Background
The authors write that "soil salinization is an important growth limiting factor for most plants," citing the United Nations' Food and Agriculture Organization (FAO, 2007), while noting that "around 20% of the irrigated land and one third of the world's arable soil are affected by a progressive salinization." And against this backdrop, they indicate that "barley is one of the most extensively cultivated crops worldwide" but that "salt stress reduces its productivity."

What was done
Perez-Lopez et al. analyzed "the effect of salinity on nitrogen acquisition, distribution and assimilation, the consequences of these effects on growth in barley (Hordeum vulgare L., cv. Iranis), and the possible effects on these processes provoked by elevated CO2 levels." This they did in controlled environment chambers maintained at either ambient (350 ppm) or elevated (700 ppm) CO2 concentrations, where - from the time of sowing six barley seeds in each of several 2.5-liter pots containing a 3:1 mix of perlite/vermiculite - they watered the plants with 250 ml of Hoagland's solution containing either 0, 80, 160 or 240 mM concentrations of NaCl every two days until the end of the 28-day study.

What was learned
The six Spanish scientists report that "under ambient CO2 conditions, 80, 160 and 240 mM NaCl reduced the total plant biomass by 12%, 30% and 44%, respectively," while "growth at elevated CO2 levels led to 24%, 20% and 33% higher total biomass than under ambient CO2 levels for 80, 160 and 240 mM NaCl, respectively."

What it means
Because of the fact that "the relative stimulation of total plant biomass in response to elevated CO2 levels was higher in salt-stressed plants than in non-stressed ones," Perez-Lopez et al. state that "barley plants subjected to elevated CO2 levels will likely overcome mild saline conditions." And with the need to produce approximately twice the amount of food that is produced now to adequately feed the projected human population of the planet by mid-century (Running, 2012), we are going to need all the help we can get; and the boost in barley productivity (as well as that of many other crop plants) provided by mankind's CO2 enrichment of the atmosphere will be crucial if we are to be successful in this endeavor.

References
FAO, 2007. Global Network on Integrated Soil Management for Sustainable Use of Salt-affected Soils. http:/www.fao.org/nr/land/soils/.

Running, S.W. 2012. A measurable planetary boundary for the biosphere. Science 337: 1458-1459.