Annals of Botany 79: 191-196, 1997
© 1997 Annals of Botany Company
Differentiating Day from Night Effects of High Ambient [CO2] on the Gas Exchange and Growth of Xanthium strumarium L. Exposed to Salinity Stress
Department of Botany, Hebrew University of Jerusalem, Jerusalem, 91904, Israel The Jacob Blaustein Institute for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion, 84990, Israel
March 25, 1996 ; September 2, 1996
Sodium chloride, at a concentration of 88 mol m-3in half strength Hoagland nutrient solution, increased dry weight per unit area ofXanthium strumarium L. leaves by 19%, and chlorophyll by 45% compared to plants grown without added NaCl at ambient (350 µmol mol-1) CO2concentration. Photosynthesis, per unit leaf area, was almost unaffected. Even so, over a 4-week period, growth (dry weight increment) was reduced in the salt treatment by 50%. This could be ascribed to a large reduction in leaf area (>60%) and to an approx. 20% increase in the rate of dark respiration (Rd).
Raising ambient [CO2] from zero to 2000 µmol mol-1decreased Rd in both control and salinized plants (by 20% at 1000, and by 50% at 2000 µmol mol-1CO2concentration) compared to Rd in the absence of ambient CO2. High night-time [CO2] had no significant effect on growth of non-salinized plants, irrespective of day-time ambient [CO2]. Growth reduction caused by salt was reduced from 51% in plants grown in 350 µmol mol-1throughout the day, to 31% in those grown continuously in 900 µmol mol-1[CO2].
The effect of [CO2] at night on salinized plants depended on the daytime CO2concentration. Under 350 µmol mol-1day-time [CO2], 900 µmol mol-1at night reduced growth over a 4-week period by 9% (P <0.05) and 1700 µmol mol-1reduced it by 14% (P <0.01). However, under 900 µmol mol-1day-time [CO2], 900vs . 350 µmol mol-1[CO2] at night increased growth by 17% (P <0.01).
It is concluded that there is both a functional and an otiose (functionless) component to Rd, which is increased by salt. Under conditions of low photosynthesis (such as here, in the low day-time [CO2] regime) the otiose component is small and high night-time [CO2] partly suppresses functional Rd, thereby reducing salt tolerance. In plants growing under conditions which stimulate photosynthesis (e.g. with increased daytime [CO2]), elevated [CO2] at night suppresses mainly the otiose component of respiration, thus increasing growth. Consequently, in regions of adequate water and sunlight, the predicted further elevation of the world atmospheric [CO2] may increase plant salinity tolerance.
Xanthium strumarium ; respiration; photosynthesis; salt stress; sodium chloride; carbon dioxide; atmosphere
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