Effects of light, temperature, defoliation, and fruiting on carbon assimilation and partitioning in potted cranberry

Abstract

Carbohydrate supply has been hypothesized to limit fruit set in cranberry (Vaccinium macrocarpon Ait.), however the limitations to carbon gain throughout the season are currently unknown. These experiments investigated the effects of light, temperature, fruit presence, and defoliation on carbon production and partitioning in potted cranberry. Fruiting and vegetative uprights (short vertical stems which bear fruit biennially) reached similar asymptotes with respect to light response, but fruiting uprights reached saturation at a lower light intensity than vegetative uprights. Runners (diageotropic vegetative stems) had a lower asymptote, higher light compensation point, and greater rate of dark respiration than uprights. Temperature had little effect on net carbon exchange rate of uprights or runners. Before new growth, defoliation did not affect the concentration of total nonstructural carbohydrates in the vegetative uprights, or the partitioning of soluble carbohydrates to starch, even though uprights with lower leaf areas had higher net CO2 assimilation. At fruit set and again at fruit maturity, defoliation reduced total nonstructural carbohydrate concentration, while net CO2 assimilation was not affected. Carbohydrate production and partitioning within an upright was unaffected by the presence of a single fruit throughout the experiment.