MEASUREMENT OF CANOPY GAS-EXCHANGE OF KIWIFRUIT VINES USING A SUITE OF WHOLE-CANOPY CUVETTES

A system tor estimating net CO2 assimilation and H2O transpiration simultaneously for the canopies of four kiwifruit (Actinidia deliciosa var. deliciosa) vines in the field is described. The canopy of each vine was enclosed in an open system gas exchange cuvette, with volume of ca 26 m3 and basal floor area of ca 10 M2 . A computer-controlled sampling and logging system enabled one set of analytical instruments to be used for measuring sequentially the difference between ambient CO2 and H2O partial pressures and those within each cuvette. Air flowing into each cuvette was dispersed upwards and outwards, whereas air exited primarily through a slit in the floor. Average CO2 partial pressures at various positions within the cuvette varied less than 0.05 mumol/mol during a 600 sec logging period, indicating adequate air mixing within the cuvette. The equilibration time for canopy net CO2 assimilation (A) to respond fully to a large change in irradiance was about 120 sec. The equilibration time for the measurement system after changing cuvettes was about 60 sec. Real-time data analysis of gas exchange dynamics and graphical display of data enabled rapid decisions regarding system settings during a normal experimental period. On some days, large diel fluctuations in ambient CO2 partial pressures caused significant short-term variability in measured differential CO2 partial pressures, although long-term (e.g. 8 hr) integrals were valid. Effects of different canopy leaf areas on diet dynamics of net A and net H2O transpiration (E) were clearly illustrated. Mid-day declines of net A were also demonstrated.