No abstract

Photosynthetic activities of the sago palm (Metroxylon sagu Rottb.) were studied to find out its sensitivity to changes in ambient air temperature. The minimum ambient air temperature designed for the experiment was 25-29 • C, while the higher end was 29-33 • C. Several photosynthetic parameters were studied to support our analysis in sago photosynthetic activity, including diurnal leaf gas exchange, assimilation rate vs. CO 2 concentration, leaf greenness, leaf chlorophyll content, and photosynthetic rate vs. irradiance. We found that sago palm photosynthetic activity tends to be more sensitive to minimum than to maximum ambient air temperature. The plants exposed to higher air temperatures had dark green leaf color associated with higher rates of diurnal photosynthesis, chlorophyll content, and rubisco limited photosynthetic activity. They also exhibited higher trend in optimum irradiance absorption level. Consequently, maximum light energy dissipation occurred at higher temperatures.

Sago palm (Metroxylon sagu Rottb.) photosynthetic performance was evaluated under drought conditions through leaf gas exchange and chlorophyll a fluorescence measurement. Drought has an impact on sago palm's leaf gas exchange parameters and its chlorophyll fluorescence of PSII. Stomatal limitations were found to be the main factor limiting photosynthetic activities of sago palm under drought conditions. Photosynthetic rate decreased following the inhibition in the PSII reaction center. Early detection of interference upon the efficiency of the PSII reaction center due to drought stress was recorded by chlorophyll a fluorescence measurement.Abbreviations: CF/I-light response curve of chlorophyll a fluorescence, C i -intercellular CO concentration, E-transpiration rate, E opt -optimum irradiance, ETR-electron transport rate, ETR maxmaximum electron transport rate, g s -stomatal conductance, I max -maximum irradiance, NPQnon-photochemical quenching, P N -net photosynthetic rate, P N /I-light response curve of net photosynthetic rate, P N (Imax) -maximum value of P N obtained at maximum irradiance, WUEwater use efficiency, Y (II)-effective quantum yield of PSII, α-asymptotic photosynthetic efficiency, Φ (Icomp-I200) -quantum yield at the range between light compensation point and 200 µmol m −2 s −1 irradiance.