Estimating the excess investment in ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of spring wheat grown under elevated CO2

摘要

Wheat (Triticum aestivum) cv. Minaret was grown under CO2 partial pressures of 36 (ambient) or 70 Pa (elevated) and given 4.6 (low) or 12.5 mM N. Responses of photosynthesis to varying CO2 partial pressures were fitted to estimate the maximal carboxylation rate and the non-photorespiratory respiration rate in flag and preceding leaves. The maximal carboxylation rate was proportional to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content, and the light-saturated photosynthetic rate at70 Pa CO2 was proportional to the thylakoid ATP-synthase content. Potential photosynthetic rates at 70 Pa CO2 were calculated and compared with the observed values to estimate excess investment in Rubisco. The excess was greater in leaves grown with highN application than in those grown with low N application and declined as the leaves senesced. The fraction of Rubisco that was estimated to be in excess was strongly dependent on leaf N content, increasing from approximately 5% in leaves with 1 g N m-2to approximately 40% in leaves with 2 g N m-2. Growth at elevated CO2 usually decreased the excess somewhat but only as a consequence of a general reduction in leaf N, since relationships between the amount of components and N content were unaffected byCO2. It was concluded that there is scope for improving the N-use efficiency of C3 crop species under elevated CO2 conditions.