Arboriculture & Urban Forestry 32(5): September 2006 205 reached QMI Lag-1 stage with the same fertilizer used in experiment 2 at 100 mg N L−1. Fertilization was stopped when the water use experiment was begun. For insect control, one 16 g (0.56 oz) application of imidacloprid (Merit; Bayer Corp., Kansas City, MO) per container was surface applied at QMI Lag-1. Experimental details are described in Drunasky and Struve (2005). When seedlings from both species reached either Lag-2 or Lag-3 QMI (the second or third flushes), 20 individuals were randomly selected and placed on 45.7 cm (18.28 in) centers in completely random design. The water use trial was con- ducted as before, but instead of one 24 hr water use period, two consecutive 48 hr water use periods were used. After the water use trial, seedlings were destructively harvested and height, leaf area, and leaf, root, shoot, plant dry weights, and shoot/root ratios were determined. The same water use statistics, principal component analysis (PCA), and mean separation tests were calculated and analyzed like in experi- ment 2. Experiment 4: Water Use of Quercus macrocarpa, Q. palustris, and Q. rubra Seedlings Under Greenhouse Conditions Acorns were collected from two Quercus macrocarpa, three Q. palustris, and 11 Q. rubra trees in central Ohio. Mother tree identity was maintained throughout the study. Acorns were cold stratified, germinated, transplanted, and grown to QMI Lag-2 or 3 as described in experiment 2. Between 47 and 98 seedlings from each mother tree were raised. Because of the large number of seedlings, three greenhouse compart- ments (with similar environmental conditions) were used. Two half-sib Q. rubra families were common to all three compartments; however, some half-sib Q. rubra families were grown in only one compartment. For the common Q. rubra families, each compartment was treated as a block with individual seedlings from the half-sib families placed within a compartment in a completely random design. A model A ET gauge (Ben Meadows Co., Janesville, WI) was placed in each compartment and read at the beginning and end of each water use measurement period. All seedlings within a com- partment were weighed on the same day, but seedlings from different compartments were weighed on a staggered sched- ule. Water use for individual seedlings was standardized by expressing water use statistics as g water loss cm−1 ET. Water use was measured over one 48 hr period and average daily water use per seedling calculated. At the end of the water use period, plant height was measured, but no destructive har- vests were done because seedlings with apparently efficient and inefficient water use characteristics were used as stock plants in asexual propagation studies. Water use seedling−1 and cm−1 height were calculated for all half-sib families. Data were subject to analysis of variance using a fixed-effects model. RESULTS Experiment 1 Quercus shumardii and Q. rubra seedlings were significantly taller, had greater root length and shoot, root, and total plant dry weights, but lower shoot-to-root ratio than Q. velutina seedlings. Additionally, Q. shumardii seedlings had greater leaf and root area than Q. velutina seedlings (Table 1). Quer- cus shumardii seedlings used the most water seedling−1; Q. velutina seedlings used the least (Table 2). However, water use cm−1 of height, water use cm−2 leaf or root surface area was greatest in Q. velutina seedling, whereas Q. shumardii seedling used the least (Table 2). Growth and water use data were not subjected to PCA as a result of low sample size (n 10 individuals per species). Experiment 2 At QMI Lag-2 (the period of time between the second and third growth flushes), Q. macrocarpa seedling were taller than Q. palustris and Q. prinus seedlings (Table 1). Quercus Table 1. Height, morphology, and dry weights of six oak species in experiments 1, 2, and 3. Surface area (cm2 Leaf Experiment no. 1 2 3 Species Q. rubra Q. shumardii Q. velutina Q. macrocarpa Q. palustris Q. prinus Q. macrocarpa Q. prinus n QMIz Height (cm) 10 3 to 4 50.6 by ) Root Root length (cm) 10 3 to 4 63.1 b 1596.8 b 648.0 b 5436.2 b 10 2 to 3 29.6 a 25 2 25 2 25 2 31.0 b 634.9 c 168.2 c 1265.2 b 21.1 a 19.3 a 83.2 a 661.4 a 20 3 to 4 43.9 a 1414.4 a 138.0 b 1271.7 b 20 3 to 4 81.9 b 1882.5 b 71.2 a 463.1 b 102.7 b 692.4 a 169.4 a 1190.7 ab 457.1 ab 5001.3 b 737.8 a 328.6 a 3014.3 a 203.2 a Dry weight (g) Shoot Root Total Shoot to root ratio 24.9 b 25.0 b 49.0 b 1.0 a 22.4 b 17.6 b 40.0 b 1.3 a 8.2 a 4.8 a 13.0 a 1.7 b 7.3 b 7.7 b 15.0 c 1.1 a 2.4 a 2.2 a 4.6 a 1.1 a 3.8 a 2.7 a 6.5 b 1.4 b 16.5 a 31.0 b 47.5 b 0.5 a 21.5 b 9.5 a 31.0 a 2.3 b zQuercus morphologic index are for the lag-phase (Hanson et al. 1986). yMeans within an experiment and column followed by different letters are significantly different from each other using the Student-Neuman-Kels test at the 0.05 level of significance. ©2006 International Society of Arboriculture
September 2006
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