Postdoctoral Research Associate University of Florida Lake Alfred, Florida
Body of Abstract: Competing demands for carbon and essential nutrients from shoots, roots, and reproductive structures govern the dynamics of carbon fixation and transport in perennial species. Despite the critical role of these dynamics in the growth of perennial species, their impacts on carbon fixation and transport remain unclear. Therefore, we conducted a study to investigate carbon fixation and translocation in apical and basal leaves of citrus branches at different phenological stages, including mature branches, mature branches with new flushes, and mature branches with young shoots and new leaves. To measure carbon fixation, we employed a rapid A/Ci response gas exchange method, and radioisotope tracing was used to measure leaf export. Our results showed a decline in the efficiency of photosynthesis with the advancement of growth phenology, as evidenced by a decrease in the maximum rate of carboxylation (Vcmax) and electron transport rate for RuBP regeneration (J1200). Furthermore, we observed that basal leaves exported more carbon than apical leaves in mature shoots with no new shoot growth, while the trend was reversed when the mature shoot produced new shoots, suggesting more carbon export from apical leaves towards new shoots. Additionally, our study found that young leaves had less carbon export than mature ones, regardless of their position on the branch. The study provides insights into how the efficiency of photosynthesis and carbon export from different leaves vary with the advancement of growth phenology and highlights the importance of considering the phenological stage of tree branches when investigating these dynamics.