Reflectance and phenolics of green and glaucous leaves of Eucalyptus urnigera

On Mount Wellington, Tasmania, Australia, there is an altitudinal cline in the juvenile leaf form of Eucalyptus urnigera from a green phenotype at lower altitudes (from 610 m) to a glaucous phenotype at higher altitudes (up to 1050 m). The objectives of this study were to (1) quantify reflectance of ultraviolet (UV) and photosynthetically active radiation (PAR) for the adaxial and abaxial surfaces of leaves of the glaucous and green phenotypes and (2) to investigate seasonal adjustment in photochemical efficiency (F v/F m) and tannin and flavonol compounds that absorb in UV spectrum. The following two research sites were identified: one at low altitude (at 910 m, solely green phenotype) and one at high altitude (1004 m, solely glaucous phenotype) on the E. urnigera cline. During the experimental period, average summer temperatures were similar at the two sites but in winter, average temperatures were 5-6°C lower and minimum temperatures 0.4-0.7°C lower at the high-altitude site occupied by the glaucous phenotype. Incident PAR was similar at the two sites. Reflectance was higher for glaucous leaves than for green leaves across the light spectrum of UV C (190-280 nm), UV B (280-320 nm), UV A (320-400 nm) and PAR (400-700 nm). Reflectance was significantly higher from the abaxial than from the adaxial surface of leaves. F v/F m was similar for glaucous and green leaves in summer but significantly lower in green than glaucous leaves in winter. F v/F m was significantly lower in winter than in summer for both leaf types. Tannins were significantly higher in green than glaucous leaves but there was no effect of season. Flavonol concentrations were similar for leaves of both types and did not vary with season. We conclude that high reflectance of UV radiation and PAR may confer benefit at the cooler, high-altitude portion of the cline of E. urnigera and that low reflectance of PAR may confer benefit at the relatively warm and densely vegetated, low-altitude portion of the cline of E. urnigera where inter- and intra-specific competition for light is likely to be intense. © CSIRO 2007.