Leaf photosynthetic properties and radiation profiles in a rose canopy (Rosa hybrida L.) with bent shoots

Measurements of leaf photosynthetic characteristics, leaf nitrogen (N) content and light were made along the flower shoots and bent shoots of a rose (Rosa hybrida cv. Dallas) canopy managed with the bending technique under Mediterranean greenhouse conditions (Valencia, southern Spain). N-allocation to flower shoot and bent shoot leaves decreased from late-winter to summer. The annual trend of N-leaf, whether expressed per unit leaf area (Nl) or per unit dry mass (Nw, gN gDM−1), followed a quasi-parallel evolution for the two types of shoots with values of Nw 25–30% lower for the bent shoots throughout the year. These results were consistent with the significantly higher values of light-saturated net CO2 assimilation, Alm, and maximum photosynthetic Rubisco capacity, Vlm, observed for the flower shoots. A strong gradient of photosynthetic capacity prevailed along the flower shoots, the uppermost leaves having values of Alm and Vlm, 45% higher than the basal leaves. A similar gradient was observed within the bent canopy, Alm being about 30% higher for the recently bent shoots than for the older ones. Profiles of Alm, Nl and light, reported to their values at the top of the upright and bent canopy, revealed a similar exponential decrease of the three variables. The bent shoots had a higher value of light extinction coefficient and a greater sensitivity of Alm to declining leaf nitrogen content, which explain the low values of the photosynthetic capacity observed for the old bent shoots. The flower shoots, with a marked priority in N-allocation, exhibited a distribution of leaf photosynthetic parameters similar to that previously observed with the traditional pruning techniques.