Effect of Leaf Age and Position on Photosynthesis and Stomatal Conductance of Forage Grasses1

Abstract

AbstractInformation on photosynthesis and stomatal conductance of different position leaves is needed to determine which leaf to sample for comparing rates of different grass species and genotypes. Photosynthesis and stomatal conductance were measured on the top three or four leaves on several dates after leaf collar formation on field‐grown accessions of pubescent wheatgrass [Agropyron intermedium var. trichophorum (Link) Halac.], crested wheatgrass [A. desertorum (Fisch. ex Link) Schult.], and reed canarygrass (Phalaris arundinacea L.). The study was conducted during 1976 and 1977 at Mandan, ND. Stomatal conductance was a primary factor affecting photosynthesis throughout the growing period. Leaf‐age effects were difficult to evaluate, but the data suggested a negligible effect of leaf age on photosynthesis for the three species studied. Leaf‐position effects were more evident for pubescent and crested wheatgrass than for reed canarygrass. There was no interaction between leaf position and genotypes within species. The uppermost leaves of each species studied had higher rates of photosynthesis at a given conductance when compared with lower position leaves.The study showed that, to compare genotypes within a species, relative photosynthetic rates of single leaves, can be determined from different leaf positions and from the time of leaf collar formation until leaf senescence, provided that these comparisons are made within each leaf position.