EFFECT OF LIGHT AND TEMPERATURE ON PHOTOSYNTHESIS, ELONGATION RATE AND CHLOROPHYLL CONTENT OF NELUMBO-LUTEA (WILLD) PERS SEEDLINGS

Petiolar photosynthetic carbon assimilation (PCA) rates, elongation rates, and chlorophyll (Chl) content were assessed in seedlings of Nelumbo lutea (Willd.) Pers. grown in aseptic liquid culture under variable photon flux density (30-910 mumol m-2s-1) and temperature (3-30-degrees-C) conditions. When plants were grown under standard conditions (23-degrees-C, 100 mumol m-2s-1 photon flux density) and exposed to short-term changes in light and temperature regimes, maximum PCA (approximately 650 mumol C g-1 Chl a h-1) occurred at 20-degrees-C and a photon flux density of 500 mumol m-2s-1. Longer term growth experiments (10 day) conducted under a variety of temperature: illumination regimes demonstrated that at all temperatures PCA rates increased curvilinearly up to a photon flux density of 560 mumol m-2s-1, then decreased gradually as light intensity increased. At all photon flux densities, the highest seedling PCA was obtained at 20-degrees-C. Petiole elongation rates increased up to 560 mumol m-2s-1 and declined at higher photon flux densities. Overall elongation rates were greatest at 30-degrees-C, followed by 20-degrees-C and 10-degrees-C. Chlorophyll content decreased as photon flux density increased in seedlings grown at 30-degrees-C and 20-degrees-C, but at 10-degrees-C increased up to 350 mumol m-2s-1 and then declined at higher photon flux densities. The collective data suggest that PCA by elongating petioles, may contribute to seedling growth, even under relatively cool, dark conditions near the sediment-water interphase.