Increasing the efficiency of photosynthesis in sugarcane canopies is the key for improving crop yield. Herein, we evaluated the photosynthetic performance along the canopy of ten sugarcane cultivars and three Saccharum species. Canopy morphological traits were evaluated, and leaf gas exchange was measured in the first (sun-exposed, +1) and the fourth (shaded, +4) fully expanded leaves and under low- and high-light conditions. Similar photosynthetic capacity was found in leaves +1 and +4 under high light in genotypes with a high leaf area index and a high fraction of the sky blocked by the foliage (> 85%). Interestingly, such canopy characteristics cause low light availability to leaves +4, suggesting the photosynthetic acclimation of these leaves to self-shading in some genotypes. We highlight IACCTC06-8126 and CTC4 as those genotypes with higher canopy photosynthetic capacity, presenting high leaf area, high photosynthetic rates in sun-exposed leaves, and high responsiveness of shaded leaves to increasing light availability.
The effects of a high temperature on leaf photosynthetic response of Lupinus albus, a species native from the Mediterranean zone, were studied under varying tissue water status and irradiance (/). At leaf temperatures optimal (25 °C) or near-optimal (15 ®C) for carbon assimilation in lupins, photosynthetic capacity (P^) was decreased at leď relative water content (RWC) around 60 %. The temperature above the optimum (e g. 35 oC) decreased at high RWC (80 %). Irrespective of the leaf water status the optimum leaf temperature for in lupins was around 25 "C. The inhibition of P^ by lupin leaf discs at 35 °C was greatly enhanced at high I. Leaf disc treatment at 35 in the dark did not change quantum yield or Pn. When in addition to 35 the leaves were subjected to high I (TS + IS) or to high I and dehydration (TS + IS + WS), then a substantial decrease was observed in the quantum yield (66 and 77 % of the values in Controls, respectively) and in (31 and 56 %, respectively).