Arboriculture & Urban Forestry 32(2): March 2006 51 March Collection Buds from all species were most susceptible to NaCl injury in March because inner and outer tissue discoloration occurred at lower NaCl concentrations than in January (Figures 5 and 6). Species differences in inner tissue discoloration were sig- nificant in response to NaCl (P 0.0001; Table 1 and Figure 6A). Severe inner tissue discoloration occurred at 500 mg/L (500 ppm) NaCl in buds of wayfaringtree viburnum. Little- leaf linden buds showed moderate injury at the deionized water treatment and severe injury at 1,000 mg/L (1,000 ppm) NaCl. Possible freezing injury before collection in January and March in sampled buds may account for observations of severe injury at the deionized water treatment (Figure 1). Equivalent injury in Norway maple buds occurred at higher NaCl concentrations. Inner tissues of Norway maple buds exhibited moderate injury at 2,000 mg/L (2,000 ppm) NaCl and severe injury at 8,000 mg/L (8,000 ppm) NaCl. An un- explainable sudden drop in inner tissue discoloration in Nor- way maple buds occurred at 4,000 mg/L (4,000 ppm) NaCl. However, salt levels of 4,000 mg/L (4,000 ppm) NaCl are likely to be injurious, as moderate discoloration occurred at a lower NaCl concentration. The interaction between species and NaCl was also sig- nificant for outer tissue discoloration (P 0.0001) (Table 1 and Figure 6B). Wayfaringtree viburnum buds suffered se- vere outer tissue discoloration in response to all NaCl treat- ments. Equivalent injury occurred at higher NaCl concentra- tions in scaled buds. Norway maple and littleleaf linden buds showed moderate outer tissue injury at 500 mg/L (500 ppm) NaCl. Severe outer tissue injury occurred at 1,000 mg/L (1,000 ppm) NaCl in littleleaf linden buds and at 2,000 mg/L (2,000 ppm) NaCl in Norway maple buds. In addition to time of year (dormancy state) and NaCl concentration, NaCl injury depends on the type of evaluation method (i.e., visual tissue discoloration or electrolyte leak- age). Combining electrolyte leakage and visual observation tests provides a more detailed representation of NaCl injury than measuring only one variable. Electrolyte leakage tests provided estimations of total bud injury but did not account for the location of injury within buds (Calkins and Swanson 1990). Inner bud tissues contain leaf primordia and meriste- matic tissue that generate new stems, foliage, lateral buds, and reproductive structures (Taiz and Zeiger 1998). Thus, inner tissue injury could severely inhibit new growth in spring. Simini and Leone (1986) reported that budbreak in Norway maples was not affected by a salt spray concentration of 40,000 mg/L (40,000 ppm) Cl or 65,900 mg/L (65,900 ppm) NaCl. Although Norway maple buds suffered substan- tial electrolyte leakage at NaCl concentrations considerably lower than 65,900 mg/L (65,900 ppm) NaCl, visual observa- tions showed that the majority of injury occurred in bud scales and outer tissue. Higher inner tissue discoloration in buds of littleleaf linden and wayfaringtree viburnum may be an indication that their buds were less effective at precluding NaCl penetration. Inner tissue injury in these species may impede new growth in spring. CONCLUSIONS Figure 6. Effect of NaCl and species on inner (A) and outer (B) tissue discoloration of buds collected in March 2002. Standard error of the treatment mean difference was 0.52 for inner tissue discoloration and 0.42 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 tis- sue (>10%), 4 = medium-brown tissue (100%), 5 = dark- brown to black tissue (100%)]. Results of this experiment imply that buds with numerous bud scales have increased primordial tissue protection against salt spray with lower internal tissue discoloration. However, these results should be interpreted with caution. Bud mor- phology should be considered when testing species for salt tolerance, but a plant’s response to salt can be influenced by many factors, including genetic differences, type of exposure (soil salt or salt spray), exposure intensity, biotic or abiotic, and climatological/seasonal factors. The bud’s salt tolerance ©2006 International Society of Arboriculture
March 2006
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