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Crop Science Abstract -

Stomatal Closure vs. Osmotic Adjustment: a Comparison of Stress Response1


This article in CS

  1. Vol. 27 No. 3, p. 539-543
    Received: Aug 7, 1986

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  1. Keith J. McCree and
  2. Steven G. Richardson2



A common response to water stress is stomatal closure, which reduces fluxes of both CO2 and water vapor. Alternatively, stomates may remain open while turgor is maintained through osmotic adjustment. The latter response should result in a greater C gain. To test this, daily whole plant C balances and water losses of cowpea plants (Vigna unguiculata L. Walp.) were compared with those of sugarbeet plants (Beta vulgaris L.) of equal leaf area. Under frequent irrigation and controlled environment conditions typical of warm, humid, sunny days, C gain and water-loss rates were almost identical in the two species. When irrigation was withheld, the sugarbeet plants adjusted osmotically by 0.8 kJ kg−1 (0.8 MPa, 8 bars) and reached a daytime minimum leaf water potential of −2.6 kJ kg−1 at the time of re-irrigation, while the cowpea plants adjusted by half as much but maintained a higher water potential (−1.2 kJ kg−1) by stomatal closure. At any given water potential, water-loss rates were much smaller in the cowpea plants, but on any given day, the rates were very similar in the two species. This was because the water potential fell much more rapidly in the sugarbeet plants. The C gain rates were also similar. The comparison of these two species showed little or no C gain advantage of osmotic adjustment over stomatal closure.

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