Influence of fruit sink strength on the distribution of leaf photosynthetic traits in fruit-bearing shoots of pepper plants (Capsicum annuum L.)

The influence of individual fruit sink strength and the acclimation to light on leaf photosynthetic attributes of greenhouse-grown sweet pepper (Capsicum annuum L., cv. Cornado) plants was investigated under Mediterranean glasshouse conditions during a winter–spring crop cycle. The photosynthetic parameters (net CO2 assimilation, A, and stomatal conductance, gs) of source leaves close to fruits at different stages of growth were measured under controlled levels of photosynthetic photon flux density, air CO2 concentration and leaf temperature. The light profile within the canopy was determined under the prevailing climate glasshouse conditions. Data were analysed and interpreted by distinguishing five classes of source leaves, each class corresponding to a given growth stage (i.e. sink strength) of the proximal fruit. Whatever the amount of light reaching the leaves (e.g. leaf area index of 0.8 and 2.5 mleaf2 mground−2), those inserted near a fruit at near maximum growth rate exhibited the highest light-saturated values of A (Am) and gs (gsm) followed by leaves inserted near an open flower. Leaves inserted near a red ripe fruit or near a recently harvested fruit presented the lowest values. A similar hierarchy was observed for organic N-leaf content, expressed either on a leaf area basis or dry weight basis, while the residual (non-photosynthetic) N-leaf content was found to be rather conservative. Differences in Am and gsm among the leaf classes, and the lower attribution of photosynthetic N to leaves subjected to a low sink demand, suggest that leaf photosynthetic capacity along a fruit-bearing shoot is mainly driven by the sink demand of the most proximal fruit, and not by light acclimation.