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Does Elevated CO2 Accelerate Barley Flag Leaf Senescence to Help Increase Grain Yield?
Reference
Fangmeier, A., Chrost, B., Hogy, P. and Krupinska, K.  2000.  CO2 enrichment enhances flag leaf senescence in barley due to greater grain nitrogen sink capacity.  Environmental and Experimental Botany 44: 151-164.

What was done
Barley (Hordeum vulgare L. cv. Alexis) plants were grown in containers placed within open-top chambers receiving atmospheric CO2 concentrations of 360 and 650 ppm to study the effects of elevated CO2 on yield production and senescence in this important agricultural grain crop.  In addition, plants were subjected to a high and low nitrogen fertilization regime to see if nitrogen availability interacted with elevated CO2 to affect any of these processes.

What was learned
Elevated CO2 stimulated barley growth and biomass production in both nitrogen regimes.  In fact, it increased total grain yield by 48 and 31% in the low and high nitrogen regimes, respectively.  Thus, elevated CO2 had the greatest relative impact on yield when plants were grown under the less-than-optimal low nitrogen regime.

Senescence, which is regarded as a highly effective process that salvages nutrients from older tissues to facilitate the growth of newer ones, was enhanced by elevated CO2.  Leaf chlorophyll concentration, for example, dropped to 50% of its maximum value in CO2-enriched plants four days earlier than in plants grown at ambient CO2.  Similar results were also observed for protein remobilization out of CO2-enriched barley leaves.

What it means
As the atmospheric CO2 concentration increases, barley plants will likely exhibit increased photosynthetic rates, as well as increased biomass and yield production, regardless of soil nitrogen content.  Although the greatest absolute yield increases will likely be observed under nitrogen-rich soil conditions, the greatest relative CO2-induced yield increases will likely occur on nitrogen-poor soils.  In either case, meeting the increased nitrogen demands of the greater numbers of individual grains produced in CO2-enriched air will likely be facilitated by enhancing the process of senescence in barley leaves, so that nitrogen can be mobilized away from leaves and into developing grains earlier in the season.  Thus, greater barley grain yields can be expected under future atmospheres containing greater concentrations of CO2.


Reviewed 27 February 2002