Arboriculture & Urban Forestry 32(2): March 2006 49 Table 2. Concentrations of NaCl corresponding to 50% electrolyte leakage in dormant vegetative buds. Monthz December January Species Acer platanoides Tilia cordata Viburnum lantana Acer platanoides Tilia cordata Viburnum lantana NaCl (mg/L) ±SE 12,941x,y 42,594v 16,901 7,165 27,118 18,804 ±406w ±9,488 ±2,064 ±2,973 ±4,133 ±7,314 zMarch data are not shown (nonsignificant). xLog10 transformation of quadratic data were conducted in order to fit a linear model. yRepresents the mean of values obtained from six linear models. wCalculated as lower confidence interval subtracted from upper confidence interval, divided by two. vTwo observations were not used because electrolyte leakage did not reach 50%. occurred in the branch samples of all species within 2 weeks of collection, indicating the buds were under ecodormancy (Lang et al. 1987). No significant interaction between species and NaCl concentration occurred (Table 1). Average electro- lyte leakage ranged from 33% in buds treated with deionized water to 79% in buds treated with 64,000 mg/L (64,000 ppm) NaCl (data not shown). Main effects of NaCl and species were both significant (P 0.0001). Differences in bud elec- trolyte leakage between species were insignificant at concen- trations of less than 8,000 mg/L (8,000 ppm) NaCl, but spe- cies differences occurred at concentrations of 8,000 mg/L (8,000 ppm) NaCl and greater (data not shown). Wayfaring- tree viburnum buds had the highest average electrolyte leak- age (53.2%), followed by buds of Norway maple (47.3%) and littleleaf linden (31.1%) when averaged over all NaCl con- centrations. This is in contrast to the other two collection periods, when Norway maple buds exhibited the highest elec- trolyte leakage, followed by wayfaringtree viburnum and littleleaf linden buds, respectively. It appeared that increased physiological and morphological activity related to spring deacclimation decreased the buds’ NaCl resistance, espe- cially in wayfaringtree viburnum buds. Cold temperatures in March 2002 may have also contributed to injury in buds of all species, possibly accounting for the increased electrolyte leakage in control buds (Figure 1). Visual Discoloration Visual observations were conducted to determine whether electrolyte leakage was occurring from outer or inner bud tissue. Injury to inner bud tissue was considered more impor- tant than injury to scales and outer bud tissue because pri- mordial tissue was affected. Injured tissue turned brown to black after the 10 to 12 day incubation period. Bud tissues with a rating of 3 (light-colored browning >10% of area) were considered to be moderately injured, and bud tissues with a Figure 4. Effect of NaCl and species on inner (A) and outer (B) tissue discoloration of buds collected in Decem- ber 2001. Standard error of the treatment mean differ- ence was 0.37 for inner tissue discoloration and 0.45 for outer tissue discoloration. Observations were rated on a scale of 1 to 5 [1 = green/yellow tissue, 2 = detection of light-colored brown tissue (<10%), 3 = light-colored brown tissue (>10%), 4 = medium-brown tissue (100%), 5 = dark-brown to black tissue (100%)]. ©2006 International Society of Arboriculture rating of 4 (medium-brown tissue in 100% of area) or 5 (dark-brown to black tissue in 100% of area) were considered to be severely injured. In general, outer tissue discoloration was more severe than inner tissue discoloration. Fungal growth occurred on buds of all three species at the 64,000 mg/L (64,000 ppm) NaCl treatment but was inconsistent at lower NaCl concentrations (data not shown). Buds with se- vere tissue discoloration and/or fungal growth often had a water-soaked appearance. December Collection Interactions between species and NaCl concentration for in- ner (P 0.001) and outer (P 0.01) tissue discoloration were significant in December (Table 1 and Figure 4). Buds from all species exhibited some tolerance to NaCl because no
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