Arboriculture & Urban Forestry 37(6): November 2011 281 treated trees, respectively), but otherwise had no effect on total phenolics or tan- nin concentrations in 2003 or 2004. Fo- liar concentrations of total phenolics and condensed tannins of Austrian pine were not affected by paclobutrazol (Table 3). Fertilization or the interaction between fertilization and the regulator had no ef- fect on foliar tannin and phenolic con- centrations of paper birch and Austrian pine (Table 3). Total foliar terpene con- centrations of Austrian pine foliage were also not affected by paclobutrazol, fer- tilization, or their interaction (Table 3). Trunk growth of paper birch was in- versely correlated with foliar tannins and phenolic concentrations in 2003 and in 2004 (Figure 4); however, there was no sig- nificant correlation between trunk growth of Austrian pine and foliar concentra- tions of tannins, phenolics, or terpenes. Figure 1. Effects of paclobutrazol on growth of paper birch and Austrian pine. Data are presented as least squares means ± 1 SE. Exact statistical significance (*) is reported in Table 1. Figure 2. Effects of paclobutrazol on photosynthesis of paper birch and Austrian pine. Data are presented as least squares means ± 1 SE. Exact statistical significance (*) is reported in Table 2. trees, respectively), and on August 24, 2004 (2.19 ± 0.1% versus 1.87 ± 0.1%, for fertilized and non-fertilized trees, respectively) (Table 3). Fertilization had no effect on nitrogen concentration of one-year-old foliage of Austrian pine on May 6, 2004 (1.55 ± 0.1% versus 1.39 ± 0.1%, for fertilized and non-fertilized trees, re- spectively), or on May 10, 2005 (1.25 ± 0.1% versus 1.24 ± 0.1%, for fertilized and non-fertilized trees, respectively) (Table 3). Secondary Metabolism Paclobutrazol increased foliar condensed tannin concentrations of paper birch by 35% on June 24, 2003 (Table 3; 21.5 ± 1.5% versus 15.9 ± 1.5% for paclobutrazol-treated fertilized and non- Insect Performance In 2003, paclobutrazol did not affect re- sistance of paper birch to gypsy moth or forest tent caterpillar, as evidenced by no difference in larval growth (Table 4; Fig- ure 5) or survival (data not shown). How- ever, paclobutrazol increased resistance of paper birch to both gypsy moth and white- marked tussock moth in 2004, as evidenced by decreased growth of larvae on treated trees (Table 4; Figure 5). However, larval survival was not affected. Paclobutrazol had no effect on growth or survival of European pine sawfly larvae on Austrian pine in either year (Table 4; Figure 5). Fertilization had no effect on gyp- sy moth survival but increased larval growth by 30% in 2004 (38.3 ± 3.4 mg versus 29.7 ± 2.7 mg on fertilized and non-fertilized trees, respectively). Fer- tilization had no effect on gypsy moth growth and survival in 2003, nor did it have any effect on the other insect spe- cies in either 2003 or 2004 (Table 4). Notable Physiological Responses Paclobutrazol induced premature leaf senescence (yellowing) of paper birch beginning in mid-August 2003, and abscission in early September, which occurred about one month prior to untreated trees. The effect was most prominent on older foliage in the interior of the canopy. No such response was observed in 2004 or in Austrian pine in any year. Paclobutra- zol dramatically stimulated female reproductive effort of paper birch in 2004 (207.3 versus 1.8 pistillate catkins/tree for paclobutrazol-treated and untreated trees, respectively). Although paper birch is a monecious species (Perala and Alm 1990), paclobutrazol had no effect on male (staminate) cat- ©2011 International Society of Arboriculture
November 2011
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