fv/Fm emissions, total foliar chloro- phylls, leaf photosynthetic rates (Pn) and significantly increased damage to cellular membrane integrity as manifest by higher leaf electrolyte leakage and visual leaf necrosis in comparison with non-heat stressed well watered trees (Table 6). There was, however, no significant effect of heat stress on the ratio of chlo- rophyll a/b (Table 6). The influence of penconazole (0.15, 0.30, or 0.45 g per liter of water) applied immediately after heat stress on the pattern of recovery over the following twelve weeks is shown diagrammatically for chlorophyll fluorescence Fo and leaf electrolyte leakage values (Figure 1). The pattern of recovery for these two parameters reflects those recorded for chlorophyll fluorescence Fv/Fm emissions, total foliar chlorophylls, leaf pho- tosynthetic rates (Pn) and visual leaf necrosis (data not shown). Namely, irrespective of treatment (with or without penconazole), all parameters began to recover. Penconazole treated trees were the most capable of recovery (Figure 1). With respect to chloro- phyll fluorescence Fo and leaf electrolyte leakage values recov- ery rates of heat damaged trees treated with penconazole ranged from 20%–50% higher than nonpenconazole-treated control trees (Figure 1). In all cases nontriazole-treated control trees had the least capacity for recovery (Figure 1). Foliar application of penconazole at 30 g per liter of water induced greatest recovery rates over the 12-week period. At Week 12, all values of pen- conazole-treated trees were statistically comparable with well- watered non-heat stressed trees. During the 12 week recovery phase new leaf formation was observed at ca. Weeks 4–6 on both nonpenconazole-treated control and penconazole-treated trees. Application of penconazole had a marked impact on regen- eration from heat stress at the cessation of a 12 week recov- ery period. Regardless of species, height (evergreen oak only), leaf area, root, shoot, and total plant dry weight were, in virtu- ally all instances, significantly (P < 0.05) greater than non- Table 6. The effects of heat stress (50°C) for 10 minutes on alterations to plant physiology of evergreen oak (Quercus ilex) and Scots pine (Pinus sylvestris). Measurements were made 24 hours after the cessation of the heat treatment. Quercus ilex Parameter % electrolyte leakage Fv/Fm Fo Pn Leaf necrosis Chlorophyll a/b Total chlorophylls Nonpenconazole Treated control 26.7b 0.35a 500.6b 2.22a 2.5b 2.92a 40.5a Well-Watered 5.14a 0.83b 225.3a 4.21b 0.0a 3.00a 82.0b % electrolyte leakage, photosynthetic rates (Pn) values mean of 10 trees, two leaves per tree. Fv/Fm, Fo, total chlorophyll (mg/g fresh leaf weight), values mean of 10 trees, five leaves per tree. Leaf necrosis mean of 10 trees. Lower case letters indicate significant differences in rows between means by LSD at (P < 0.05). Pinus sylvestris Nonpenconazole Treated control 32.7b 0.28a 221.3b 1.80a 3.0b 2.81a 22.3a Well-Watered 4.56a 0.81b 92.3a 4.00b 0.0a 2.80a 45.6b ©2010 International Society of Arboriculture
September 2010
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