Effects of sink removal on leaf photosynthetic attributes of rose flower shoots (Rosa hybrida L., cv. Dallas)

Two experiments were conducted under greenhouse conditions to evaluate the effects of sink removal (flower shoot harvest and debudding) on the gas-exchange capacity (i) of leaves left on the parent shoot after flower shoot harvest and (ii) of flower shoot leaves after flower-bud removal. In the first experiment, gas-exchange measurements were performed on three 5-foliate leaves (leaf 1: uppermost parent shoot leaf, and two leaves inserted just below: leaves 2–3). It was found that, after bud sprouting, the leaf nearest to the young growing shoot (leaf 1) experienced a significant reduction in leaf maximum net CO₂ assimilation rate, A_lm, stomatal conductance, g_s, and transpiration rate, E_l, over time in comparison to the corresponding values observed for leaves 2–3. Leaf water use efficiency, WUE, significantly changed over time, while the ratio of leaf internal to ambient CO₂ concentration, C_i/C_a, was rather conservative throughout the entire shoot growing period. In the second experiment, leaf gas-exchange measurements were performed for adult flower shoots that were either debudded or left intact. Both types of shoots exhibited a similar along-shoot distribution pattern of physiological fluxes, g_s, and WUE. Bud removal did not significantly affect the magnitude of gas-exchange, with the exception of E_l. One week after bud removal, only slight differences were observed for A_lm, g_s and E_l between the two types of shoots. These results suggest (i) that the contribution of the uppermost parent shoot leaf to the assimilates demand of newly growing shoot significantly affects its photosynthetic capacity; and (ii) that flower-bud removal does not change the overall photosynthetic capacity of the flower shoot leaves, which divert the surplus of produced assimilates towards alternative sink organs and plant reserve pools.