Arboriculture & Urban Forestry 38(4): July 2012 spiration rate was calculated for the season and per unit leaf area. Transpiration measurements began May 31, 2002, and continued until leaf removal in October 2002. On October 19, 2002, final height and caliper were measured. All leaves were harvested from each tree to determine leaf area, after which leaves were placed in a drying oven at 82°C until dry. Two trees were randomly selected from each cultivar for each soil compaction level for destructive harvest in October 2002. Stems were cut at top of root plate. Root volume was determined using a variation on the water-volume displacement method of Harrington et al. (1994) (Figure 1). A 10-L pipette cleaner (Na- lgene°, Rochester, New York, U.S.) was used as the water tub. It was filled with 6 L of water. A small hole was drilled 35 cm from the base of the pipette cleaner. A fitting was placed in the hole and 0.6 cm flexible plastic tubing was attached to the fitting. A 2 mL pipette, measuring to 0.01 mL was attached to the other end of the tubing. This was mounted alongside the pipette cleaner. The zero mark on the pipette was positioned level with the meniscus of the water in the tub. The tub and pipette were then calibrated by adding 1 L of water. This procedure was performed several times to ensure accurate calibration. Each time 1 L of water was added, the amount of water displaced was determined by count- ing the number of 0.01 mL increments the water level rose in the pipette. The volume of water displaced in the pipette by a known volume of water was used as a calibration factor to calculate root volume. Tree roots were soaked in water for approximately 15 minutes prior to volume determination. Each root system was gently dried, and then balled tightly to ensure the root system would float freely. The pipette was zeroed and the roots were dipped into the tub and, after the water came to rest, a reading was recorded. The root ball was suspended above the tub for ap- proximately three minutes or until dripping had ceased. The roots were gently shaken to remove any excess water. Three readings were taken for each root system. Mean volumes were determined by multiplying the reading by the calibration factor. Stems and roots were placed in drying oven at 82°C until dry, about one week. Trees not harvested (n = 15 of each species) were over- 153 wintered in a minimum heat polyhouse with mean days/nights of 25°C and 4°C, from November 15, 2002 through April 10, 2003. On April 10, 2003, the overwintered trees were returned to ran- dom locations on greenhouse benches and the lysimeters recharged. Tree height and caliper were measured on this date. Transpiration measurements (collected as described earlier) began April 15, 2003. On October 16, 2003, leaves were harvested from all re- maining trees, leaf area measured, and dried as in the previous year. Final tree height and caliper were measured. A random sample of three trees from each cultivar and each soil compac- tion treatment was selected for destructive harvest. Root vol- ume was determined as previously explained, as were stem and root dry weights. The remaining trees (n = 6 of each spe- cies) were overwintered, as before, on November 22, 2003. In the final year of the study, the remaining trees were re- turned to greenhouse benches on March 23, 2004. Tree height and caliper were measured on this date. Lysimeters were re- charged and transpiration measurements began March 29, 2004. As with before, leaves were harvested from all remain- ing trees on August 30, 2004. Height and caliper were mea- sured on August 31, 2004. The remaining trees were de- structively harvested and stem and root dry weights, and root volume were determined as described previously. Soil Measurements Two intact soil cores, 4.7 cm ID by 4.8 cm length were removed from each PVC pot in which a tree had been harvested, with an AMS Slide Hammer (Ben Meadows Co., Janesville, Wiscon- sin, U.S.). Excess soil was carefully trimmed from the ends of each core and cores were weighed. The excess soil was placed in metal tins, weighed and dried at 105°C for ~24 hours to de- termine the gravimetric water content (Blake and Hartge 1986). Upon completion of testing, cores were oven dried and weighed to calculate bulk density (ρb). From ρb and known water gravi- metric content, air-filled porosity (AP), total porosity, and void ratio were determined based on their mathematical relationship to ρb and water content for a known sample size. Saturated hy- draulic conductivity (Ks) was measured in 2002 and 2003 for the intact cores following methodology of Klute and Dirksen (1986). Experimental Design and Data Analysis Pots and compaction treatments were arranged on greenhouse benches in a completely randomized design. Data were analyzed using SAS's general linear model procedures (PROC GLM), and correlations determined using PROC CORR to assess differences and trends between particular soil parameters and tree growth vari- ables (SAS Inst., Inc., Cary, North Carolina, U.S.). Multiple com- parisons were made using Tukey's honestly significant difference (HSD, a = 0.05). The Ks measurements were found to be well de- scribed by a log-normal distribution; the logarithmic-transformed Ks values were then analyzed using GLM and Tukey's HSD. RESULTS AND DISCUSSION Figure 1. Adaptation of water displacement tub to assess root vol- ume (Harrington et al. 1994). Roots were hung from center clip and allowed to float, unhindered in water. Water displaced was measured in pipette with use of magnifying glass. The system was calibrated three times before assessing root volumes, and each root system was assessed three times to obtain average volume. Soil Assessment The textural analysis classified the subsoil as a clay loam with 24% sand, 37% clay, and 39% silt. The target ρb levels were 1.4, 1.6, and 1.8 g·cm-3 ©2012 International Society of Arboriculture , respectively. The actual mean ρb val-
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