GAS-EXCHANGE OF OIL PALM IN RELATION TO LIGHT, VAPOR-PRESSURE DEFICIT, TEMPERATURE AND LEAF AGE (REPRINTED FROM FUNCTIONAL ECOL, VOL 7, PG 97, 1993)

Leaf gas exchange in oil palms (Elaeis guineensis Jacq.) was measured in the field over a range of photon fluxes, leaf temperatures and leaf -air vapour pressure difference (VPD). Results showed no differences i n leaflet photosynthesis within one frond, but a reduction depending o n frond age. For fronds of the same age, between-tree variation was lo w. The light saturated rate of net CO2 assimilation was 20 mumol m-2 s -1 when photosynthetically active radiation (PAR) exceeded 1100 mumol m-2 s-1. Apparent quantum yield averaged 0.051 mol mol-1. When leaf te mperature increased from 30-degrees-C to 38-degrees-C, net CO2 uptake showed no variation as transpiration rate and stomatal conductance inc reased slightly. A small increase in VPD induced rapid stomatal closur e and consequently a reduction in the transpiration rate. A VPD greate r than 1.8 kPa was required before photosynthesis was reduced via stom atal closure in the case of plants growing in a soil with adequate wat er supply.