In order to gain an understanding of the capacity of severely shaded leaves to be productive in dense canopies, the effects of increased shading on morphology, dry-matter partitioning, and whole-plant net carbon exchange rate (NCER) were investigated on greenhouse-grown Vitis vinifera L. `Chardonnay' grapevines. Vines were subjected to whole-plant shading levels of 0%, 54%, 90%, and 99% of direct sun 3 weeks after potting. Data were collected 8 to 10 weeks after potting. Nonlinear regression was used to investigate the relationship of leaf morphological traits and organ dry weights to increased shading. Leaf size was maintained with increased shading to approximately the 90% shading level, while leaf fresh weight, volume, density, and thickness were immediately reduced with increased shading. Root dry weight was most affected by increased shading, and root to shoot ratio was reduced. When nonlinear regressions were produced for light response curves, light compensation point was reduced by approximately 49% by moderate shading, and 61% by severe shading. Shaded leaves approached the asymptote of the light response curve more quickly, and had reduced dark respiration rates, indicating that the morphological compensation responses by the vine allow shaded leaves to use available light more efficiently. However, the long-term ramifications of reduced root growth in the current year on vines with shaded leaves may be significant.
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