186 Percival and Fraser: Film-Forming Polymers Reduce Salt Spray Injury more stable and nontoxic to leaf tissue. Several studies have found these film-forming polymers to be effective in reducing salt and freezing damage to crop plants of economic signifi- cance (Fuller et al. 2003). Whether applications of these newly developed polymers can improve the salt tolerance of urban trees remains untested. MATERIALS AND METHODS Plant Material and Experimental Design The experiment used 3-year-old, bare-rooted stock of ever- green oak (Quercus ilex L.) laurel (Prunus laurocerasus L.). Trees were planted directly into the ground by hand in early November 2002 and left to establish throughout the 2003 growing season (April through September). The trial site was located at the University of Reading Shinfield Experimental Site, Berkshire. Planting distances were 1 × 1m(3.3 × 3.3 ft). Supplementary irrigation was applied during the 2003 grow- ing season and trees were fertilized in early May 2003 by a broadcast application of granular N:P:K (29:7:9) fertilizer (Bartlett BOOST; The Doggett Corporation, Lebanon, NJ) applied at 40 g/m2 (1.4 oz/11 ft2). The soil was a sandy loam containing 4% to 6% organic matter, pH of 6.2; available P, K, Mg, Na, and Ca were 52.0, 659.1, 175.2, 49.4, and 2188 mg/L (0.0001, 0.005, 0.002, 0.0001, 0.02 oz/gal), respec- tively, at the time treatments began (November 2003). Weeds were controlled chemically using glyphosate (Roundup; Green-Tech, Sweethills Park, Nun Monkton, York, U.K.) from the day of planting, November 2002, to the cessation of the experiment, March 2004. One week before the trial trees were inspected and only those rated with a leaf visual index of zero (no leaf necrosis or foliar discoloration observed) were used in the trial. The experimental design was a ran- domized complete block with five single tree replications per treatment. To keep the physiological age of the leaves com- parable throughout the experiment, measurements of chloro- phyll fluorescence and chlorophyll content (SPAD) were made only on fully expanded leaves present at the com- mencement of the trial. Before film-forming polymer sprays, polythene screens 1 m (3.3 ft) high were erected around each tree to prevent dispersal of sprays and possible cross-contact with other trees and the base of the tree was covered with a 0.5 m × 0.5 m (1.65 × 1.65 ft) polythene mulch to prevent percolation into the soil. Film-Forming Polymers Foliar sprays of the film-forming polymers Bond (active in- gredient [a.i.] alkyl phenyl hydroxyl polyoxyehtylene), New- man Crop Spray 11E™ (a.i. paraffinic oil), Nu-Film P (a.i. poly-1-p menthene), and Spray Gard (a.i. di-1-p menthene) were applied until runoff using a hand sprayer at a concen- tration of 10 (0.3) and 20 mL (0.6 fl oz) per liter (0.26 gal) of water. All film-forming polymers were obtained from United Agri Products Ltd., Alconbury Weston, Huntingdon, U.K. ©2007 International Society of Arboriculture Trees were sprayed on 1 November 2003 and 15 trees per polymer treatment were used. Salt Treatments To assess the longevity and durability of each polymer on the leaf surface at week 1 (7 November 2003), month 1 (7 De- cember 2003), and month 3 (7 February 2004) after polymer application, trees were foliar-sprayed with a 60 g (2.1 oz) sodium chloride per liter (0.26 gal) distilled water solution (6% NaCl solution) until runoff. Five different trees were sprayed with salt at each time interval. Chlorophyll Fluorescence Fluorescence values were obtained by placing leaves in dark- ness for 30 min and attaching light exclusion clips to the leaf of whole trees and chlorophyll fluorescence was measured using a HandyPEA portable fluorescence spectrometer (Han- satech Instruments Ltd., King’s Lynn, U.K.). Measurements were recorded up to 1 sec with a data acquisition rate of 10 s for the first 2 ms and of 1 ms thereafter. The fluorescence responses were induced by a red (peak at 660 nm) light of 1500 mol/m−2/s−1 photosynthetically active radiation inten- sity provided by an array of six red light-emitting diodes. A photosynthetic performance index (PI) based on an equation that combines the relationship of calculated relative 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 transport (0) i.e., RC/ABS × po/(1-po) × 0/(1 − 0; Clark et al. 1998, 2000) were used to quantify any effects on leaf tissue. PI values have been shown to be a highly sensitive measure of leaf photosynthetic activities as an indirect measure of plant vitality (Percival and Fraser 2001). PI values were automati- cally calculated by the HandyPEA. Measurements were made at day 14 after salt treatment at each time (week 1, months 1 and 3) interval. Chlorophyll Measurements A Minolta chlorophyll meter SPAD-502 (Spectrum Tech- nologies, Inc., East Plainfield, IL, U.S.) was used. Chloro- phyll was measured at the midpoint of the leaf next to the main leaf vein. Calibration was obtained by measurement of absorbance at 663 and 645 nm in a spectrophotometer (PU8800 Pye Unicam; Fisher Scientific UK Ltd., Loughbor- ough, Leicestershire, U.K.) after extraction with 80% v/v aqueous acetone (regression equation 5.80 + 0.057x; r2 adjusted 0.82, P < 0.01) (Lichtenthaler and Wellburn 1983). Measurements were made at day 14 after salt treat- ment at each time (week 1, months 1 and 3) interval. Leaf Necrosis Leaf necrosis was assessed visually at day 14 after salt treat- ment. Each tree was rated ona0to5 rating scale using a visual indexing technique and ratings on the scale: 0 no
May 2007
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