Can intra-specific differences in root traits of wheat increase nitrogen use efficiency (NUE) under elevated CO2?

The atmospheric CO2 concentration is predicted to reach ~550 ppm by the middle of this century. The observed negative effect of increased CO2 concentration on grain quality is of major concern. One strategy to compensate for this effect is to apply more N fertiliser. However, increased fertiliser costs as well as associated environmental concerns have stimulated growers to reevaluate their fertiliser application strategies with the aim of optimizing Nitrogen Use Efficiency (NUE) while maintaining crop yields and minimising N losses. Improving NUE through selection of specific root characteristic will be crucial to the adaptation of future climates. Because roots are the first plant organ that receive nutrients such as N from the soil, traits like root biomass, length and rooting depth can significantly affect N uptake rates and therefore NUE in crops. This study investigated the NUE and root biomass of two contrasting wheat (Triticum aestivum L.) cultivars (Scout and Yitpi) grown under two atmospheric CO2 concentrations (ambient, ~400 ppm, and elevated, ~550 ppm) and two N treatments (low, 21 mg N/core, and high, 250 mg N/core) at the Australian Grains Free Air CO2 Enrichment (AGFACE) facility in south-eastern Australia. Results showed that at anthesis, Scout had more N (g) in aboveground and whole plant while Yitpi recorded more N (g) in root biomass. At maturity, Yitpi still had more N in roots, but Scout recorded greater N in grains. While both cultivars uptake almost the same amount of N from the soil, Scout was more able to transfer this N from roots to aboveground biomass at anthesis and then to grains at maturity, which is a very important characteristic that can allow wheat to maintain grain quality under elevated CO2.