Light intensity influences growth and leaf physiology of Aucuba japonica 'Variegata'.
Andersen P.C. | Knox G.W. | Norcini J.C.
Leaf physiology and growth parameters of Aucuba japonica (Thunb.) cv. Variegata were assessed under conditions of full sun (photosynthetic photon flux = 1531 to 2073 micromole-m-2-s-1) and under shadecloth (light transmittance of 69%, 47%, and 29% full sun) over 2 years. Two days after treatment initiation, net CO2 assimilation (A) was proportional to light level, although stomatal conductance to water vapor (gs) was not influenced by shading. Subsequently, A, gs, transpiration rate, and water use efficiency of 100% sun-grown plants were often < 50% that of shade-grown plants. After 1 month of exposure to 100% sun, leaves were chlorotic and necrotic; plant appearance was normal for plants grown under shadecloth. The growth index and total, leaf, stem, and root dry weights were inversely related to light level. Relative water content and chlorophyll concentration in leaves that had expanded before treatment initiation were reduced with increasing levels of irradiance, but these variables were not altered in leaves produced after treatment initiation. Plants from all treatments experienced dieback when transplanted to the field under conditions of full sun. We conclude that A. japonica is shade obligate, performing best with exposure to less than or equal to 47% of full sunlight.
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