Carbon and nitrogen allocation and partitioning in traditional and modern wheat genotypes under pre-industrial and future CO₂ conditions.

The results of a simultaneous (13)C and (15)N labelling experiment with two different durum wheat cultivars, Blanqueta (a traditional wheat) and Sula (modern), are presented. Plants were grown from the seedling stage in three fully controllable plant growth chambers for one growing season and at three different CO₂ levels (i.e. 260, 400 and 700 ppm). Short-term isotopic labelling (ca. 3 days) was performed at the anthesis stage using (13)CO₂ supplied with the chamber air and (15)NH₄₋(15)NO₃ applied with the nutrient solution, thereby making it possible to track the allocation and partitioning of (13)C and (15) N in the different plant organs. We found that photosynthesis was up-regulated at pre-industrial CO₂ levels, whereas down-regulation occurred under future CO₂ conditions. (13)C labelling revealed that at pre-industrial CO₂ carbon investment by plants was higher in shoots, whereas at future CO₂ levels more C was invested in roots. Furthermore, the modern genotype invested more C in spikes than did the traditional genotype, which in turn invested more in non-reproductive shoot tissue. (15)N labelling revealed that the modern genotype was better adapted to assimilating N at higher CO₂ levels, whereas the traditional genotype was able to assimilate N more efficiently at lower CO₂ levels.