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Influence of Elevated CO2 on Rubisco Content in Leaves of Wheat
Theobald, J.C., Mitchell, R.A.C., Parry, M.A.J. and Lawlor, D.W.  1998.  Estimating the excess investment in ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of spring wheat grown under elevated CO2Plant Physiology 118: 945-955.

What was done
In three separate experiments, the authors grew spring wheat in growth chambers receiving 360 or 700 ppm atmospheric CO2 and low or high nitrogen supply, to study how these parameters influence photosynthetic acclimation.  Specifically, they studied how nitrogen availability influences the amount of rubisco required to maintain observed rates of photosynthesis at 700 ppm CO2.

What was learned
The authors determined that growth at elevated CO2 reduces the amount of rubisco required to maintain enhanced rates of photosynthesis, and that this phenomenon occurs as an indirect consequence of elevated CO2 reducing leaf nitrogen content, and not as a direct effect of CO2 on leaf photosynthetic components.  Furthermore, the amount of excess rubisco declined with decreasing nitrogen supply regardless of CO2 concentration.

What it means
As the concentration of CO2 in the air rises, photosynthetic acclimation, which effectively reduces the amount of rubisco in leaves (which is often present in excess amounts), may occur to a greater extent in plants growing at high soil nitrogen, rather than at low soil nitrogen, as greater amounts of rubisco are generally present under higher soil nitrogen regimes.  In either case, the mobilization of nitrogen from excess rubisco can supply needed nitrogen to plant sink tissues to allow for their continued growth and development.  In all cases, therefore, atmospheric CO2 enrichment enhances the use efficiency of nitrogen and enables plants to grow more productively in soils regardless of their fertility.

Reviewed 1 May 1999