Ecophysiology and Comparative Foliar Micromorphology of Big-Bracted Cornus Selections

The most common Cornus taxa in the nursery industry are those from the big-bracted tribe.  Within this group a substantial amount of variation in environmental tolerances has been reported.  Our objectives were 1) to determine the variation in a suite of foliar micromorphology parameters and gas exchange for seedlings of C. kousa and C. florida grown under controlled environment conditions and for three related grafted selections: C. florida ‘Cherokee Princess’, C. kousa ‘National’ and C. florida x C. kousa hybrid Constellation® grown in outdoor conditions, and 2) to determine variation in stomatal number for a range of eight established big-bracted selections, and a C. mas selection for comparison, in order to better understand their response to stresses and performance in landscapes.  Of the controlled-environment produced-plants, the number of stomates per unit area was 60% greater for C. florida than for C. kousa, 83.5 and 51.5, respectively.  However, area per individual stomate and total stomatal area per leaf, an integrated value of stomate number and stomatal complex area, were greater for C. kousa.  Epidermal cell thickness was greater for C. kousa than C. florida.  The pattern of wax deposition on the abaxial surface differed between C. kousa and C. florida.  The reduced total stomatal area per leaf and abaxial wax may be an adaptation to protect C. florida, which is considered drought-adverse.  The number of stomates per unit leaf area varied significantly among the established big-bracted selections from a low of 51.8 for C. mas ‘Spring Sun’ to a high of 209.6 for C. x Constellation®.  In general, the C. kousa cultivars and the C. kousa x C. florida hybrids had a greater number of stomates per unit leaf area than did C. mas ‘Spring Sun’ and C. kousa seedlings.  The hybrids had a range of stomates, from 209.6 to 72.8 for Constellation® and Ruth Ellen®, respectively.  Among Constellation®, ‘Cherokee Princess’ and ‘National’, Constellation® had the greatest number of stomates.  The average stomatal complex size and average total stomatal area were greater for Constellation® and National than for ‘Cherokee Princess’. Constellation® had greater photosynthetic rate, stomatal conductance, and transpiration rates than both C. kousa ‘National’ and C. florida ‘Cherokee Princess'.  Among the two species growing the controlled environment, C. florida had a greater photosynthetic rate, stomatal conductance, and transpiration rate than C. kousa.