INTERACTIONS OF LEAF AGE, FRUITING, AND EXOGENOUS CYTOKININS IN SANGIOVESE GRAPEVINES UNDER NONIRRIGATED CONDITIONS .2. CHLOROPHYLL AND NITROGEN-CONTENT

The interactions of leaf age, chlorophyll, and nitrogen content, together with modifications induced by fruiting and kinetin application, were investigated in horizontally trained shoots of field-grown Sangiovese (Vitis vinifera L.) grapevines. Dry weight per unit leaf area (W) increased over a leaf age span of five months and showed a curvilinear relationship with Pn rates reported earlier in the companion paper. Regression of chlorophyll per unit leaf area versus leaf age was curvilinear, maximum chlorophyll content being recorded at 80 to 90 days of age. The correlation of chlorophyll versus Pn was not significant within any shoot zones. Leaf nitrogen content plotted against leaf age exhibited different patterns depending on the unit chosen to express the data. An exponential negative regression was found when leaf N was given as percentage of dry weight. By contrast, a cubic regression fit the data when leaf N content was on a leaf-area basis. Nitrogen accumulated in the leaf up to about 45 to 50 days of age, and then an export pattern set in. Correlation of N versus Pn within each shoot zone was significant only for basal mature leaves when nitrogen data were expressed on a dry-weight basis, whereas the data for median leaves were significant when given on a leaf-area basis. Leaf age effects were not modified by crop level or kinetin. These results indicate that caution is needed when trying to use W, chlorophyll, and nitrogen as indicators of photosynthesis capacity for grapevine leaves of varying age