Response of in vitro Cultured Palm Oil Seedling Under Saline Condition to Elevated Carbon Dioxide and Photosynthetic Photon Flux Density

Abstract

Salt stress elicits various physiological and growth responses of oil palm. A laboratory experiment was conducted to determine the responses of oil palms cultured in vitro under varying salinity levels (0, 85.5, 171.11, 342.21 and 684.43 mM NaCl) to elevated CO₂ (1000 μmol CO₂/mol) and PPFD (100±5 μmol m^-2 s ^-1) in terms of growth characteristics, pigment contents and photosynthetic abilities. After 14 days of culture, net photosynthetic rate (μmol CO₂ m^-2 s ^-1) of oil palms across varying salinity levels was 5.33 times higher than those cultured under ambient CO₂ (380±100 μmol CO₂ /mol) and PPFD (50±5 μmol m^-2 s^-1). At increased net photosynthetic rate (elevated CO₂ and PPFD), despite having no significant difference in pigment contents (chlorophyll a, chlorophyll b, total chlorophyll and carotenoid) between different CO₂ and PPFD levels, dry weight and percent dry matter were 0.26 and 0.11 times higher, respectively, as compared to those cultured under ambient CO and PPFD. In the same elevated CO and PPFD level, across all salinity levels, stomatal conductance was 0.30 times lower than those cultured under ambient CO and PPFD. At reduced stomatal conductance (elevated CO₂ and PPFD), transpiration rate was also reduced by 0.30 times. Thus with increased net photosynthetic rate and reduced transpiration rate, water use efficiency was increased by 7.22 times, across all salinity levels, than those cultured at ambient CO₂ and PPFD. These were considered essential for NaCl produces iso-osmotic stress.