Elevated CO₂ Improves the Growth of Wheat Under Salinity

Abstract

Wheat plants (Triticum aestivum cv. Matong and T. durum cv. Modoc) were grown at ambient and elevated CO₂ (350 cm³ m^-3 above ambient) in soil with or without 150 mol m^-3 NaCl for 6 weeks. The increase in dry matter, leaf area and tillering under high CO₂ was relatively greater under saline than non-saline conditions for both cultivars. Tillering was the primary component of growth affected by both salinity and high CO₂. Salinity greatly reduced tillering and high CO₂ partly reversed the effects of salinity. High CO₂ increased dry matter accumulation of the salt-sensitive Modoc to a greater extent (+104%) than that of the more salt-tolerant Matong (+73%) in the salt treatment. Transpiration rates were greatly reduced by salinity for both cultivars. Under high CO₂, increased leaf areas compensated for reduced transpiration rates per unit leaf area (i.e. greater stomatal closure), and total transpiration was little affected by CO₂ level within each treatment. The more salt-tolerant Matong showed greater stomatal closure and higher transpiration efficiencies than the salt-sensitive Modoc under salinity. High CO₂ reduced transpiration rate (per unit dry weight) by 40 to 50%, but did not significantly change the rate of sodium accumulation (per unit dry weight), indicating that salt uptake was largely independent of water uptake, and that high CO₂ did not increase growth by reducing the salt load. Our results suggest that high CO₂ increased growth by stimulating the development of tiller buds that would otherwise have been inhibited.