Interaction between CO2 enrichment and salinity stress in the C4 non-halophyte Andropogon glomeratus (Walter) BSP

Abstract Increasing atmospheric CO₂ may result in alleviation of salinity stress in salt-sensitive plants. In order to assess the effect of enriched CO₂ on salinity stress in Andropogon glomeratus, a C₄ non-halophyte found in the higher regions of salt marshes, plants were grown at 350, 500, and 650 cm³ m^?3 CO₂ with 0 or 100 mol m^?3 NaCl watering treatments. Increases in leaf area and biomass with increasing CO₂ were measured in salt-stressed plants, while decreases in these same parameters were measured in non-salt-stressed plants. Tillering increased substantially with increasing CO₂ in salt-stressed plants, resulting in the increased biomass. Six weeks following initiation of treatments, there was no difference in photosynthesis on a leaf area basis with increasing CO₂ in salt-stressed plants, although short-term increases probably occurred. Stomatal conductance decreased with increasing CO₂ in salt-stressed plants, resulting in higher water-use efficiency, and may have improved the diurnal water status of the plants. Concentrations of Na⁺ and Cl^? were higher in salt stressed-plants while the converse was found for K ⁺. There were no differences in leaf ion content between CO₂ treatments in the salt-stressed plants. Decreases in photosynthesis in salt-stressed plants occurred primarily as a result of decreased internal (non-stomatal) conductance.