244 Table 1. Shoot extension (cm), Net Photosynthesis (A. µmol m-2 Ferrini et al.: Withholding Irrigation During Establishment Phase s-1 ), Transpiration (E. mmol m-2 WUE Shoot extension (cm) 2006 T. platyphyllos T. cordata T. × europaea T. tomentosa P Irrigated Nonirrigated P P 30.2 66.4 35.9 29.9 ** 43.1 38.2 * ** 2007 45.4b 50.2b 58.6a 42.9b ** 53.4 43.1 ** N.S. (µmol m-2 2006 A s-1 4.6d 9.8a 5.9c 8.2b ** 7.3 6.6 * N.S. ) 2007 8.1b 10.3a 10.5a 10.3a ** 10.1 9.5 N.S. N.S. E (mmol m-2 2006 Species 1.9 3.2 2.4 3.0 ** Irrigation 2.7 2.4 ** s-1 ) 2007 2.8 3.4 3.4 3.4 ** 3.4 3.1 ** Species × Irrigation ** * T. tomentosa had lower E than T. cordata when irrigation was withheld, but E did not differ between the two species in well- watered conditions. T. platyphyllos and T. × europaea had lower E than the former two cultivars when irrigation was withheld. Irrigation increased E in T. × europaea but not in T. platyphyl- los. In 2007, T. cordata had higher E than T. platyphyllos in non irrigated conditions. In the presence of irrigation, T. tomentosa 2006 2.4c 3.1a 2.5c 2.8b ** 2.7 2.8 N.S. N.S. s-1 ), Water Use Efficiency (WUE) and leaf greenness index (Chl, Unit SPAD) in Tilia spp grown under different irrigation regimes. Data are reported as annual means (five sampling dates in 2006, five in 2007), and subjected to two-way ANOVA. (µmol CO2 /mmol H2 Chl O) 2007 2.9 3.0 3.1 3.0 N.S. 3.0 3.1 N.S. N.S. (Unit SPAD) 2006 38.6d 49.1a 43.4c 46.9b ** 44.0 45.0 N.S. N.S. Different letters within the same column indicate statistically differences among species at P < 0.05 (*) or P < 0.01 (**) using Duncan’s MRT. showed higher E than T. × europaea. Among the species stud- ied, the lowest E was measured in T. platyphyllos (Figure 2). In 2006, Acer platanoides ‘Deborah’ had higher shoot exten- sion, mean annual A, and leaf chlorophyll content than the other two cultivars (Table 2). No differences were found for WUE and stem diameter (data not shown). In 2007, cultivar ‘Deborah’ dem- onstrated faster growth than the other cultivars. There were no differences in A and chlorophyll content among the cultivars in 2007. Irrigation had no effect on shoot extension, trunk diameter growth (data not shown) and chlorophyll content in 2006 (Table 2), but increased mean annual A and E and decreased WUE. In 2007, irrigation reduced shoot growth. In 2007, mean annual A was unaffected by irrigation and mean annual E was increased. In spite of this, no difference in WUE was found between irri- gated and nonirrigated plants. Significant interaction between factors was found for E in 2006 and 2007. In 2006, nonirrigated ‘Deborah’ maple had higher E than nonirrigated ‘Emerald Queen’ which, in turn, had higher E than nonirrigated ‘Summershade. Where irrigation was applied, ‘Deborah’ had higher E than the other two cultivars (Figure 3). In 2007, nonirrigated ‘Debo- rah’ had higher E than the other two cultivars. In the presence of irrigation, differences among cultivars disappeared in 2007. Figure 3. Means separation of those parameters [transpiration (E, mmol s-1 m-2 unaffected by water shortage (Table 3). Contrary to the other spe- cies, nonirrigated T. platyphyllos had higher F0 value was used to quantify the detrimental effects of drought on leaf tissues. In T. cordata, T. × europaea and T. tomentosa, F0 on July 12, 2007 if ) in 2006 and 2007], which were significantly affected by cultivar × irrigation interaction in Acer platanoides. In this case, Duncan’s Multiple Range Test was used to compare the cultivars for each level of irrigation separately. ©2009 International Society of Arboriculture compared to irrigated plants. Increases in F0 have been reported in Olea, Quercus, and some Acer and Fraxinus genotypes in response to water and other environmental and chemical stresses (Angelop- ulos et al. 1996; Percival et al. 2003; Percival 2005; Percival et al. Species/Cultivar Strategies to Cope with Water Stress Drought tolerance of the different species was evaluated comparing chlorophyll fluorescence of different individu- als of the same species/cultivar grown in well-watered or water-shortage conditions (Angelopulos et al. 1996; Li et al. 2006). Chlorophyll content was not affected by drought treatment in linden species in 2006 and 2007 (Table 3). F0 is the minimal fluorescence of dark-adapted leaves and this was 2007 43.5c 50.8b 51.9b 55a ** 50.3 50.3 N.S. N.S.
September 2009
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