Photosynthetic and fluorescence light responses for kiwifruit (Actinidia deliciosa) leaves at different stages of development on vines grown at two different photon flux densities

Potted kiwifruit, Actinidia deliciosa [( A. Chev.) C.F.Liang et A.R.Ferguso n], vines were grown at two controlled photon flux densities (PFD) of 250 a nd 1100 mu mol m(-2) s(-1) for 110 d to examine ontogenetic and PFD respons es of photosynthesis. Oxygen evolution of detached leaf disks and PFD respo nses of both photosynthesis and chlorophyll fluorescence of attached leaves were measured. A range of leaves, at different nodal positions on the vine s, were used and measurements were repeated over time on the same leaves as they expanded. Results showed that PFD responses of photosynthesis of the high- and low-PFD-grown vines are typical for sun/shade differentiation in P-max and in the PFD for light saturation. The low-PFD-grown vines saturate d at a PFD of 680 mu mol m(-2) (s-1) and had a mean maximum rate of 12.0 mu mol m(-2) s(-1) while high-PFD-grown vines saturated at 960 mu mol m(-2) s (-1), with a mean maximum rate of 15.2 mu mol m(-2) s(-1). There were simil ar differences between the two growth regimes in the electron transport rat e (ETR) but non-photochemical quenching (NPQ) was higher in the low than in the high-PFD-grown vines. Young expanding leaves were characterised by low efficiency of both photochemistry and photosynthesis, low capacity for bot h electron transport through photosystem II and CO2 fixation capacity but b y high respiration and a high capacity for non-radiative thermal dissipatio n. When the leaves had fully expanded, there were marked shifts towards hig her photon yields, ETR and P-max and low respiration and NPQ. In comparison with the effects of growth PFD, ontogenetic effects on development of phot osynthetic competence had greater influences on the PFD responses of photoc hemistry and photosynthesis.