Needle characteristics of Lebanon cedar (Cedrus libani A.Rich.): degradation of epicuticular waxes and decrease of photosynthetic rates with increasing needle age

The evergreen conifer Cedrus libani A.Rich. Is frost- and drought-tolerant and of economic and ecological importance. It has valuable timber and thus has promising potential for cultivation within and outside its natural distribution. Our aim was to determine the morphological and physiological characteristics of C. Libani needle leaves with respect to epicuticular waxes, photosynthetic assimilation rates, and needle age. The study was conducted in the Cedar Research Forest near Elmali, Antalya (SW Turkey) at 1650 m a.s.l. An equation to calculate needle surface area from needle length was created (R2 = 0.96) for adult cedar needles. The form factor for total needle surface area to projected needle surface area was 3.248. The epicuticular wax morphology using scanning electron microscopy showed that the rhomboidal needles of C. Libani possess a dense and intact network of tubular wax crystals, which is common in the family Pinaceae. Wax crystals were found on all sites of the needles and were especially dominant on epistomatal cavities. Wax degradation started in 1-year-old needles and increased with advancing age. The degree of wax degradation gave no indication of significant stress or damage at the study site (e.g., air pollution, extreme drought events). Gas exchange properties were derived from light response and A/ci curves measured in situ in 1-year-old and 2-year-old needles of mature C. Libani trees. Compared to 1-year-old needles, net carbon assimilation rates decreased by about 25% in 2-year-old needles. Assimilation rates and respiration rates were comparable with other conifers, showing no signs of significant stress with needle age. The aging of needles affected both the epicuticular wax structures and the photosynthetic performance. It remains to be clarified to what degree wax degradation influences the decrease of photosynthesis in cedar needles.