Seasonal changes in photosynthetic activity and carbohydrate content in leaves and fruit of three fig cultivars (Ficus carica L.)

Abstract

This study was carried out to investigate the seasonal photosynthetic capacity of ‘Kalamon’, ‘Fracasana’ and ‘Mission’ fig cultivars and the effect of chlorophyll (Chl), nitrogen, specific leaf weight (SLW) and leaf anatomy on net photosynthesis rate (Pn). The seasonal changes in carbohydrate concentrations in leaves and fruit were also studied. Pn and stomatal conductance (gs) in leaves were measured in the field using an infra-red gas analyser. Soluble sugars were analyzed in leaves and fruit using a high-performance liquid chromatographic system, and starch with an enzymatic method.The concentration of Chl (a+b) increased rapidly up to early June, when the leaves reached their maximum area, then started decreasing slowly. The main soluble sugars found in both fig leaves and fruits were sucrose, glucose and fructose. Leaves of all cultivars contained much more sucrose than other sugars. Soluble sugar and starch concentrations increased until leaves reached their maximum area, decreasing thereafter. This period (late May) coincided with the emergence of inflorescences. Leaves of ‘Kalamon’ had higher concentrations of sucrose, fructose, total soluble sugars and starch than did the other cultivars.In contrast to leaves, in fruits the sucrose concentration was much lower than that of other sugars throughout the periods of fruit development and maturation. No significant differences in sugars were found between the cultivars during the period of fruit development, but mature fruit of ‘Kalamon’ and ‘Mission’ had higher concentrations of all sugars than did those of ‘Fracasana’.Pn increased rapidly from leaf emergence, reaching maximum values for all cultivars at full leaf expansion (FLE), then decreased and increased again during the period of fruit maturation. ‘Kalamon’ had higher Pn than the other cultivars. This is probably due to the higher SLW, nitrogen and Chl concentrations, the greater palisade parenchyma and leaf thickness, as well as to the higher gs found in ‘Kalamon’ compared to the other cultivars.