Annals of Botany · 1997 · 35 citations · 31 references
Life SciencesPlant BiologyPlant SciencesPhotosynthesisPlant EcophysiologyPlant PhysiologyEnvironmental Responses Of PhotosynthesisPlant Gas ExchangePlant RespirationSalinity PhysiologySalinity Stress PhysiologySalt Stress PhysiologyPhotosynthesis Under SalinityPhotosynthetic Performance Under SalinityPhotosynthetic Responses To SalinityPlant Response To SalinityRespiratory Gas ExchangeSalinity Effects On PhotosynthesisSalinity ToleranceSalt Tolerance
Sodium chloride, at a concentration of 88 mol m −3 in half strength Hoagland nutrient solution, increased dry weight per unit area of Xanthium strumarium L. leaves by 19%, and chlorophyll by 45% compared to plants grown without added NaCl at ambient (350 μmol mol −1 ) CO 2 concentration. 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 [CO 2 ] from zero to 2000 μmol mol −1 decreased Rd in both control and salinized plants (by 20% at 1000, and by 50% at 2000 μmol mol −1 CO 2 concentration) compared to Rd in the absence of ambient CO 2 . High night-time [CO 2 ] had no significant effect on growth of non-salinized plants, irrespective of day-time ambient [CO 2 ]. Growth reduction caused by salt was reduced from 51% in plants grown in 350 μmol mol −1 throughout the day, to 31% in those grown continuously in 900 μmol mol −1 [CO 2 ]. The effect of [CO 2 ] at night on salinized plants depended on the daytime CO 2 concentration. Under 350 μmol mol −1 day-time [CO 2 ], 900 μmol mol −1 at night reduced growth over a 4-week period by 9% ( P <0.05) and 1700 μmol mol −1 reduced it by 14% ( P <0.01). However, under 900 μmol mol −1 day-time [CO 2 ], 900 vs . 350 μmol mol −1 [CO 2 ] 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 [CO 2 ] regime) the otiose component is small and high night-time [CO 2 ] partly suppresses functional Rd, thereby reducing salt tolerance. In plants growing under conditions which stimulate photosynthesis (e.g. with increased daytime [CO 2 ]), elevated [CO 2 ] 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 [CO 2 ] may increase plant salinity tolerance.
31