A new method of applying a controlled soil water stress, and its effect on the growth of cotton and soybean seedlings at ambient and elevated carbon dioxide
2012
Bunce, James A. | Nasyrov, Muhtor
While numerous studies have shown that elevated CO₂ can delay soil water depletion by causing partial stomatal closure, few studies have compared responses of plant growth to the same soil water deficits imposed at ambient and elevated CO₂. We applied a vacuum to ceramic cups in pots filled with soil to reduce the soil water matric potential to −0.10MPa. This system resulted in uniform soil water content throughout the pot, and was used to maintain a constant mild stress for seven days. In cotton, the soil water stress treatment reduced stomatal conductance at both 380 and 560μmolmol⁻¹ CO₂, but the reduction was relatively smaller at the higher CO₂. No reduction of photosynthesis measured under the daytime growth conditions occurred at elevated CO₂ in stressed cotton plants, while photosynthesis was reduced by the stress in the lower CO₂ treatment. The soil water stress treatment reduced the leaf area and biomass of cotton at the lower, but not at the higher CO₂. In soybean, the soil water stress treatment reduced stomatal conductance, photosynthesis and growth at both CO₂ levels, but the effect of water stress was not less at elevated than ambient CO₂. In neither species nor CO₂ level did the soil water stress treatment cause a detectable change in daytime leaf water potential. In both species, the stomatal closure with the soil water stress may have resulted from the lower soil to leaf hydraulic conductivity. The failure of high CO₂ to protect soybean growth from the soil water stress might be related to the lower hydraulic conductivity of stressed soybeans grown at elevated compared with ambient CO₂.
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