Reference
Perez-Lopez, U., Robredo, A., Lacuesta, M., Mena-Petite, A. and Munoz-Rueda, A. 2009. The impact of salt stress on the water status of barley plants is partially mitigated by elevated CO2. Environmental and Experimental Botany 66: 463-470.
Background
The authors write that "salinity is one of the major abiotic factors limiting global agricultural productivity, rendering an estimated one-third of the world's irrigated land unsuitable for crop production (Frommer et al., 1999)."
What was done
Two different barley (Hordeum vulgare L.) cultivars (Alpha and Iranis) were grown from seed in a 3:1 mixture of perlite:vermiculite within controlled-environment chambers that were maintained at atmospheric CO2 concentrations of either 350 or 700 ppm for a period of four weeks, while being watered and fertilized every second day with a solution of one of four different salinities (0, 80, 160 or 240 mM NaCl), while measurements were made of relative water content, water potential and its components, transpiration rate, hydraulic conductance, and water use efficiency, computed as plant dry weight produced per unit of water transpired.
What was learned
It was determined, in the words of Perez-Lopez et al., that "elevated CO2 improves barley water relations under saline conditions because elevated CO2 permits a greater osmotic adjustment, most likely due to a greater carbon supply from increased photosynthesis, and a lower passive dehydration due to reductions in stomatal conductance and hydraulic conductance." More specifically, they report that by the end of their study the water use efficiency of salt-stressed plants grown in the elevated CO2 treatment was 61% greater in Alpha and 43% greater in Iranis compared to the water use efficiency of plants grown in the ambient CO2 treatment.
What it means
The five researchers "propose that elevated CO2 will mitigate the negative impact of salinity on barley growth and will enable plants to remain turgid and functional for a longer period and for a higher salt concentration," noting that "these facts open the possibility of a future successful development of this species in saline areas in which nowadays growth is not possible." This finding has enormous implications, in light of the fact that Frommer et al. (1999) have estimated that approximately one-third of the world's irrigated land is currently unsuitable for crop production because of its high salinity.
Reference
Frommer, W.B., Ludewig, U. and Rentsch, D. 1999. Taking transgenic plants with a pinch of salt. Science 285: 1222-1223.