Diffuse photon flux density of photosynthetically active radiation (PAR) was measured throughout the season in peach trees [Prunus persica (L.) Batsch. cv. Harken] trained to an open center. Penetration of PAR generally decreased as shoot extension continued through the season. PAR was greater at the tree periphery and center than midway between the 2 points. PAR also decreased from the upper levels to the lower levels of the tree canopy. Specific leaf weight (SLW) at all positions increased from early June until August. SLW generally followed the same pattern as PAR, with lowest SLW developing midway between the tree periphery and center. Net photosynthesis (Pn) was greatest for peripheral leaves, lowest for leaves midway into the tree, and intermediate for leaves from the tree center. Pn and SLW were linearly correlated. Leaves developing at different distances from the tree center had similar stomatal resistances. There was no consistent influence of canopy position on chlorophyll content, but interior leaves tended to have greater chlorophyll content than peripheral leaves.
Received for publication December 8, 1982. New Jersey Agricultural Experiment Station, Publication No. D-12146-13-82, supported by State funds. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.