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This article in CS

  1. Vol. 17 No. 5, p. 713-716
     
    Received: Jan 3, 1977


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doi:10.2135/cropsci1977.0011183X001700050010x

Effect of Water Stress on Carbon Assimilation and Distribution in Soybean Plants at Different Stages of Development1

  1. J. E. Silvius,
  2. R. R. Johnson and
  3. D. B. Peters2

Abstract

Abstract

The effects of water stress on carbon dioxide (CO2) exchange rates (CER) and assimilate distribution were studied in chamber-grown soybean plants (Glycine max (L.) Merr., ‘Fiskeby’) in the vegetative, flowering, and pod-filling stages of development. When water was withheld, the decrease in CER was correlated with the increase in stomatal resistance at leaf water potentials as low as −21 bars. Under the above conditions, CER and stomatal resistance recovered to predesiccation levels within 24 hours after rewatering. When leaf water potentials were allowed to drop below −21 bars, recovery of CER lagged behind the return of stomatal resistance to predesiccation levels, suggesting that additional factors may be involved. Whole plants were exposed to labeled CO2 at the three different stages of development and the percent distribution of 14C was determined. At leaf water potentials of −15 to −20 bars, plants displayed alterations in 14C distribution among plant parts corresponding to alterations in dry weight distribution. Compared to well-watered plants, relatively more 14C was found in the roots of water-stressed plants before the pod-filling stage. Less 14C was retained in the leaf blades of these plants, but this response was reversed during pod-filling. Reduction in 14C in nodules was associated with water stress at all growth stages. Percentage of radioactivity increased in leaves and reproductive structures of plants rewatered and exposed to 14CO2 following return of CER to predesiccation levels. Our results suggest that drought decreased CER and altered assimilate distribution, producing growth modifications that favor efficient use of the limited supply of fixed carbon.

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