Temperature and photon flux density effects on carbon assimilation in cranberry

The effect of temperature and radiation on cranberry (Vaccinium marcrocarpon Ait.) photosynthesis is not well understood. When C3 plants such as cranberry are exposed to optimal temperature and saturating light, the rate of net CO₂ assimilation is almost always limited by rubisco due to the tendency for photorespiration. It is not clear whether new cranberry cultivars, whose fruit yields are greater than those of older cultivars, support the increased fruit load by the minimization of photorespiration or by having a larger photosynthetic capacity and better partitioning of assimilates between vegetative and reproductive sinks. This project evaluated the effect of temperature and photosynthetic photon flux density (PPFD) on net CO₂ assimilation (A) in two old cultivars ('Early Black' and 'Stevens') and two new cultivars ('Crimson Queen' and 'Mullica Queen'). Gas exchanges of upright shoots were measured and data for all cultivars were taken at two cuvette temperature regimes (20 and 30°C). At 30°C, 'Mullica Queen' reached a net CO₂ assimilation rate of 25 μmol m^-2 s^-1 at PPFD of 600 μmol m^-2 s^-1. Dark respiration ranged from -10.75 μmol m^-2 s^-1 at 30°C in 'Stevens' to 10.14 μmol m^-2 s^-1 at 20°C in 'Crimson Queen'. The highest light compensation point was 65.09 μmol m^-2 s^-1 with 'Early Black' and the lowest was 9.96 μmol m^-2 s^-1 with 'Stevens' at 20°C. The fact that 'Crimson Queen' reached a higher asymptote compared to the old cultivars at 30°C indicates a higher quantum yield and can capitalize on existing light microclimates in the field. In a crowded canopy these differences could be significant with respect to net CO₂ assimilation.