48 Zimmerman and Jull: Sodium Chloride Injury on Buds Figure 2. Determination of NaCl concentration corre- sponding to 50% electrolyte leakage for Acer plata- noides buds collected in December 2001. Equation for the NaCl response is Y = 39.5x − 111.7, where Y = elec- trolyte leakage (%) and x = Log10 of NaCl concentration. The interaction between species and NaCl concentration was significant in December (P0.001) (Table 1 and Figure 3A). Buds of Norway maple were the most susceptible to NaCl-induced electrolyte leakage, experiencing 50% electro- lyte leakage at 12,941 mg/L (12,941 ppm), followed by way- faringtree viburnum buds at 16,901 mg/L (16,901 ppm) and littleleaf linden buds at 42,594 mg/L (42,594 ppm) NaCl (Table 2). Buttle and Labadia (1999) reported 6,506 mg/L (6,506 ppm) Na and 9,916 mg/L (9,916 ppm) Cl [equivalent to 10,725 and 25,206 mg/L (10,725 and 25,206 ppm) NaCl, respectively] in snow sampled from highway medians. There- fore, concentrations of NaCl that induced 50% electrolyte leakage (severe injury) in buds of wayfaringtree viburnum and Norway maple were within the range of those found in roadside snow. Although no reports of NaCl concentrations more than 25,206 mg/L (25,206 ppm) were found, higher NaCl concentrations are probable in snow, slush, and melt- water found directly on road surfaces, especially in locations requiring high salt applications (i.e., intersections, bridges, and highway ramps). January Collection Daily maximum temperatures preceding the January collec- tion ranged from −5°C to 13°C (23°F to 55°F) (Figure 1). The buds were fully dormant; no budbreak occurred in any of the cut branch samples. Average electrolyte leakage ranged from 23% in buds treated with deionized water to 71% in buds treated with 64,000 mg/L (64,000 ppm) NaCl. The interaction between species and NaCl was significant for January- collected buds (P 0.01) (Table 1 and Figure 3B). Buds of Norway maple, littleleaf linden, and wayfaringtree viburnum again had a significant quadratic response to NaCl (P 0.0001). Species rankings for bud electrolyte leakage in re- ©2006 International Society of Arboriculture Figure 3. Effect of NaCl and species on electrolyte leakage of buds collected in December 2001 (A) and January 2002 (B). Standard error of the treatment mean difference was 2.81 for December 2001 and 5.18 for January 2002. sponse to NaCl were similar to those of December-collected buds, although 50% electrolyte leakage of littleleaf linden and Norway maple buds occurred at lower NaCl concentra- tions. Norway maple buds suffered 50% electrolyte leakage at 7,165 mg/L (7,165 ppm), followed by wayfaringtree viburnum at 18,804 mg/L (18,804 ppm) and littleleaf linden at 27,118 mg/L (27,118 ppm) NaCl (Table 2). The reason for the decreased NaCl tolerance in littleleaf linden and Norway maple buds is uncertain. It is possible that the endogenous seasonal rhythm for cold hardiness (Weiser 1970; Harrison et al. 1978) affected the salt tolerance of buds. Numerous woody species exhibit greatest resistance to cold injury be- tween mid-December and early January (Kang et al. 1997; McNamara et al. 2002). Slight midwinter changes in metabo- lism, tissue water content, or bud morphology (Ashworth and Wisniewski 1991; Rinne et al. 1994) may have occurred, although undetected, thus altering the buds’ NaCl tolerance. March Collection Maximum daily temperatures preceding the March collection ranged from −18°C to 13°C (0°F to 55°F) (Figure 1). Budbreak
March 2006
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