The proportion of nitrate in leaf nitrogen, but not changes in root growth, are associated with decreased grain protein in wheat under elevated [CO2]
De Kok, Luit J.
Fitzgerald, Glenn J.
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The atmospheric CO2 concentration ([CO2]) is increasing and predicted to reach âˆ¼550 ppm by 2050. Increasing [CO2] typically stimulates crop growth and yield, but decreases concentrations of nutrients, such as nitrogen ([N]), and therefore protein, in plant tissues and grains. Such changes in grain composition are expected to have negative implications for the nutritional and economic value of grains. This study addresses two mechanisms potentially accountable for the phenomenon of elevated [CO2]-induced decreases in [N]: N uptake per unit length of roots as well as inhibition of the assimilation of nitrate (NO3âˆ’) into protein are investigated and related to grain protein. We analysed two wheat cultivars from a similar genetic background but contrasting in agronomic features (Triticum aestivum L. cv. Scout and Yitpi). Plants were field-grown within the Australian Grains Free Air CO2 Enrichment (AGFACE) facility under two atmospheric [CO2] (ambient, âˆ¼400 ppm, and elevated, âˆ¼550 ppm) and two water treatments (rain-fed and well-watered). Aboveground dry weight (ADW) and root length (RL, captured by a mini-rhizotron root growth monitoring system), as well as [N] and NO3âˆ’ concentrations ([NO3âˆ’]) were monitored throughout the growing season and related to grain protein at harvest. RL generally increased under e[CO2] and varied between water supply and cultivars. The ratio of total aboveground N (TN) taken up per RL was affected by CO2 treatment only later in the season and there was no significant correlation between TN/RL and grain protein concentration across cultivars and [CO2] treatments. In contrast, a greater percentage of N remained as unassimilated [NO3âˆ’] in the tissue of e[CO2] grown crops (expressed as the ratio of NO3âˆ’ to total N) and this was significantly correlated with decreased grain protein. These findings suggest that e[CO2] directly affects the nitrate assimilation capacity of wheat with direct negative implications for grain quality.
Bahrami, Helale, Luit J. De Kok, Roger Armstron, Glenn J. Fitzgerald, Maryse Bourgault, Samuel Henty, Michael Tausz, and Sabine Tausz-Posch. "The proportion of nitrate in leaf nitrogen, but not changes in root growth, are associated with decreased grain protein in wheat under elevated [CO2]." Journal of Plant Physiology (May 2017). DOI: 10.1016/j.jplph.2017.05.011.