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This article in CS

  1. Vol. 22 No. 4, p. 886-890
     
    Received: Aug 5, 1981


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doi:10.2135/cropsci1982.0011183X002200040044x

Cultivar Differences in Canopy Apparent Photosynthesis and Their Relationship to Seed Yield in Soybeans1

  1. R. Wells,
  2. L. L. Schulze,
  3. D. A. Ashley,
  4. H. R. Boerma and
  5. R. H. Brown2

Abstract

Abstract

Differences in leaf photosynthesis among soybean [Glycine max (L.) Merr.] genotypes have not been shown to be correlated with seed yield, probably because leaves selected for measurement have not been representative of the soybean canopy. In order to obtain a measure more representative of photosynthesis by plant communities and to explore the relationship of canopy apparent photosynthesis (CAP) to seed yield, field experiments were conducted during 2 years. Four soybean cultivars in each of four Maturity Groups (V through VIII) were grown in field plots in 1975 and two of each Maturity Group were grown in 1976. Measurements of CAP were made throughout the reproductive period by placing a large plastic covered chamber over a square meter segment of the canopy and measuring CO2Differences in leaf photosynthesis among soybean [Glycine max (L.) Merr.] genotypes have not been shown to be correlated with seed yield, probably because leaves selected for measurement have not been representative of the soybean canopy. In order to obtain a measure more representative of photosynthesis by plant communities and to explore the relationship of canopy apparent photosynthesis (CAP) to seed yield, field experiments were conducted during 2 years. Four soybean cultivars in each of four Maturity Groups (V through VIII) were grown in field plots in 1975 and two of each Maturity Group were grown in 1976. Measurements of CAP were made throughout the reproductive period by placing a large plastic covered chamber over a square meter segment of the canopy and measuring CO2 depletion during a 1 to 2 min period. Measurements were made near noon when solar radiation was above 0.9 Ly/min.

Maximum values of CAP were 4 to 6 g CO2m-2hr-1 during the early reproductive stages and decreased with age throughout pod filling. The decrease was most rapid for Maturity Group V and slowest for Group VIII. Dates when CAP dropped to zero were mid-September for the Group V cultivars and mid-October for Group VIII. Differences in CAP among cultivars occurred during seed development for all Maturity Groups. These differences could not be attributed to leaf area index or light interception since differences in CAP occurred while light interception was above 97%. Seed yield also differed among cultivars within Maturity Groups, the range in yield being from about 2,000 to 3,600 kg/ha in both years. Correlation coefficients for the association between yield and CAP measured during seed development were significant and ranged from 0.43 to 0.62. An integral of the CAP measurements from the full-pod stage of development (R-4) to maturity was correlated with yield with a coefficient of 0.66 in 1975 and 0.59 in 1976. Data from these experiments indicate that yield differences among cultivars are partially accounted for by differences in photosynthetic capacity of the plant canopy during seed development.

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