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

Abstract

Potted kiwifruit, Actinidia deliciosa [(A.Chev.) C.F.Liang et A.R.Ferguson], vines were grown at two controlled photon flux densities (PFD) of 250 and 1100 mol m^–2 s^–1 for 110 d to examine ontogenetic and PFD responses of photosynthesis. Oxygen evolution of detached leaf disks and PFD responses of both photosynthesis and chlorophyll fluorescence of attached leaves were measured. A range of leaves, at different nodal positions on the vines, 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 saturated at a PFD of 680 mol m^–2 s^–1 and had a mean maximum rate of 12.0 mol m^–2 s^–1 while high-PFD-grown vines saturated at 960 mol m^–2 s^–1, with a mean maximum rate of 15.2 mol m^–2 s^–1. There were similar differences between the two growth regimes in the electron transport rate (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 both electron transport through photosystem II and CO₂ fixation capacity but by high respiration and a high capacity for non-radiative thermal dissipation. When the leaves had fully expanded, there were marked shifts towards higher photon yields, ETR and P_max and low respiration and NPQ. In comparison with the effects of growth PFD, ontogenetic effects on development of photosynthetic competence had greater influences on the PFD responses of photochemistry and photosynthesis.