| Photosynthetic carbon production and utilization was investigated for main-stem and sympodial leaves at main-stem nodes 8, 10, and 12 within a field-grown cotton (Gossypium hirsutum L.) canopy. Net photosynthesis of sympodial leaves increased to a maximum just prior to anthesis of their subtended flower. Thereafter, photosynthesis declined throughout the boll-filling period and suggested that sympodial leaves were limited in their capacity to produce sufficient photosynthate for boll growth.;Simulated carbon budgets for individual sympodial leaves and fruiting branches indicated that bolls at main-stem node 8 required over 60% import of carbon to sustain measured growth rates. Carbon import requirements for the first three fruiting positions at main-stem node 10 were 49%, 37%, and 21%, respectively. The deficiency of carbon necessitated substantial translocation of carbon from adjacent leaves and leaves above or below the main-stem node. This was confirmed with short-term studies of ;The contribution of photosynthate from the bracts and capsule walls was evaluated as alternative sources of carbon. Bracts reached a peak photosynthesis of 2.1 ;Nitrogen deficiency limited leaf area expansion and dry matter partitioning to leaves, stems, and reproductive structures. These limitations were not, however, associated with decreased rates of single-leaf or whole-canopy photosynthesis. Such observations suggest that nitrogen deficiency altered the whole-plant carbon balance in cotton via either increased respiration or increased partitioning of dry matter to the roots. |
