Journal of Arboriculture 31(2): March 2005 67 phyll and carotenoid concentrations of birch (Betula pendula) following transplanting. MATERIALS AND METHODS Plant Material and Experimental Design Four-year-old, bare-root birch (Betula pendula Roth.), a transplant-sensitive species (Watson and Himelick 1997), were obtained from a commercial supplier in early January and stored at 6°C (42.8°F) in a refrigerated cold store prior to planting. The physical characteristics of 20 trees selected at random from the 1999 and 2003 trials were destructively analyzed to provide an estimation of stock uniformity for each trial were as follows: 1999 Trial • height—91.3 ± 3.7 cm (36.5 ± 1.5 in.) • girth—2.9 ± 0.11 cm (1.2 ± 0.04 in.) • height:girth ratio—31.5 ± 1.01 • shoot dry weigh—19.9 ± 0.99 g (0.7 ± 0.04 oz) • root dry weight—29.3 ± 1.32 g (1.05 ± 0.05 oz) • shoot:root ratio—0.68 ± 0.02 • root area—629 ± 40.93 cm2 (100.6 ± 2.6 in2 ) 2003 Trial • height—17.5 ± 4.76 cm (47 ± 1.9 in) • girth—3.7 ± 0.15 cm (1.48 ± 0.06 in) • height:girth ratio—31.8 ± 1.94 • shoot dry weight—26.3 ± 1.28 g (0.94 ± 0.05 oz) • root dry weight—38.9 ± 1.70 g (1.39 ± 0.06 oz) • shoot:root ratio—0.67 ± 0.02 • root area—786 ± 55.7 cm2 (125.8 ± 8.9 in2 ). Stem diameter was quantified using Mantax blue precision calipers (Haglöf Sweden AB, Langsele, Sweden) at one-third of the height of the stem and girth calculated using the equation C = πD, where C = circumference (girth), π = 3.14, and D = diameter. Root areas were quantified using a Delta-T area meter. Leaf, shoot, and root dry weight were recorded after oven drying at 85°C (185°F) for 48 h. In both 1999 and 2003, the trials were laid out in a randomized complete block design. The block was planned in a square formation to minimize effects of any gradients in soil conditions. Seven treatments (six sugars plus a water- only control), three concentrations, five individual replica- tions per treatment, and two sampling dates (6 × 3 × 5 × 2 = 180 plus 10 controls = 190 trees per trial) were randomized within the block. The same plot was used for both the 1999 and 2003 trials. Trees were planted by hand at the Univer- sity of Reading, Shinfield Experimental Station, Reading, UK, at 2 m (6.6 ft) square spacing on 9 February 1999 and 13 February 2003. Root barriers (RootControl, Green-Tech, Nun Monkton, York) to a depth of 60 cm (24 in.) were installed around each tree in a square pattern at a distance of 1 m (3.3 ft) from the tree to eliminate cross contamina- tion of treatments. The soil was a sandy clay loam containing 4% to 6% organic matter with a pH of 6.2. Weeds were controlled chemically using glyphosate (Roundup) prior to planting, and by hand during the trial. Just prior to planting, all trees had 90% of their root area removed to achieve a root surface area of approximately 60 to 62 cm2 (9.6 to 9.9 in2 ) to simulate field harvesting practices. Two weeks after budbreak (a stage when 80% to 100% of foliage has emerged), which, in this investigation oc- curred on 3 May 1999 and 28 April 2003, a factorial combination of root drenches of six sugars (galactose, rhamnose, sucrose, glucose, fructose, and maltose) at three concentrations (25, 50, and 70 g/L [3.4, 6.8, and 10.3 oz/ gal] of water) were applied. Each tree received weekly for 4 weeks 1.5 L (0.4 gal) of sugar solution applied using a watering can. The spout was lightly rested against the main stem at a height of 30 cm (12 in.), and the sugar solution was allowed to trickle slowly down the main stem. Watering with equal volumes and frequency with water served as the control. Plants received no irrigation or fertilization during the growing season. Chlorophyll Fluorescence Chlorophyll fluorescence was measured at weeks 6 (14 June 1999, 9 June 2003) and 24 (18 October 1999, 13 October 2003) after budbreak. Leaves were adapted to darkness for 30 min by attaching light-exclusion clips to the leaf surface. Chlorophyll fluorescence was measured using a portable fluorescence spectrometer (Hansatech Instruments Ltd., King’s Lynn, UK). Six leaves per tree were selected for measurements (two from the top of the crown, two in the center, and two at the base), and each leaf was tagged to ensure that assessments were taken from the same leaf throughout the entire experiment. Measurements were recorded up to 1 s. The fluorescence responses were induced by a red (peak at 650 nm) light of 600 W/m2 intensity provided by an array of six light-emitting diodes (Shuang and Xu 1999). Fluorescence values recorded include Fv/Fm as a measure of the photochemical efficiency of photosystem II that is widely used in field studies as an early diagnostic measure of plant stress caused by adverse environmental conditions (Meinander et al. 1996). Photosynthetic CO2 The light-induced CO2 Fixation fixation (Pn) was measured in pre- darkened (20 min), fully expanded leaves near the top of the canopy (generally about the fourth leaf from the apex) using an infrared gas analyzer (LCA-2 ADC). The irradiance on the leaves was 700 to 800 µmol/m2 photosynthetically active radiation saturating with respect to Pn; the velocity of the ©2005 International Society of Arboriculture
March 2005
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