Arboriculture & Urban Forestry 33(3): May 2007 187 necrosis observed; 1 less than 5% of leaves affected and no aesthetic impact; 2 5% to 20% of leaves affected with some yellowing but little or no defoliation; 321% to 50% of leaves affected, significant defoliation and/or leaf yellow- ing; 4 51% to 80% of leaves affected, severe foliar dis- coloration; 581% to 100% of foliage affected with 90% to 100% defoliation. The individual ratings for each tree in each treatment were used for statistical analysis. Foliar Sodium and Chloride Analysis Leaf samples (six leaves per tree) were thoroughly washed and then dried in a convection oven at 85°C (185°F) for 48 hr before grinding through a 0.5 mm (0.02 in) cyclone mill (Retsch, Middlesborough, U.K.). Samples (0.5 g) were placed into 150 mL (4.5 fl oz) volumetric flasks and digested in 20 mL (0.6 fl oz) of 7:1 nitric/perchloric acid. After cooling, the solutions were brought to volume with deionized water and analyzed by inductively coupled plasma-emission spectros- copy elemental analysis. Nutrient values were expressed as grams per kilogram dry weight. Measurements were made at day 14 after salt treatment at each time (week 1, months 1 and 3) interval. Plant Height and Leaf Area At the end of the 2004 growing season (23 September), trees were destructively harvested and height recorded by measur- ing the distance from the tip of the leading apical shoot to the soil surface. Leaf areas were quantified using a Delta-T area meter (Delta-T Devices, Ltd., Cambridge, U.K.). Data Analysis Statistical methods were as follows: before the analysis, data were examined to ensure normality and homogeneity of vari- ance (Anderson-Darling test) was met to meet the assump- tions for the analysis of variance. Data were then analyzed as a randomized complete block using an analysis of variance. Differences in levels of leaf necrosis severity, chlorophyll fluorescence, and SPAD readings from control values were determined and means were separated at the P < 0.05 level of significance using the Genstat for Windows program. Species (S) Polymer (P) Time (T) S*P S*T P*T S*P*T Chlorophyll content <0.001 <0.001 <0.001 0.145 0.026 <0.001 0.241 PI <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Leaf necrosis 0.004 <0.001 0.001 <0.010 0.166 <0.001 0.887 RESULTS AND DISCUSSION The influence of species (S), polymer (P), time of salt appli- cation (T), and salient interactions of these three factors on leaf necrosis, PI, chlorophyll content, leaf Na and Cl content, height and leaf area singly and in combination are shown in Table 1. During the study, none of the treated or control trees died as a result of salt spray. Salt damage was recorded on control trees as indicated by leaf necrosis ratings between 3.6 and 3.9 on foliar tissue of evergreen oak and laurel (Tables 2 and 3). Increased salt damage on controls was mirrored by reduced leaf PI and chlorophyll content, elevated leaf Na and Cl con- tent, and reduced height and leaf area (Tables 2 and 3). Irrespective of tree species the film-forming polymers Nu- Film-P and Spray Gard did not provide any significant degree of protection against salt-induced damage irrespective of con- centration (1% or 2%) applied. Chlorophyll concentrations, leaf PI values as a measure of photosynthetic efficiency, vi- sual leaf necrosis (Tables 2 and 3), foliar Na and Cl (Tables 4 and 5), content, and growth (height, leaf area; Tables 6 and 7) did not significantly differ from control values with two exceptions: evergreen oak after application of Spray Gard at 2% where leaf necrosis values were significantly lower (P < 0.05) than controls at week 1 and laurel also after ap- plication of Spray Gard at 1% where leaf area values that were significantly higher (P < 0.05) at month 3. Failure of these two film-forming polymers to provide any form of pro- tection against salt damage is in agreement with other work- ers who also found poly-1-p menthene (Vapour Gard; Miller Chemical & Fertilizer Corp., Hanover, PA, U.S.) and di-1-p menthene (Wilt-Pruf; Wilt-Pruf Products, Inc., Essex, CT, U.S.) -based products ineffective as potential ameliorants to reduce salt spray injury on woody plants (Emmons et al. 1976). Sauer (1980) also found several types of predomi- nantly poly and di-1-p menthene-based film-forming poly- mers ineffective in protecting roadside plants from salt spray injury. However, contrary to previous work (Constantini and Rich 1973; Emmons et al. 1976) phytotoxicity and enhanced leaf Na and Cl contents was not observed in the two test species Table 1. P values for growth and tree vitality post salt treatment. Factor Leaf Na content 0.222 <0.001 <0.001 0.416 0.866 <0.001 0.509 Leaf Cl content 0.216 <0.001 <0.001 0.231 0.467 <0.001 0.778 Height <0.001 <0.001 <0.001 0.456 0.342 0.015 0.461 Leaf area <0.001 <0.001 0.006 0.040 0.011 0.149 0.938 PI photosynthetic performance index; Na sodium; Cl chloride. P < 0.05 significant at the 95% confidence level; P < 0.01, significant at the 99% confidence level; P < 0.05 not significant. ©2007 International Society of Arboriculture
May 2007
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