152 MATERIALS AND METHODS Tree Propagation and Growth In June 2001, 30 cm softwood cuttings of Acer × freemanii ‘Armstrong’ and Acer rubrum ‘Brandywine’ were collected from Klyn Nurseries, Inc., Perry, Ohio, U.S. ‘Armstrong’ is commonly used in street and landscape plantings throughout much of the northeast United States for its excellent autumn color and up- right habit (Sydnor and Cowen 2000), and ‘Brandywine’, new to the market, has good autumn color, and is a small stature maple. Cuttings were stripped to 3–4 terminal leaves with 2–4 in- ternodes, trimmed to 20 cm length, kept moist, dipped in a talc formulation of 3000 ppm indole-3-butyric acid (IBA) (OHP, Inc., Mainland, Pennsylvania, U.S.), and set in flats of soilless media (Metro-mix 510, Scotts Company, Marysville, Ohio, U.S.). Cuttings were placed in a continuous-mist house until rooted, and then potted in #250 classic black pots impregnated with Root Right [Migratrol (active ingredient: cuprous chloride, 5.6% w/w), Chambersburg, Pennsylvania, U.S.] using the same media. These were grown in a glass greenhouse with day and night temperature set points of 24°C and 21°C, respectively. Af- ter three weeks, trees were fertilized once a week until leaf drop with 100 mg·L-1 N from 20N-4.3P-16.7K water-soluble fertil- izer (Peter’s 20-10-20, O.M. Scotts Co., Marysville, Ohio, U.S.). Pot Construction Schedule 40 standard polyvinyl chloride (PVC) pipe was used to construct 30.5 cm inner diameter (ID) by 38 cm deep pots. PVC plastic sheeting (0.3 cm thick) was glued to the bottom of the cut pipes using PVC glue. A 1.9 cm hole was drilled in the side of each pot, 3 cm from the base and a plastic pipefitting was glued into each hole. A 1.9 L plastic container (Gladware Products Com- pany, Oakland, California, U.S.) was attached to each fitting to serve as the water reservoir, or nonweighing lysimeter. Containers were covered with 0.9 mL black plastic to prevent algal growth. Subsoil (B horizon) used as the potting medium was ob- tained from Waterman Research and Education Facility in Co- lumbus, Ohio, U.S. (Latitude 40.01° and Longitude -83.04°). The USDA Soil Conservation Service (SCS) classified the soil as Crosby silt loam, fine, mixed, mesic, aeric Ochraqualf type (McLoda and Parkinson 1980). In an undisturbed Cros- by silt loam, the A horizon (down to ~23 cm) is characterized as a silt loam. Below 23 cm, the B and C horizons would be clay loam or silty-clay loam (McLoda and Parkinson 1980). Rocks/stones >16 cm2 were removed and the soil was air- dried for two weeks. Initial water content was then determined. Soil was pulverized and passed through a 2 mm round-hole sieve, and the Bouyoucos hydrometer method was used to determine soil texture, following methodology of Gee and Bauder (1986). . These target bulk densities were selected because they were within the range found by many researchers to affect cer- ©2012 International Society of Arboriculture Soil Compaction After air drying and texture assessment of the soil, water was added to increase gravimetric water content to 15%. Soil was placed in an airtight container and allowed to equilibrate over- night, then weighed and added to pots in three 10.2 cm deep lifts (layers) to obtain target bulk densities of 1.4, 1.6, and 1.8 g·cm-3 Fair et. al: Characterization of Compacted Subsoil and its Effects on Two Maples tain characteristics of tree growth (Alberty et al. 1984; Pan and Bassuk 1985; Masle and Passioura 1987; Cook et al. 1996; Day et al. 2000; Montagu et al. 2001). A 4.5 kg sledgehammer was dropped from a height of about 0.3 m until each lift was at the correct depth to obtain the target bulk density. A soil knife (tool similar to a hand trowel) was used to score each lift to mini- mize formation of an interface between layers. Fourteen pots per target bulk density were prepared. Pots were watered thor- oughly after compaction, covered tightly with plastic, and left to equilibrate for five days. One pot of each bulk density treat- ment was prepared as stated, but left fallow to assess evapora- tion loss from soil. These evaporation measurements were used to correct tree water use, thereby calculating tree transpiration. Three gas ports were created in each of three pots of each of the three target bulk densities. Two 1.3 cm holes were drilled horizontally into the side of each of these nine PVC pots, passing through pot and soil, and one drilled vertically through soil only. Of the horizontal holes, one was drilled at 8 cm below the soil surface, the second at 20 cm below the soil surface, above the water table (saturated soil at bottom 5 cm of pot, created by lysimeter water level). The vertical hole was positioned at about 3 cm from the original root ball and ap- proximately 7 cm from the edge of the pot. Plastic tubing, 0.5 cm ID (Fisher Scientific Company, Pittsburgh, Pennsylvania, U.S.) was inserted into each hole, a rubber sampling septum attached, and wrapped with aluminum foil to prevent drying. The first gas samples were taken 14 weeks after planting with sampling performed every two weeks thereafter to measure O2 CO2 , A flame ionization detector used for ethylene. Oxygen was analyzed on a 100 cm × 0.6 cm column of molecular sieve 5A, and CO2 , N2 , and CO2 , and ethylene gas production. Gas analysis was conducted using a Model 436 Chromepack capillary gas chromatograph (Packard Instrument B.V, Zurich, Switzerland) set at 150°C. A thermal conductivity detector was used for O2 . T (Waters, Milford, Massachusetts, U.S.) column with a he- lium carrier gas at 20 mL·min-1 . Data were processed using a Chroma- topac CR501 (Shimadzu Corporation, Kyoto, Japan). A 1 mL syringe was used to obtain the samples from each gas port. Tree Planting Twenty-one trees per cultivar were used; seven trees of each cul- tivar were planted under each of the three soil density treatments on March 22, 2002. The planting hole was made using a stan- dard golf-green cup-cutter (10.8 cm). A soil knife was used to score the sides of the holes to minimize a potential soil interface. Once planted, pots were placed on greenhouse benches in a com- pletely randomized design. Fabric discs were placed on the soil surface of each pot to minimize evaporation. Initial height and caliper were measured on this date. At the start of experiment, caliper ranged from 0.5 to 0.8 cm and 30 to 60 cm in height. Tree Watering, Measurement, and Overwintering Water was supplied from the bottom by individual lysim- eters that were filled to 1.5 L and replenished daily. The re- plenished volume was recorded as use for that period. Tran- were separated on a 50 cm × 0.6 cm Porapak . Ethylene was separated on an 80–100 mesh alumina (Coast Engineering, Redondo Beach, California, U.S.) column (50 cm × 0.6 cm) with N carrier gas at 60 mL·min-1
July 2012
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