Arboriculture & Urban Forestry 35(3): May 2009 tively) root dry weights (g). Leaf area and number were estimated by scanning a subsample of the leaves (Mustek Scan Express A3 USB) and with image analysis software (Image Tool, U. of Texas Health Services Center, San Antonio, TX), also using the propor- tion of the subsample weight-to-total leaf weight to estimate total leaf number and area. From this data, the following variables were calculated: total shoot dry weight (leaves + shoot dry weights), to- tal root dry weight (fine + coarse root dry weight), total plant dry weight (total shoot + total root dry weight), percent of total plant dry weight in leaves, roots, stems, fine and coarse roots, shoot- to-root dry weight ratio (total shoot dry weight/total root dry weight), water transpiring-to-absorbing ratio [leaf surface area/ fine root dry weight (cm2 g-1 )], specific leaf weight (cm2 g-1 average height adjusted water use (g cm-2 seedling height day-1 Data were subject to multivariate analysis of variance using the ) and ). general linear model procedure (SPSS, Version 12.0) as a fixed effects model with two replications with 20 seedlings per replica- tion and seed source. Means were separated using the Student- Neuman-Kuels test at the α ≤ 0.05 level of significance. The data were also subjected to principal component analysis (SPSS, Ver- sion 12.0) by seed source using the 20 variables described above. RESULTS AND DISCUSSION Substrate bulk density averaged 0.43 g cm-3 (Table 2). The sub- strate had 63.7% total pore space and 46.8% water-filled pore space at field capacity (Table 2). The 2.1 L substrate volume contained an estimated 0.98±0.04 L (0.25 gal ±0.01) of wa- ter. Maximum water loss in any one day during the three day trial was < 0.145 L (0.04 gal), thus, the plants were not under substrate moisture stress during the three day water use peri- od. Average PAR between sunrise and sunset ranged from 160 to 180 µmoles m-2 s-1 ; daily average relative humidity ranged from 47% to 51% and average daily temperature ranged from 19 to 21°C (67 to 70°F). The greenhouse was cooled by con- vection through a combination of side wall and roof vents. Table 2. Physical properties of the 3:1 peatmoss:pumice (by vol) substrate in 18 cm tall, 2.1 L volume container. Variable Bulk density (g cm-3 Total pore space (%) Water-filled pore space Air-filled pore space ) z Each value is the mean of five containers. Water Use Seedlings of Quercus robur were the tallest and had the great- est water use per seedling, but had lower height-adjusted water use than Q. cerris sources (Table 3). However, water use per cm2 each species, there were differences between the sources in seed- ling height, water use per cm2 leaf surface was lower than Q. pubescens sources. Within leaf area and height-adjusted wa- ter use, except between the Q. robur sources for water use per seedling and between the Q. cerris sources for height-adjusted water use (Table 4). Among all the sources, water use per seed- ling varied by almost 200% (Q. cerris Amiata and Q. pubescens Cerreta sources versus both Q. robur sources, 36.0 and 32.6 g versus 72.1 and 74.7 g seedling-1 day-1 The Q. robur Cascine source had lower water use per cm2 , respectively) (Table 4). leaf Figure 1. The relationship among seed sources, two sources from each of three Quercus species (cerris, pubescens, and robur). Total shoot length, total plant dry weights and leaf area-to-fine root dry weight were plotted against the first, second and third (respectively) principal component axes. The numbers in paren- thesis refer to the seed source numbers in Table 1. ©2009 International Society of Arboriculture Mean 0.43z 63.7 46.8 16.5 Standard deviation 0.05 2.3 2.0 4.2 115 area than the Pineta source, which was higher than the Q. cer- ris Sellano source, and similar to the Amiata source, and lower than both Q. pubescens sources (Table 4). Height-adjusted wa- ter use varied by 80% among all the sources [Q. robur Cascine versus Q. pubescens Cerreta (1.2 versus 1.5 g cm-2 height day- 1 )]. Thus, the basis for the differences in water use among the sources was complex. Some of the differences in water use per seedling can be attributed to differences in seedling size; larger seedlings, relative to shorter seedlings, tended to have greater leaf area and greater water use per seedling (Figure 1). However, the correlations between seedling height and water use per seedling were low; R2 values for individual sources were < 0.05, except for the Q. pubescens Cerreta source where it was 0.21. Also, there were low correlations between water use per seedling and height- adjusted water use (Figure 2). The relationship between height- adjusted water use and seedling height of the six seed sources used in this study was markedly different from that of six Eastern North American Quercus species. For the Eastern North Ameri- can species, when the individual seedling heights within a 1/2-sib family were plotted against height-adjusted water use, a graph similar to an exponential decay curve was seen (Struve et al. 2006). No such pattern was seen within the Italian seed sources. As a summary example, the seedlings in the tallest source, Q. robur Cascine, used the highest water seedling-1, but had the lowest water use per cm2 leaf area and the lowest height-adjust- ed water use. In contrast, the seedlings in the shortest source, Q. pubescens Cerreta, used the least water per seedling, but had the greatest water use per cm2 leaf area and the highest height- adjusted water use. Further, Figures 1 and 2 reveal significant within source variation in water use characteristics. Thus, bas- ing a species’ water use characteristics on a single water use pa- rameter or on a single seed source can be misleading. The great variation in water use characteristics between species, sources and within sources presents an opportunity for genetic improve-
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