Leaf age, leaf blade portion and light intensity as determinants of leaf photosynthesis in Panicum maximum Jacq.

The objective in this research was to identify photosynthetic responses of three leaf age groups measured in three portions of the leaf blade of two morphologically contrasting genotypes of P anicum maximum . Photosynthetic rate ( PR ) varied across leaf age groups and among leaf portions. Highest PR (20.6 μmol CO 2 m −2 s −1 ) was recorded on the youngest fully expanded leaf, followed by the oldest green leaf and the expanding leaf. The middle and apical portions of the leaf had, on average, the highest PR (24.2 and 26.3 μmol CO 2 m −2 s −1 , respectively). In both ‘ M assai’ and ‘T obiatã’ cultivars the photosynthetic response was dependent upon leaf age groups and portions of the blade, with highest rates measured on the middle portion of the youngest fully expanded leaf. The P. maximum had similar parameters for the light response curve suggesting similar photosynthetic light response to light intensity across genotypes.