Arboriculture & Urban Forestry 32(2): March 2006 45 Sodium Chloride Injury on Buds of Acer platanoides, Tilia cordata, and Viburnum lantana E.M. Zimmerman and L.G. Jull Abstract. Dormant lateral buds of Norway maple (Acer platanoides L.), littleleaf linden (Tilia cordata Mill.), and wayfaringtree viburnum (Viburnum lantana L.) were collected and exposed to nine NaCl concentrations: 0, 500, 1,000, 2,000, 4,000, 8,000, 16,000, 32,000, and 64,000 mg/L (0, 500, 1,000, 2,000, 4,000, 8,000, 16,000, 32,000, and 64,000 ppm) in December 2001 and January and March 2002. Electrolyte leakage and visual observations of inner and outer tissue discoloration were used to assess injury. Bud injury generally increased as NaCl concentration increased. Bud morphologies of each species were related to tissue discoloration patterns; naked buds were more susceptible to NaCl than those with bud scales. Buds also exhibited seasonal NaCl resistance; the greatest resistance occurred in December. Norway maple, wayfaringtree viburnum, and littleleaf linden buds experienced 50% electrolyte leakage at calculated NaCl values of 12,941, 16,901, and 42,594 mg/L (12,941, 16,901, and 42,594 ppm) NaCl, respectively, but no severe inner tissue discoloration occurred at any level of NaCl treatment. In January, 50% electrolyte leakage occurred at lower NaCl concentrations in Norway maple [7,165 mg/L (7,165 ppm)] and littleleaf linden buds [27,118 mg/L (27,118 ppm)]. Moderate to severe inner tissue injury was detected for all species at 1,000 mg/L (1,000 ppm) NaCl. Buds were most susceptible to NaCl injury in March, with moderate to severe inner tissue discoloration occurring in wayfaringtree viburnum and littleleaf linden buds at 500 mg/L (500 ppm) NaCl. Key Words. Bud morphology; electrolyte leakage; salt tolerance; tissue discoloration; winter injury. Winter roads and walkways must be maintained ice-free to provide safe mobility for pedestrians and motorists. De-icing salts are used extensively to melt ice and snow and are then dispersed from road surfaces by plowing, runoff, and aerosol spray generated by traffic and wind, causing significant dam- age to plants (Hootman and Kelsey 1992). Sodium chloride (NaCl) is the most commonly used de-icing salt because of its effectiveness, availability, and comparatively low cost. How- ever, the deleterious effects of NaCl to roadside trees and shrubs are well documented (Lumis et al. 1973; Hofstra et al. 1979; Dobson 1991). Plants are injured by NaCl either by root uptake or deposition onto plant surfaces causing osmotic stress and toxicity to tissues. Elevated soil salinity is gener- ally localized to areas bordering salted roadways (Hootman et al. 1994), whereas salt spray travels greater distances. Hoot- man and Kelsey (1992) found that salt spray increased Na levels in needles of eastern white pine (Pinus strobus L.) up to 1,018 m (3,340 ft) from tollways and detected visible salt spray damage at 378 m (1,240 ft). Hofstra et al. (1979) simi- larly reported injurious Na and Cl accumulation in needles of white pine at distances of 100 m (330 ft) or more from road- ways but found no elevated levels of Na and Cl in the soil at distances greater than 30 m (99 ft) from pavement. Numerous studies have evaluated species for salt spray tolerance (Moxley and Davidson 1973; Lumis et al. 1975; Townsend and Kwolek 1987). However, salt spray concen- trations in roadside observation studies were not quantified, and the salt concentrations used for species evaluations have varied. There is little information about the occurrence and severity of injury at different salt concentrations. Landscape plants are exposed to a wide range of salt concentrations, which vary by location, method and amount of salt applica- tion, and type of storm (Herrick 1988; Buttle and Labadia 1999). More knowledge on the relation between injury and varying salt concentrations is needed. Salt injury has been correlated with the accumulation of Na+ and Cl− ions in plant tissues (Hofstra and Lumis 1975; Sucoff et al. 1976). The symptoms of salt spray are delayed budbreak, reduced leaf size, marginal leaf scorch, witches’ broom (tufted growth), and crown dieback in deciduous spe- cies (Lumis et al. 1975; Sinclair et al. 1987; Dobson 1991; Appleton et al. 1999). Salt spray enters deciduous species through nonlignified bud tissues, bud and leaf scars, and young shoots (Dobson 1991). Salt tolerance of many species appears to be related to their ability to preclude salt from entering and accumulating in sensitive tissues (Dirr 1976; Sinclair et al. 1987). Morphological factors such as bud size and the nature of scales affect salt uptake (Hofstra et al. 1979). Plants with resinous buds such as eastern cottonwood (Populus deltoides Bartr. ex Marshall) and common horsechestnut (Aesculus hippocastanum L.) or buds sub- merged in twigs of black locust (Robinia pseudoacacia L.) ©2006 International Society of Arboriculture
March 2006
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