Author:

Keywords:

light quantity, photosynthetic performance, phalaenopsis

Abstract:

Phalaenopsis is one of the most important cultivated ornamentals over the world and is characterized by crassulacean acid metabolism (CAM). This mode of photosynthesis is mainly dependent on nighttime CO2 fixation into malate, which is subsequently processed the following day behind closed stomata. The aim of this study is to investigate the effects of light quantity on photosynthetic performance by analyzing diel CO2 uptake patterns and diel malate turnover under different light treatments. Therefore Phalaenopsis ‘Atlantis’ was grown for 16 weeks under photosynthetic active radiations of either 5, 7, 9 or 11 mol photons m-2 day-1. Gas exchange was monitored on the youngest fully expanded leafs in climate controlled leaf chambers using Li-COR (Li-6400). In addition, leaf samples were taken at critical time points to determine diel malate turnover by a combined enzymatic-spectrometric assay. The results show that total diel CO2 uptake significantly increases from 5 to 7 mol photons m-2 day-1 which can mainly be attributed to a gain in CO2 uptake during early morning and late afternoon. Leaf malate contents are equal for all treatments and no further net carbon gain is realized by supplying higher light levels (i.e. 9 or 11 mol photons m-2 day-1). To conclude, the results indicate nighttime CO2 uptake to be saturated already by supplying 5 mol photons m-2 day-1 but net diel carbon gain can still be realized by supplying extra light during early morning and late afternoon.