CANOPY PHOTOSYNTHESIS AND RESPIRATION OF KIWIFRUIT (ACTINIDIA-DELICIOSA VAR DELICIOSA) VINES GROWING IN THE FIELD

Net CO2 assimilation (A) for canopies of kiwifruit (Actinidia deliciosa var. deliciosa) vines enclosed in a whole-canopy cuvette was measured continuously for three periods of 15-20 days during late summer, near Hamilton, New Zealand (latitude 38.2-degrees-S). Canopy A showed an asymptotic response to incident radiation (PAR), saturating at about 1300-mu-mol m-2 s-1 for one vine and about 800-mu-mol m-2 s-1 for two other vines. Radiation interception at low solar angles and low leaf area apparently limited the response of A to PAR. Radiation saturated rates of A were 25-30-mu-mol CO2 m-2 s-1 for one vine, and 12-18-mu-mol CO2 m-2 s-1 for two other vines. At any PAR, canopy A was often lower in the afternoon than in the morning. Canopy respiration averaged 8.9-mu-mol CO2 m-2 s-1 at 12-degrees-C, but increased only 24-34% over the range 7-17-degrees-C. Net daily C gains for the whole canopy, calculated as the temporal integral of A. ranged from -0.8 g C m-2 for a cloudy day (PAR less-than-or-greater-than 450-mu-mol m-2 S- 1) to 6.2 g C m-2 for a day with intermittent cloud. Measurements of gas exchange for single leaves in a leaf cuvette were used to examine the basis of the whole-canopy responses to environmental variables. Partial stomatal closure due to water stress apparently contributed to the afternoon depressions in A, although non-stomatal limitations may also have been involved.