Arboriculture & Urban Forestry 32(6): November 2006 279 tive number of reaction centers (RC) per energy absorbed (ABS) and then multiplied by two expressions describing the yields of light trapping (po) and subsequent electron trans- port (0), i.e., RC/ABS × po/(1 − po) ×0/(1 −0; Clark et al. 1998, 2000; Percival and Fraser 2001) were used to quantify any effects on leaf tissue. PI values have been shown to be a highly sensitive measure of leaf photosynthetic ac- tivities as an indirect measure of plant vitality. PI values were automatically calculated by the HandyPEA. For experiment 1, leaf chlorophylls a and b and carotenoids (lutein, -carotene, neoxanthin, -carotene, zeaxanthin, an- theraxanthin, violaxanthin) were analyzed using a high- performance liquid chromatography (HPLC) system (Schin- dler and Lichtenthaler 1994). Leaf samples were excised from trees and immediately placed in liquid nitrogen. Thirty leaf samples per treatment, i.e., five leaves per tree, were taken. Pigment analysis was performed on the next day. Pig- ments were extracted from leaves with 100% aqueous ac- etone (quartz sand mortar) and separated and quantitatively determined by reverse phase HPLC applying a Nucleosil C18 column (particle size 4 m). The solvent systems for the combined isocratic and gradient separation and quantification were acetonitrile–methanol–0.2 M tris/HCL buffer and methanol–hexane (Lichtenthaler et al. 1992). For experiment 2, for comparative reasons and fast throughput of samples, chlorophyll a and b were extracted from leaf samples by suspending 1 g (0.035 oz) of fresh tissue in 5 mL (0.15 fl oz) 80% v/v aqueous acetone. After cen- trifugation in closed vials, an aliquot of the supernatant was transferred to a 1 cm (0.4 in) path glass cuvette and chloro- phylls a and b calculated according to the equations of Licht- enthaler and Wellburn (1983) following measurement of ab- sorbance at 663 and 645 nm in a spectrophotometer (PU8800 Pye Unicam). Leaf necrosis was assessed visually. Each tree was rated on a 0 to 5 rating scale using a visual indexing technique and ratings on the scale: 0no necrosis observed; 1less than 5% of leaves affected and no aesthetic impact; 2 5% to 20% of leaves affected with some yellowing but little or no defoliation; 3 21% to 50% of leaves affected, significant defoliation, and/or leaf yellowing; 451% to 80% of leaves affected, severe foliar discoloration; and 5 81% to 100% of foliage affected with 90% to 100% defoliation. At the conclusion of experiment 2 (week 8), trees were destructively harvested and leaf, shoot, and root dry weight recorded after oven drying at 85°C (185°F) for 48 hr. Leaf areas were quantified using a Delta-T area meter. The results from the experiment were statistically analyzed using Genstat 5; significant differences from controls (non- sugar-treated trees) at the 95% confidence level (P > 0.05), were tested for using analysis of variance (ANOVA) follow- ing checks for normality and equal variance distributions were met (Bartlett test). The comparisons of means of indi- vidual treatments were made by calculating t values from the SED. Data for each tree species were analyzed separately. Recovery from salt-induced damage was quantified using correlation equations and coefficients of determination (r2) calculated using the curve-fitting feature of SlideWrite using quadratic polynomial regression analysis. RESULTS Experiment 1: Prevention of Salt-Induced Damage by Prior Application of Sucrose At day 15 after salt application, leaf chlorophyll fluorescence PI and total chlorophyll values were between 38% and 58% higher in English oak and 33% to 57% and 14% to 27% higher in holly, respectively, pretreated with sucrose at 30 and 60 g (1.1 and 2.1 oz) (Tables 1 and 2). Likewise, leaf necrosis was reduced by 33% to 57% in English oak and by 30% to 68% in holly when trees were pretreated with sugars (30 and 60 g [1.1 and 2.1 oz]), compared to trees treated with salt only, at 30 and 60 g (1.1 and 2.1 oz) per liter of water (Tables 1 and 2). Such responses in sugar-treated trees indi- cate less impairment of the leaf photosynthetic integrity, im- proved photosynthetic efficiency, and reduced degradation of the chlorophyll molecule structure compared with water- treated controls. No marked differences were recorded be- tween species in response to salt treatment only with similar PI (2.17 to 4.45) and leaf necrosis (3.4 to 4.2) values recorded (Tables 1 and 2) at day 15 after treatment. Leaf carotenoid (lutein, -carotene, neoxanthin, -carotene) and xanthophylls (zeaxanthin, antheraxanthin, and violaxanthin) were ≈30% to 60% higher in sucrose-treated trees compared with no su- crose-treated trees irrespective of species at the cessation of experiment 1 (day 15). Maximal increases in total carotenoids (carotenoid + xanthophylls) were found in trees after appli- cation of sucrose at 25 g (0.9 oz) per liter of water followed by 30 g (1.1 oz) NaCl at day 3 after sucrose treatment. None of the treatments used in this investigation altered the ratio of chlorophyll a:b in English oak (2.99 to 3.21) or holly (3.22 to 3.45; Tables 1 and 2). Irrespective of species, there were no significant differences in leaf area, root, shoot, leaf, or total plant dry weight at day 15 after treatment (data not shown). Experiment 2: Effects of Sucrose on Recovery From Salt Damage The pattern of recovery 2 weeks after salt application in PI, leaf chlorosis, and chlorophyll content is shown for English oak and holly (Tables 3 and 4). At 2 weeks after salt treatment, all three parameters began to recover irrespective of treatment (with or without sucrose). Consequently, the pattern of re- covery was quantified by quadratic regression analysis to compare the rate of recovery from week 2 until the cessation ©2006 International Society of Arboriculture
November 2006
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