Interaction between CO₂enrichment and salinity stress in the C₄non‐halophyteAndropogon glomeratus(Walter) BSP

Increasing atmospheric CO 2 may result in alleviation of salinity stress in salt‐sensitive plants. In order to assess the effect of enriched CO 2 on salinity stress in Andropogon glomeratus , a C 4 non‐halophyte found in the higher regions of salt marshes, plants were grown at 350, 500, and 650 cm 3 m −3 CO 2 with 0 or 100 mol m −3 NaCl watering treatments. Increases in leaf area and biomass with increasing CO 2 were measured in salt‐stressed plants, while decreases in these same parameters were measured in non‐salt‐stressed plants. Tillering increased substantially with increasing CO 2 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 CO 2 in salt‐stressed plants, although short‐term increases probably occurred. Stomatal conductance decreased with increasing CO 2 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 CO 2 treatments in the salt‐stressed plants. Decreases in photosynthesis in salt‐stressed plants occurred primarily as a result of decreased internal (non‐stomatal) conductance.