XYLEM VASCULAR ANATOMY AND WATER TRANSPORT OF SALICORNIA-EUROPAEA

The xylem anatomy, changes in vessel member diameter at stem nodes and branch junctions, and effects of these changes on water flow rates an d water potential in greenhouse and field grown Salicornia europaea L. (Chenopodiaceae) have been investigated. There was a two-fold decreas e in vessel diameter at branch junctions and stem nodes. In greenhouse grown plants, this decrease resulted in a 1000-fold decrease in water flow rates, and a four- to eight-fold increase in resistance to water flow across branch junctions and stem nodes relative to within-intern ode flow rates. However, in field grown plants, there were no differen ces in water flow across branch junctions and stem nodes compared with water flow within internodes. Water potentials in field plants were 3 -15 times lower than in greenhouse plants. Under field conditions, hyp ersalinity is probably the key determinant of Salicornia water relatio ns. Localized reductions in vessel member diameter in Salicornia appea r to result from developmental changes in vasculature attending axilla ry bud growth. Reductions in Salicornia vessel diameter, therefore, ma y not be hydraulically functional adaptations per se. Rather, they may reflect a consequence of developmental branching.