LIGHT ACCLIMATIZATION OF FICUS BENJAMINA L

Leaf abscission often occurs on weeping fig (Ficus benjamina L.) plants after transfer from production nurseries to interior locations, thus reducing plant quality and value. Studies were designed to determine the effect of light preconditioning on acclimatization potential of plants to low light interior environments.; Anatomical and physiological features of sun and shade adaptation in full sun-grown and 75% shade-grown leaves were observed. Sun-grown leaves were thicker than shade-grown leaves, had 2 layers of well developed palisade cells, a vertical alignment of chloroplasts, and a greater stomatal density. Shade-grown leaves were thinner than sun-grown leaves, had only 1 layer of palisade cells, had more stomata per leaf, and chloroplasts were larger and dispersed throughout the palisade cells. Sun-grown leaves were smaller, folded along the midrib, and both leaves and branches were more vertically oriented, whereas shade-grown leaves were larger, flatter, darker green, and both leaves and branches were more horizontally oriented. These characteristics of shade-grown plants are believed to maximize light interception. The variations in the two leaf types suggest weeping fig leaves can potentially adapt to a wide range of light environments.; Leaves were measured to determine rates of net photosynthesis (Pn), dark respiration (Rd), and light compensation points (LCP). Light saturation was near 350 (mu)E m('-2) s('-1) for sun-grown and 200 (mu)E m('-2) s('-1) for shade-grown leaves. At photosynthetically active radiation (PAR) levels above 110 (mu)E m('-2) s('-1), Pn of sun-grown leaves was higher than shade-grown leaves while the reverse was true at PAR levels below 77 (mu)E m('-2) s('-1). Rd and LCP of shade-grown leaves were 50% of sun-grown leaves. These results indicate that shade-grown leaves have greater photosynthetic potential at low PAR than sun-grown leaves and suggest potential for photosynthetic adaptation to other light regimes.; Plants were placed in a simulated interior environment (SIE) under 20 (mu)E m('-2) s('-1) for 12 weeks, after being grown in full sun (S-SIE), 75% shade (Sh-SIE), or full sun followed by 8 weeks acclimatization under 75% shade (A-SIE). Leaves of Sh-SIE and A-SIE were better adapted photosynthetically than S-SIE due to higher Pn at lower PARs, and lower LCPs. Anatomical observations also revealed chloroplast reorientation, increase in size, and increase in intensity of staining in treatments A-SIE and S-SIE. Total dry matter did not increase during the 12 week SIE phase, although plants in S-SIE were found to shift distribution from roots to leaves for production of new shade foliage. All plants in the SIE remained of high quality throughout the experiment and showed a net increase in the number of leaves. Photosynthetic and anatomical modifications occurring in weeping fig placed in low light contribute to shade adaptation.