204 Struve et al.: Growth and Water Use Characteristics of Oak vious water use research (unpublished data) with oak seed- lings in covered and uncovered containers under greenhouse conditions showed that evaporation represented approxi- mately 5% of evapotranspiration. At the end of each water use period, plant height was recorded. For those studies in which whole plant harvests were done, the following procedures were used. After leaf area was de- termined with leaf area meter (LiCor Model Li 3,100, Lin- coln, NE), roots were washed free of substrate. Root area was determined with a digital image analyzer (Dias II; Decagon Devices, Inc., Pullman, WA, in experiment 1 and with a scanner [Model 5470c scanjet; Hewlett-Packard Co., Boise, ID] and root scanning software [WinRhizo, Version 2002a, Regent Instruments Inc., Canada]) in experiments 2 and 3. Roots from each seedling were separated into two diameter size classes; coarse roots (>2 mm [0.08 in] diameter) and fine roots (<2 mm [0.08 in] diameter). In experiments 2 and 3, a subsample (25% of the total roots) of the fine roots was scanned, whereas all coarse roots were scanned. During scan- ning, the roots were floated in water in a clear plastic tray placed on the scanner. After scanning, root samples were placed into individual bags and oven-dried. The remaining fine roots were placed in a third bag and oven-dried. The total fine root area per seedling was estimated by multiplying the ratio of root area to dry weight of the scanned root sample by the total fine root dry weight. After scanning, seedlings were divided into leaf, shoot, and root tissues and oven-dried at 90°C (194°F) for 96 hr before dry weights were recorded. Individual seedling shoot-to-root ratios were calculated by summing an individual’s leaf and shoot dry weight and di- viding by root dry weight. Specific experimental procedures are listed subsequently. Experiment 1: Water Use of Quercus rubra, Q. shumardii, and Q. velutina Seedlings Under Outdoor Conditions Quercus rubra, Q. shumardii, and Q. velutina seedlings were transplanted to 15 cm diameter (6 in), 15 cm (6 in) deep (2.8 L [0.73 gal] No. 1 nursery containers; Nursery Supplies, Fair- less Hills, PA) containers and grown under greenhouse con- ditions described previously until 15 May. They were then moved out doors under 80% shade cloth for 2 weeks. The seedlings were transplanted to 11.4 L ([2.96 gal] No. 3 nurs- ery containers, 1200 Classic; Nursery Supplies) using a 3: 0.5:0.5:1 (pine bark:Comtil [composted municipal sewage sludge from the City of Columbus, OH:peat moss:quartz sand [by vol]) substrate supplemented with 3.6 kg (7.92 lb) dolo- mite, 1.2 kg (2.64 lb) gypsum, and 1.8 kg (3.96 lb) phospho- rus m−3. The seedlings were placed on 45 cm (18 in) centers in full sun and initially irrigated daily with 1.9 L (0.49 gal) water and fertilized weekly with 1.9 L (0.49 gal) of 250 mg NL−1 water-soluble fertilizer (20 to 20 to 20 Perters fertilizer; Scotts MiracleGro). Irrigation was delivered by 1.9 L (0.49 ©2006 International Society of Arboriculture gal) hr–1 emitters (NetafimTM; Shemin Nurseries, Inc., Addi- son, IL). The container surfaces were covered with fiber disks to minimize evaporation. In late June, irrigation was con- trolled by a plant-driven automated irrigation system (Gonza- lez and Struve 1992) and the monthly water use calculated as the product of the time the irrigation solenoid was “on” and the trickle irrigation emitter rate. In late August, ten plants per species were harvested. Plant growth, morphology, and irri- gation volume data were used to calculate water use seed- ling−1, cm height–1, cm−2 leaf area, and cm−2 root surface area. The data were subjected to one-way analysis of variance using a fixed-effects model with ten individual plant replica- tions per species. Experiment 2: Water Use of Q. macrocarpa, Q. palustris, and Q. prinus Under Greenhouse Conditions Q. macrocarpa, Q. palustris, and Q. prinus seedlings were produced under greenhouse conditions as described previ- ously in 12.5 cm (5 in) square × 15 cm (6 in) deep containers (250 XL Classic; Nursery Supplies). The seedlings were fer- tilized weekly with 100 mg N L−1. The seedlings were grown in a single greenhouse compartment in a completely random design using single plant replications. The numbers of seed- lings per species were 107, 253, and 66 for Q. macrocarpa, Q. palustris, and Q. prinus, respectively. When the seedlings reached QMI growth phase, they were watered to saturation, allowed to drain for 1 hr, and weighed with an electronic balance (TR-12001; Denver Instrument Co.). The seedlings were reweighed 24 hr later. After the water use trial, 25 seedlings from each species were randomly selected and de- structively harvested for dry weight, root and leaf area mea- surements. Similar water use statistics were calculated like in experiment 1. Additionally, for the harvested plants, the data were subjected to principal component analysis using 11 vari- ables: height, leaf and root area, shoot, root, total plant and shoot-to-root dry weight, and four measures of water use (water use seedling−1, water use cm−1 height, water use cm−2 leaf, and root areas). Data were subjected to analysis of vari- ance using single plant replications a fixed-effects model. Means were separated using Student-Neuman-Kuels test at P 0.05 level of significance. Experiment 3: Water Use of Quercus macrocarpa and Q. prinus Under Greenhouse Conditions Quercus macrocarpa and Q. prinus seedlings were grown in a single greenhouse compartment under conditions described previously. In this study, 2.8 L (No.1 round nursery contain- ers, 16.5 cm diameter × 17.8 cm deep [6.6 × 7.1 in]; Lerio Corp., El Campo, TX) containers filled with Metro Mix 360 substrate were used. Seedlings were hand watered to avoid moisture stress and fertilized weekly after the seedlings
September 2006
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