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This article in CS

  1. Vol. 10 No. 1, p. 42-45
    Received: June 30, 1969

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Varietal Differences in Net Photosynthesis of Soybean Leaves1

  1. Gary M. Dornhoff and
  2. R. M. Shibles2



Leaf net CO2 exchange of 20 varieties of soybeans (Glycine max (L.) Merr.) was measured by infrared gas analysis. The varieties differed significantly in net photosynthesis at 100, 200, 300, and 400 ppm CO2. Both stomatal resistance and mesophyll resistance to diffusion of CO2 were different among genotypes. No genotypic differences were found in CO2 evolution into CO2-free air in light, or in CO2 compensation concentration. Density-thickness (leaf weight to leaf area ratio), on both dry- and fresh-weight bases, was highly correlated with net photosynthesis. The evidence suggests that varietal differences in net photosynthesis were mainly a result of differences in diffusive resistances.

Net photosynthesis of most varieties began to increase around Aug. 4, at the approximate beginning of seed filling. A linear trend in increasing leaf density-thickness occurred from beginning of testing. The increase in net photosynthesis is postulated a result of (a) decreased CO2 diffusion resistance within the leaf, and/or (b) increased demandfo r photosynthate for seed formation.

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