Effects of elevated [CO2] on leaf elongation under different nitrogen conditions mediated by auxin in tall fescue.

Leaf elongation is a crucial factor controlling forage production and is sensitive to environmental factors including CO2 concentration ([CO2]) and nitrogen (N). The objectives of this study were to examine the effects of elevated [CO2] on leaf elongation and clarify the underlying regulatory mechanism related to auxin metabolism in tall fescue (Festuca arundinacea. cv. 'Barlexas') under different N levels. Plants treated with low N level (0.25 mM) and moderate N level (4 mM) were exposed to ambient [CO2] (400 μmol⋅mol-1) or elevated [CO2] (800 μmol⋅mol-1) in environment-controlled growth chambers. Elevated [CO2] increased leaf elongation by stimulating cell division and elongation, regardless of the N conditions. The promotion of leaf elongation by elevated [CO2] was more pronounced under moderate N supply. Further results indicated that exogenous naphthylacetic acid treatment and endogenous overexpression of auxin biosynthesis gene FaYUCCA11 counteracted elevated [CO2]-induced promotion of leaf elongation under different N levels. The results demonstrated that auxin mediated the differential effects of elevated [CO2] on leaf elongation in tall fescue under different N availability regimes. Our results provide novel strategies for breeding new varieties of Poaceae grasses that will produce high biomass with minimal fertilizer inputs.