Barley Growth and Its Underlying Components are Affected by Elevated CO2 and Salt Concentration

Abstract

The future environment will exhibit increases in soil salt concentrations and atmospheric CO2. In general, plant growth is inhibited by salt stress and stimulated by elevated CO2. This study investigated whether elevated CO2 could improve plant growth under salt stress and the mechanisms involved. We measured functional and morphological components of growth in barley (cv. Iranis) subjected to 0, 80, 160, or 240 mM NaCl and grown at either 350 (ambient) or 700 (elevated) μmol mol−1 CO2. Under nonsaline conditions, elevated CO2 stimulated growth by increasing the relative growth rate (RGR). Maximum CO2 stimulation was observed within the first 10 days of development, before the start of the salt treatment. Afterwards, salt stress caused reductions in biomass production and RGR by decreasing the photosynthetic rate and increasing the respiration rate; this resulted in a reduced net assimilation rate (functional component). In addition, salt stress caused nutritional imbalances, which reduced the leaf expansion capacity, and changed the root-to-shoot ratio. This resulted in reductions in the specific leaf area and leaf weight ratio (morphological components). However, the functional component became more relevant with increasing salt stress. Under elevated CO2 conditions, salt stress inhibited growth less than that observed at ambient CO2. This occurred because (1) more dry biomass was synthesized for a given leaf area due to higher photosynthetic rates, and (2) greater leaf area and root biomass were maintained for photosynthesis and water and mineral uptake, respectively.