Journal of Arboriculture 31(1): January 2005 11 separated by rows of guard trees at 0.5 m (1.65 ft) spacings. Within each plot, one of nine fertilizer treatments was used per species, along with a nonfertilized control: • Ca nitrate (Ca(NO3 Ltd, Immingham, N.E, Lincolnshire, UK), applied at 20, 40, and 80 g/m2 )2 • Ca nitrate borate (Ca(NO3 Nitrabor™ (Yara UK Ltd, Immingham, N.E, Lincolnshire, UK), applied at 20, 40, and 80 g/m2 (0.07, 1.4, and 2.8 oz/ft2 )2 H3 BO3 • high-nitrogen fertilizer (N:P:K = 24:7:7, trade name Bartlett BOOST, The Doggett Corporation, Lebanon, NJ) applied at 20, 40, and 80 g/m2 Table 1. Physical characteristics of evergreen oak (Quercus ilex) and holly (Ilex aquifolium) after grading. Attribute Height (cm) Girth (cm) Height:girth ratio (cm/cm) Shoot and leaf dry weight (g) Root dry weight (g) Shoot:root ratio (g/g) Root area (cm2 ) Holly 46.3 (2.20)* 1.56 (0.18) 29.7 (2.08) 4.80 (0.39) 4.10 (0.38) 1.17 (0.10) 35.36 (3.02) *Values are mean and standard errors for 10 trees. Thirty evergreen oak and holly were used per fertilizer treatment (i.e., 2 × 9 × 10 = 180 trees per block, 10 trees per plot [90 evergreen oak, 90 holly]; 3 × 180 = 540 trees total). Fertilizers were applied uniformly to all plots by broad- cast on the soil surface. All fertilizers were applied in the fall (4 October 2001) and trees planted by hand at 0.5 m (1.65 ft) spacings 1 week later. The soil was a sandy loam contain- ing 4% to 6% organic matter and had a pH of 6.2. Available P, K, Mg, Na, and Ca were 52, 659.1, 175.2, 49.4, and 2,188 mg/L, respectively. Weeds were controlled chemically using glyphosate (Roundup, Green-Tech, Sweethills Park, Nun Monkton, York, UK) prior to planting and by hand through- out the experiment. No watering was required during the experimental period. Based on results of the 2001 trial, the experiment was repeated in 2002 on the same dates using only four of the nine treatments: Ca(NO3 N:P:K (24:7:7) applied at 40 g/m2 nonfertilized control. Freezing Treatments At months 1, 2, 4, and 8 post-fertilization, two fully ex- panded, nonsenescing leaves per tree, 15 trees per fertilizer treatment (5 trees per block) were excised at the base of the petiole using a razor blade and placed abaxial surface down, in a Petri dish on moist Watman’s filter paper and sealed with a thin polythene film permeable to air but not water, then placed in darkness in a Merck environmental freezing (1.4 oz/ft2 )2 , Ca(NO3 ), and a )2 H3 BO3 , Evergreen oak 45.3 (2.11) 1.52 (0.15) 29.1 (1.98) 4.71 (0.38) 5.16 (0.39) 0.91 (0.08) 40.17 (3.26) , trade name , trade name Tropicote™ (Yara UK ) chamber, where the temperature was reduced by 2°C (3.6°F) per h from 10°C (50°F) to –8°C (18°F). This tem- perature was maintained for 4 h, after which the tempera- ture was raised by 2°C per h to 10°C, a cooling regime representative of a naturally occurring severe frost (Sakai and Larcher 1987). All leaf material was prepared within 2 h of collection from the field. Salt Treatments At months 1, 2, 4, and 8 post-fertilization two fully ex- panded, nonsenescing leaves per tree, 15 trees per fertilizer treatment (5 trees per block) were excised at the base of the petiole using a razor blade. Upon arrival at the laboratory (< 2 h after collection), leaves were immersed in an 8% salt (NaCl) solution for 2 min. After salt immersion, leaves were placed, abaxial surface down, in a Petri dish on moist Watman’s filter paper sealed with a thin polythene film permeable to air but not water. Following all treatments, leaf samples were placed in a Merck environmental growth chamber in darkness at 22°C (72°F) for 72 h, a time after which detrimental effects on chlorophyll fluorescence values could be detected (Greaves and Wilson 1987). Because of the potential influence of leaf removal on total plant dry weights measured at the cessation of the experiment, leaves were taken only from the same 15 trees at months 1, 2, 4, and 8. The remaining 15 undamaged trees were used to obtain dry weight measurements recorded at month 8. Physiological Tests Because leaf chlorophyll fluorescence and SPAD measure- ments are noninvasive and nondestructive, following each measurement the same evergreen oak and holly leaves were used to obtain electrolyte leakage values. All physiological measurements taken at months 1, 2, 4, and 8 were obtained on leaf material present on the plant at the initiation of the experiment (existing leaves). In addition, physiological measurements at month 8 only were also taken from newly formed spring leaf tissue (i.e., new leaves not present at the time of fertilizer application). Chlorophyll Fluorescence Immediately after the freezing treatment and 72 h post- salinity treatments, leaves were adapted to darkness for 30 min by attaching light exclusion clips to the leaf surface. Chlorophyll fluorescence was measured using a HandyPEA portable fluorescence spectrometer (Hansatech Instruments Ltd., King’s Lynn, UK). Measurements were recorded up to 1 s with a data acquisition rate of 10 µs for the first 2 ms and of 1 ms thereafter. The fluorescence responses were induced by a red (peak at 650 nm) light of 1500 µmol m2 /s photosynthetically active radiation (PAR) intensity provided by an array of six light-emitting diodes. The ratio of variable ©2005 International Society of Arboriculture
January 2005
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