Influence of leaf position, fruit and light availability on photosynthesis in different chestnut genotypes

The effects of leaf position in the crown, light availability and the presence of fruit on leaf net photosynthesis (Pn) were evaluated in a chestnut orchard located in central Italy. The study was carried out on Castanea sativa Mill. "Marrone di Stroncone" ecotype, spread in the Umbria Region, and on an interspecific hybrid Castanea crenata x Castanea sativa, cv. Marigoule. "Marrone di Stroncone" had higher Pn than Marigoule. In both genotypes, during the growing season the Pn changed in the different phenological stages and, in particular, it was higher during the fruit growth period. From July to October the part of the shoot with higher Pn progressively shifted from the base to the tip of the shoot. During the day, Pn was high during the morning, then progressively decreased in the afternoon. The closeness of fruit increased the Pn of the leaves on the shoots exposed to full sun light, above all during the morning, but did not significantly influence the leaf chlorophyll (Chl) and carbohydrate content. Light saturation for the Pn was relatively high and there was a drastic reduction in Pn in leaves which, due to their position, during the day intercepted a PPFD lower than 300-400 mu mol photon m(-2)s(-1). The shaded leaves were thinner than sunlit ones (about -26%). Both the epidermic and mesophyll tissues were higher in sunlit leaves. Also the "density" of cells was higher in sunlit leaves. Morpho-anatomical and physiological adaptations allow the chestnut to optimise its use of the limited radiant energy available, but shading greatly reduces the productivity. From the results it is affirmed that studies which consider photosynthetic assimilation must take into account the genotype, time, leaf position and influence of the fruit. In order to increase the efficiency of the tree, it is important to ensure optimal conditions (light interception, water and nutrient availability, leaf protection, etc.), above all during the times in which the demand for assimilates is high.