Growth Analysis of Maize Hybrids Differing in Photosynthetic Capability1

Abstract There is, theoretically, a close association between leaf photosynthesis and dry matter production. However, many factors affect plant productivity and photosynthesis under field conditions which are not measured with leaf photosynthesis in the laboratory. Studies were undertaken to determine if there are patterns of leaf area development or dry matter accumulation in maize (Zea mays L.) plants that may interfere with a leaf‐photosynthesis, plant‐productivity relationship. Six experimental maize hybrids were selected for detailed growth analysis during vegetative development. Three of these hybrids had previously exhibited higher CO2 exchange rates (CER) and three had exhibited lower CER. Plants were sown in the field in early May and early June to obtain densities of 5.3 plants/m2 during the 1978 and 1979 growing seasons. The soil was a Clarion (Typic Hapludoll, fine‐loamy, mixed mesic) soil. Leaf CER of excised blades, leaf blade area on main culms and tillers, and dry weight of main culms and tillers were measured weekly through 6 weeks of growth. The hybrids maintained the CER status for which they were selected during all growth periods. High‐CER hybrids tillered more profusely than did low‐CER hybrids. Overall leaf area was greater in high‐CER hybrids, primarily due to greater tillering. Dry weight of main culms and tillers among hybrids generally followed leaf area distribution. Dry weight accumulation patterns between main culm and tillers during late vegetative development suggested that high‐CER hybrids exported “excess” main culm assimilates to nonproductive tillers or belowground sinks. This phenomenon, if real, would affect any yield advantage attributable to high CER capability.