Enhanced leaf elongation rates of wheat at elevated COâ‚‚ : is it related to carbon and nitrogen dynamics within the growing leaf blade?

This paper addresses the question of whether leaf elongation rates (LER) of monocots is controlled at high atmospheric COâ‚‚ by nitrogen (N) and/or carbohydrate concentrations in the zones of cell division and expansion in the basal meristem of growing leaf blades. Wheat (Triticum aestivum L. cv. Hartog) was grown at high N supplies at either 360 or 700 μmol COâ‚‚ molâ»ÂÃ"šÃ‚¹ in artificially illuminated growth chambers for 30 days prior to final harvest to determine growth parameters and chemical composition of leaf blades. We particularly focused on the spatial distribution of carbon (C), N and carbohydrate concentrations along the expanding leaf blade. Elevated COâ‚‚ accelerated LER of expanding blade (sixth leaf blade) by 32% and this factor contributed to increase in total leaf area (18%) and shoots mass (36%). N concentrations in the expanding and last fully expanded leaf blade (LFEL) were reduced by 18% and 33%, respectively, at elevated COâ‚‚ but soluble carbohydrate concentrations were significantly increased in the expanded leaves only. N concentrations were highest in the zones of cell division and expansion of the elongating blade but were unaffected by high COâ‚‚ and reductions in N concentration only appeared in the cell maturing zone where division and expansion had ceased. The concentration of soluble carbohydrates was greater in the cell division and expansion than in maturation zones but was unaffected by high COâ‚‚. C concentration was also little affected by elevated COâ‚‚ in any zone of the blade. We conclude that greater availability of soluble carbohydrates for export from the expanded to expanding blades is the driving force for accelerated LER at elevated COâ‚‚. It is unlikely that N concentrations limited leaf growth at high COâ‚‚ because its concentration was unaffected by COâ‚‚ in the zones of cell division and expansion that are most sensitive to N supply.