Journal of Arboriculture 31(2): March 2005 69 three concentrations, with the following exceptions. In the 1999 trial, sucrose and glucose at 25 g/L (3.4 oz/gal) (root dry weight); glucose at 50 g/L (6.8 oz/gal) (root growth potential); and maltose at 25 g/L (3.4 oz/gal) (root growth potential, root dry weight) and at 70 g/L (10.3 oz/gal) (root dry weight), where no significant effects occurred. In the 2003 trial, sucrose and fructose at 25 g/L (3.4 oz/gal) (root growth potential); fructose at 70 g/L (10.3 oz/gal) (root growth potential); sucrose at 25 g/L (3.4 oz/gal); and glucose at 70 g/L (10.3 oz/gal) (root dry weight), where no significant effects were recorded. By week 24 (1999 trial), a significant increase (P < 0.05) in growth was recorded, with the exceptions of glucose and fructose at 25 g/L (3.4 oz/gal) (root dry weight); glucose at 50 g/L (6.8 oz/gal) (root length); sucrose, fructose, glucose, and maltose at 25 g/L (3.4 oz/gal) (root growth potential); sucrose, fructose, and glucose at 25 g/L (3.4 oz/gal); maltose at 25, 50, and 70 g/L (3.4, 6.8, and 10.3 oz/gal) (girth, shoot dry weight); and fructose and glucose at 25 g/L (3.4 oz/gal) (leaf dry weight), where values were not significantly higher than controls. At week 24 in the 2003 trial, a significant increase (P < 0.05) in growth was recorded, with the exceptions of sucrose and fructose at 25 and 70 g/L (3.4 and 10.3 oz/gal) (root dry weight); sucrose, fructose, and glucose at 50 g/L (6.8 oz/gal), glucose at 25 g/L (3.4 oz/gal), and fructose at 70 g/L (10.3 oz) (root length); sucrose and fructose at 25 and 70 g/L (3.4 and 10.3 oz/gal), and glucose at 70 g/L (10.3 oz/gal) (root growth potential); sucrose and glucose at 25 g/ L (3.4 oz/gal), and fructose and glucose at 50 and 70 g/L (6.8 and 10.3 oz/gal) (girth); sucrose, fructose, and glucose at 25 g/L (3.4 oz/gal), glucose at 50 and 70 g/L (6.8 and 10.3 oz/gal) (shoot dry weight); and sucrose, fructose, and glucose at 25 g/L (3.4 oz/gal) (leaf dry weight), where values were higher, but not significantly more so than controls. In both 1999 and 2003 trials, the highest increases in girth and in root, shoot, and leaf dry weight at the cessation of the experiment were recorded following applications of sucrose as a root drench at a concentration of 70 g/L (10.3 oz/gal). Application of the sugars tested in this investigation to root systems of birch following severe root pruning reduced mortality from 15% (controls) to zero in the 1999 trial and 5% to zero in the 2003 trial. DISCUSSION Results of this investigation show that application of the sugars sucrose, fructose, and glucose as a root drench improved root growth of young, newly transplanted birch following severe root pruning. Likewise, reduced mortality and increased shoot and leaf dry weight and girth in treated trees recorded at the cessation of both the 1999 and 2003 field trials indicate applications of sugars would aid in the survival of young birch trees following transplanting. Further research is required to determine whether applying sugars to root systems of other tree species would induce similar beneficial responses. Improved root vigor, as assessed by higher root growth potential values at week 6, in trees supplemented with sucrose, fructose, and glucose in both trials and maltose in the 1999 trial and reduced photosynthetic rates recorded at the same time indicate that these sugars were used as direct substrates for root growth (Lindqvist and Asp 2002). Sucrose is the major photoassimilate transported from source to sink tissues in birch that is hydrolyzed into glucose and fructose to provide energy via respiration, while maltose is the predominant sugar in barley (Salisbury and Ross; 1985; Lindqvist and Asp 2002). Rapid uptake, transfer, and breakdown mechanisms that naturally exist within plants for utilizing these four sugars may account for the stimulatory root growth responses recorded by week 6. Sugars such as galactose and rhamnose are not directly used as substrates for growth but have been shown to play important roles in plant defense systems (Percival et al. 1998). This may account for their failure to induce any alterations in growth and leaf photosynthetic properties recorded in this investigation. No significant effects on growth of birch were recorded following application of the sugar maltose in the 2003 trial. Contrary to this finding, significant increases in growth were recorded in the 1999 trial. Such a response is disadvanta- geous to professionals involved in urban tree care where products with repeatability and reliability are required. Although not explored, alterations in gene expression may explain the growth and leaf photosynthetic responses recorded at the whole plant level. Reduced photosynthetic rates, chlorophyll fluorescence, and leaf chlorophyll and carotenoid concentrations, coupled with increased root growth potential and root dry weight recorded at week 6, would indicate repression of photosynthetic genes and upregulation of genes involved in root vigor in the short term (Koch 1996; Martin et al. 1997). By week 24, the genetic balance is restored as reflected by no significant difference in leaf chlorophyll fluorescence, photosynthetic rates, and leaf chlorophyll and carotenoid content between treated and control trees. Alternately, biologically active organic molecules such as sugars, sea weed extracts, and betaines, when applied to soils, have been shown to induce changes in the naturally occurring soil rhizosphere popula- tions—resulting in alterations to plant nutrient uptake patterns (Pattison 1994; Walsh 1997). Such changes may also have contributed to improved growth and reduced mortality recorded in this investigation (Blunden and Woods 1969; Finnie and van Staden 1985). Rapid root regeneration is associated with successful transplant establishment. Significant increases in the root growth potential recorded by week 6 indicate short-term ©2005 International Society of Arboriculture
March 2005
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