Photon flux density dependence of carbon acquisition and demand in relation to shoot growth of kiwifruit (Actinidia deliciosa) vines grown in controlled environments

Kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson] vines were grown in four controlled photon flux densities (PFDs) from 250 to 1100 mu mol m(-2) s(-1) for 130 d starting from pre-budbreak to measure relationships between shoot growth and carbon (C) demand and to assess the effect of PFD on these processes. Leaf area, stem length, photosynthesis and respiration rates were measured on the same leaves at regular intervals. From daily C acquisition and accumulation in biomass, the net C balance per cane was determined throughout the experiment. High-PFD-grown vines had 13% more leaf area, 250% more leaf biomass and 30% more stem biomass than low-PFD-grown vines. High-PFD-grown vines also partitioned relatively more biomass to photosynthetic tissue than to supporting stem tissue compared with low-PFD-grown vines. Rates of net photosynthesis were highest on vines grown at 800 mu mol m(-2) s(-1), but respiration rates were highest in high-PFD-grown vines. Vines grown at 1100 mu mol m(-2) s(-1) had a net gain of 119 g sh(-1) and 53 g sh(-1) at 250 mu mol m(-2) s(-1), of which 46 and 58%, respectively, was used in shoot biomass growth. Net C balance was negative for 30 d after budbreak. Over 130 d, high-PFD-grown vines produced a total surplus of 64 g sh(-1), while low-PFD-grown vines produced 22 g sh(-1). Results demonstrate that irradiance has no effects on developmental processes but has marked effects on vegetative growth rates of kiwifruit vines. Underlining this, the C economy of these shoots is highly and quantitatively dependent on the PFD during growth.