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Abstract
Leaf-level gas exchange was measured in response to temperature, vapor pressure deficit (VPD), photosynthetic active radiation, and daily dry-down periods from ten container-grown Rhododendron maximum plants. Diurnal patterns of net photosynthesis, stomatal conductance, and transpiration where also measured and showed a morning increase until it reached a peak during midday, followed by a decline during the evening in all age classes. For all measurements, the three different age classes varied significantly, with the one-year-old foliage exhibiting the highest rates of photosynthesis, stomatal conductance, and transpiration. Leaf water potential measurements during a dry-down period indicated R. maximum is sensitive to water stress. Rhododendron maximum leaves require mid-temperature ranges, low VPD levels, and low light intensities to reach maximum mean net photosynthetic rates, stomatal conductance, and transpiration rates. Stomatal conductance increased with increasing net photosynthesis, and transpiration increased linearly with stomatal conductance when induced stress was not a factor.