50 Zimmerman and Jull: Sodium Chloride Injury on Buds severe inner tissue discoloration occurred (Figure 4A). Inner tissue injury for Norway maple buds remained low for all NaCl treatments; they had significantly less inner tissue dis- coloration than littleleaf linden and wayfaringtree viburnum buds at 16,000 mg/L (16,000 ppm) NaCl, and wayfaringtree viburnum buds at 32,000 mg/L (32,000 ppm) NaCl. Severe outer tissue discoloration was detected only in wayfaringtree viburnum buds at 32,000 mg/L (32,000 ppm) NaCl (Figure 4B). Severe outer tissue discoloration in wayfaringtree vibur- num buds is probable at greater NaCl concentrations, al- though it was not detected at 64,000 mg/L (64,000 ppm) NaCl. Patterns of tissue discoloration reflected the unique bud morphology of each species. The numerous, tightly arranged waxy bud scales of Norway maple may have inhibited NaCl penetration to inner bud tissues, whereas the tomentose sur- face of naked wayfaringtree viburnum buds offered little pro- tection. Lumis et al. (1973) similarly reported that naked buds of glossy buckthorn (Rhamnus frangula L.) were more in- jured by salt spray than common buckthorn (Rhamnus ca- tharticus L.), a scaled species. In addition to the presence of bud scales, the number and arrangement of bud scales may be a factor in the salt tolerance of buds. Littleleaf linden buds have slightly fewer bud scales than Norway maple buds, pos- sibly accounting for the occurrence of moderate inner tissue injury. A bud’s ability to preclude salt from penetrating and accumulating in sensitive tissues relates to the bud’s salt tol- erance (Dirr 1976; Sinclair et al. 1987). January Collection Detection of severe inner and outer tissue discoloration indi- cated that buds from all species became more susceptible to NaCl injury in January. The interaction between species and NaCl was not significant for inner tissue discoloration (Table 1). All species exhibited a similar pattern of inner tissue injury in response to NaCl; the pattern plateaued at 1,000 mg/L (1,000 ppm) NaCl (data not shown). The differences in the severity of inner tissue discoloration among species were evident (P 0.0001) (Tables 1 and 3), indicating a relation Table 3. Effect of species on inner tissue discoloration of buds collected in January 2002 combined over nine NaCl concentrations. Species Acer platanoides Tilia cordata Viburnum lantana Inner tissue discoloration ratingz,x,y 2.9 a 3.6 b 4.2 c zRepresents the mean of 54 buds. xRating scale: 1 to 5 [1green/yellow tissue, 2detection of light-colored brown tissue (<10%), 3light-colored brown tissue (>10%), 4medium- brown tissue (100%), 5 dark-brown to black tissue (100%)]. yMean separation within column by pairwise t-tests, P 0.05. ©2006 International Society of Arboriculture Figure 5. Effect of NaCl and species on outer tissue dis- coloration of buds collected in January 2002. Standard error of the treatment mean difference was 0.50. Obser- vations 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%)]. In- ner tissue discoloration was nonsignificant. between bud morphology and inner tissue injury. Wayfaring- tree viburnum, which has naked buds, displayed severe inner tissue discoloration, whereas littleleaf linden had moderate discoloration and Norway maple had low inner tissue discol- oration. Both littleleaf linden and Norway maple have mul- tiple bud scales; however, the inner bud scales of Norway maple are sticky and contain milky sap, perhaps precluding salt from entering into primordial tissue. The interaction between species and NaCl was significant for outer tissue discoloration (P0.01) for January-collected buds (Table 1 and Figure 5). Species rankings for outer tissue injury differed from those of inner tissue injury. Although Norway maple buds had low to moderate inner tissue discol- oration, severe outer tissue discoloration occurred at all NaCl treatments. Outer bud tissues of wayfaringtree viburnum were also sensitive to NaCl: moderate injury occurred at 500 mg/L (500 ppm) NaCl and severe injury occurred at a con- centration as low as 1,000 mg/L (1,000 ppm) NaCl. Littleleaf linden buds had the lowest outer tissue discoloration of the three species, exhibiting moderate injury at 2,000 mg/L (2,000 ppm) NaCl and severe injury at 16,000 mg/L (16,000 ppm) NaCl. Bud scale surfaces of littleleaf linden have a glossy sheen, indicating the presence of protective cuticular wax. Although there is little research about the relation be- tween cuticular wax and salt spray tolerance of buds, research on needles from numerous species of pine (Pinus spp. L.) and spruce (Picea spp. A. Dietr.) has reported surface wax to be an effective barrier to salt spray (Townsend and Kwolek 1987; Dobson 1991).
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