Seasonal variation in the photosynthetic capacity of a willow (Salix cv. Aquatica gigantea) canopy. 2 Comparison of the structure and function of chloroplasts at different levels in the canopy

Development of leaf chloroplast ultrastructure at five levels in a willow (Salix cv. Aquatica gigantea) canopy was followed during one growing season in the field. Changes in chloroplast ultrastructure were compared with the rate of CO(2) uptake of the same leaves. The highest rates of CO(2) uptake were recorded in young leaves exposed to full available sunlight. In these leaves, the area of the grana stacks was less than 20% of the total chloroplast area and the degree of thylakoid stacking was less than 1.5. The chloroplasts of these leaves contained large amounts of starch and small amounts of plastoglobuli. As the canopy grew and the leaves in the lower parts of the canopy became shaded, the structure of the chloroplast thylakoids gradually changed. In leaves at the two lowest levels of the canopy, the degree of stacking at the end of the growing season was close to 2 and correspondingly the rate of CO(2) uptake was low. The areas of grana stacks and plastoglobuli in these chloroplasts increased and were about 30 and 10% of the chloroplast area, respectively, by the end of the growing season. The increase in the degree of thylakoid stacking was caused by increased biosynthesis of grana lamellae, which in general were thinner than the lamellae of young leaves. The length of the stroma lamellae did not change with leaf age. Morphometric measurements showed that the structure of the chloroplasts in leaves 160 cm above ground was dynamic and responsive to environmental conditions so that photosynthetic capacity remained high for 7 weeks despite an increase in leaf shading.     

Seasonal variation in the biomass and non-structural carbohydrate content of fine roots of teak (Tectona grandis L. f.) plantations in a dry tropical region

Seasonal variation in the biomass and total non-structural carbohydrate content (TNC) of fine roots of teak (Tectona grandis L. f.) were studied in 19- and 29-year-old plantations in a dry tropical region. Fine root TNC content was highest during the dry summer (May), and lowest in the early part of the rainy season (July). Generally, seasonal trends in TNC content were the opposite of those in fine root biomass. The TNC concentration of roots increased with diameter and decreased with soil depth. In the 19-year-old plantation, fine root TNC content was approximately 12% higher than in the 29-year-old plantation.