Response of matter production of two winter wheat genotypes with differing nitrogen efficiency to di-atmospheric CO₂ concentration and nitrogen supply

Atmospheric carbon dioxide (CO₂) level continues to rise at an unprecedented rate and is expected to exceed 750 μmol·mol^-1 by the end of the 21st century. Increasing atmospheric CO₂ concentration has been associated to changes in global environment. The effect of elevated atmospheric CO₂, as driven by global environmental change, on agricultural production remains unclear. To further clarify this effect, leaf area, plant height, biomass and yield of two winter wheat varieties (the high N efficiency “Xiaoyan22” and the low N efficiency “Xiaoyan6”) under different atmospheric CO₂ (375 μmol·mol^-1 and 750 μmol·mol^-1) and nitrogen amendments 0, 0.15 g(N)·kg^-1(soil) and 0.30 g(N)·kg^-1(soil) conditions were measured in open-top chamber (OTC) pot soil experiments. Results showed that while ear length and plant height of “Xiaoyan22” were significantly higher, leaf area and stem height were lower than those of “Xiaoyan6” for the di-atmospheric CO₂ (750 μmol·mol^-1) with nitrogen amended treatments. Compared with ambient atmospheric CO₂ level (375 μmol·mol^-1), di-CO₂ concentration (750 μmol·mol^-1) significantly improved yields of the two winter wheat varieties under N treatments. Yields of “Xiaoyan6” and “Xiaoyan22” were 90.5% and 52.9% greater under di-CO₂ concentration with 0.15 g(N)·kg^-1(soil) treatment and also 73.9% and 93.6% greater under di-CO₂ concentration with 0.30 g(N)·kg^-1(soil) treatment than those under the ambient CO₂ condition. Di-CO₂ concentration increased above-ground biomass, root biomass, total biomass, spikes per pot, grains per spike and yield of the two winter wheat varieties under the same nitrogen conditions. Although elevated N application exhibited no consistent effects on agricultural production, increasing N supply enhanced above-ground biomass, total biomass, grains per spike and yield. Above-ground biomass, total biomass, grains per spike and yield with di-CO₂ condition were higher under 0.30 g(N)·kg^-1(soil) treatment than under 0.15 g(N)·kg-1(soil) treatment. The results from this study indicated that increasing N supply benefited the positive effects of elevated CO₂ on crop production.