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Effects of Elevated CO2 on Barley Growing Under Iron-Limited Conditions
Haase, S., Rothe, A., Kania, A., Wasaki, J., Romheld, V., Engels, C., Kandeler, E. and Neumann, G. 2008. Responses to iron limitation in Hordeum vulgare L. as affected by the atmospheric CO2 concentration. Journal of Environmental Quality 37: 1254-1262.

What was done
The authors grew barley (Hordeum vulgare L. cv. Europa) plants from seed for four weeks -- both hydroponically in nutrient solution having adequate or less-than-adequate iron (Fe) concentrations (+Fe and -Fe, respectively), as well as in rhizobox microcosms filled with soil under the same two conditions of iron availability -- in controlled-environment chambers maintained at atmospheric CO2 concentrations of either 400 or 800 ppm, while they measured a number of pertinent plant physiological parameters.

What was learned
Haase et al. report that the elevated atmospheric CO2 treatments stimulated biomass production in both Fe-sufficient and Fe-deficient barley plants, in both hydroponics and soil culture. In addition, they say there were three different CO2-induced modifications in plant activity: "(i) increased internal Fe use efficiency, (ii) stimulation of root growth, and (iii) increased root exudation of Fe-mobilizing phytosiderophores in the sub-apical root zones."

What it means
Since phytosiderophores act as metal chelators that mobilize sparingly soluble inorganic forms of iron and zinc and make them more readily available to plants, the researchers suggest that atmospheric CO2 enrichment increases the competitiveness of plants such as barley with rhizosphere microorganisms in their quest for these often difficult-to-obtain trace elements, which help to explain the strong growth response of barley to atmospheric CO2 enrichment, even when iron availability is low.

Reviewed 23 July 2008