Intraspecific variation in growth and yield response to elevated CO2 in wheat depends on the differences of leaf mass per unit area

In order to investigate the underlying physiological mechanism of intraspecific variation in plant growth and yield response to elevated CO2 concentration [CO2], seven cultivars of spring wheat (Triticum aestivum L.) were grown at either ambient [CO2] (similar to 384 mu mol mol(-1)) or elevated [CO2] (700 mu mol mol(-1)) in temperature controlled glasshouses. Grain yield increased under elevated[CO2] by an average of 38% across all seven cultivars, and this was correlated with increases in both spike number (productive tillers) (r = 0.868) and aboveground biomass (r = 0.942). Across all the cultivars, flag leaf photosynthesis rate (A) increased by an average of 57% at elevated [CO2]. The response of A to elevated [CO2] ranged from 31% (in cv. H45) to 75% (in cv. Silverstar). Only H45 showed A acclimation to elevated [CO2], which was characterised by lower maximum Rubisco carboxylation efficiency, maximum electron transport rate and leaf N concentration. Leaf level traits responsible for plant growth, such as leaf mass per unit area (LMA), carbon (C), N content on an area basis ([N](LA)) and the C : N increased at elevated [CO2]. LMA stimulation ranged from 0% to 85% and was clearly associated with increased [N](LA). Both of these traits were positively correlated with grain yield, suggesting that differences in LMA play an important role in determining the grain yield response to elevated [CO2]. Thus increased LMA can be used as a new trait to select cultivars for a future [CO2]-rich atmosphere.