Comparative vessel anatomy of arctic deciduous and evergreen dicots

Arctic tundra plant species exhibit striking variation in leaf character an d growth form. Both are likely related to differences in vessel anatomy, an d all may affect responses to climate changes in the Arctic. To investigate the relationships among leaf character, growth form, vessel anatomy, and s usceptibility to freeze-thaw-induced xylem cavitation, xylem vessel charact eristics were compared among six deciduous and six evergreen arctic dicot s pecies of erect and prostrate growth forms. We hypothesized that deciduous and erect species would have larger and longer vessels than evergreen and c ushion/mat-forming species. Vessel lengths, diameters, and densities were m easured for each species. Theoretical vessel flow rates were calculated usi ng Poiseuille's law for ideal capillaries. Flow rates were used to determin e the susceptibility of vessels to cavitation induced by freeze-thaw events that may become more frequent with global warming. Vessel diameters were l arger in deciduous species compared to evergreens, and in shrubs/trees vs. cushion/mat-forming plants. Vessel length distributions, however, did not d iffer for growth form or leaf character. Vessel density was greater in cush ion/mat-forming species than in shrub/tree species. Deciduous plants showed a greater contribution to total conductivity by relatively larger vessels than evergreens. One of the deciduous species, Vaccinium uliginosum, is pre dicted to be susceptible to freeze-thaw-induced cavitation. These results h ave important implications for future arctic species composition and plant community structure.