Production and postproduction irradiance affects acclimatization and longevity of potted chrysanthemum and poinsettia.

Production irradiance levels on growth, light compensation point (LCP), dark respiration (DR), and interior longevity of potted chrysanthemum (Demfranthema grandiflora Tzvelev. CVS. Iridon and Mountain Peak) and poinsettia (Euphorbia pulcherrima Wind. CVS. Annette Hegg Dark Red and Gutbier V-10 Amy) were determined. LCP and DR were measured at anthesis and during acclimatization to interior conditions (10 µmol·s -1 ·m -2 ). Days to flowering, inflorescence diameter, total chlorophyll, and interior longevity of chrysanthemum increased when maintained at a mean maximum photosynthetic photon flux density (PPFD) of 500 µmol·s -1 ·m -2 compared to plants shifted to 300 or 100 µmol·s -1 ·m -2 8 weeks after planting. LCP and DR were highest at anthesis and were reduced 38% and 49%, respectively, for chrysanthemum and 19% and 42%, respectively, for poinsettia within 3 days in interior conditions. Chrysanthemum plants shifted to 300 µmol·s -1 ·m -2 during production had lower LCP and DR rates at anthesis and throughout time in interior conditions compared to plants maintained at 500 µmol·s -1 ·m -2 . The acclimatization of chrysanthemum to reduced production PPFD is of little significance because interior longevity is reduced. No differences were found in the LCP or DR of poinsettia or chrysanthemum cultivars that differ in interior performance, demonstrating that these physiological characteristics are not good indicators of interior longevity for chrysanthemum and poinsettia. Foliage plants produced under reduced light or fertilizer levels lose fewer leaves once plants are moved indoors (Conover and Poole, 1975, 1981, 1984; Fails et al., 1982; Pass and Hartley, 1979). This process is referred to as acclimatization and can be accomplished by growing plants under specific light intensities (Conover and Poole, 1975) or providing an acclimatization pe- riod during the final 6 to 8 weeks of production. Conover and Poole (1984) have emphasized that the use of acclimatized fo- liage plants increases the potential for continued plant growth and aesthetic quality indoors. Acclimatization of foliage plants has been associated with a low LCP and DR rate, and increased photosynthetic efficiency at low irradiances (Fonteno and McWilliams, 1978; Mbah et al., 1983; Pass and Hartley, 1979). Fonteno and McWilliams (1978) observed that dark respiration was reduced 50% to 70% in four foliage plant species during acclimatization and con- cluded that respiration rate must be a major factor in acclima- tization. Pass and Hartley (1979) suggested that the reduction in LCP and DR during acclimatization may result from the change in the relative importance of the two components of respira- tion—maintenance and growth respiration. Lower maintenance respiration may be responsible for greater efficiency at lower irradiance levels, as observed in three foliage plant species (Pass and Hartley, 1979). Little information has been developed regarding the factors affecting longevity of flowering potted plants. Staby and Kof- ranek (1979) showed that termination of fertilizer 2 weeks be- fore anthesis of 'Annette Hegg Supreme' poinsettia decreased leaf drop under interior conditions. Scott et al. (1984) demon- strated that poinsettia leaf drop was reduced when plants were produced wit low levels of slow-release fertilizer. Micronutri-