Barrier islands are sentinels for climate change because of the added effects of sea level rise and storms. Shrub expansion has been documented on Virginia’s barrier islands and may be related to climate change. It is important to understand what adaptations allow shrubs such as Morella cerifera (evergreen) and Baccharis halimifolia (deciduous), the dominant woody species, to be more successful as climate shifts. The purpose of our study was to investigate the physiological and structural changes that occur as leaves age, which may affect annual carbon sequestration. Photosynthesis, incident light and chlorophyll levels were quantified on a monthly basis for old, young, and intermediate leaves. Structural differences such as stomatal density, trichome density, leaf thickness, and leaf area were also compared among the three leaf age groups. Leaf C:N ratios were also measured.
Results/Conclusions
The structural differences found in M. cerifera with leaf age included smaller length and area of young leaves and an increased number of stomata on the mid-aged leaves. Baccharis halimifolia new leaves were smaller but showed no significant difference in stomatal density as compared with older leaves. Leaf thickness and trichome density were unaffected by leaf age. The change in photosynthesis with leaf age varied monthly, as did incident light. Incident light on different leaf ages in M. cerifera was less affected by monthly variation and showed consistently less light on old and mid-aged leaves. Photosynthetic rates were unaffected by leaf age. Chlorophyll a, chlorophyll b, and carotenoids were affected by both monthly change and leaf age. Physiological variations were observed with differences in leaf age, as were structural differences but to a lesser extent. Leaf age did impact physiological differences but is less important structurally. The ability to symbiotically fix nitrogen, higher photosynthetic rates and chlorophyll contents, may explain the relative expansion of the evergreen M.cerifera as compared to the deciduous B. halimifolia on Virginia’s barrier islands.