Nitrogen nutrition and aspects of root growth and function of two wheat cultivars under elevated [CO2]

When grown in the Australian Grains Free Air CO2 Enrichment facility over multiple seasons both cultivars produced similar yields, but 'Silverstar' had consistently lower grain [N], smaller grains and greater harvest index. In situ N uptake measurements with 15N label showed that wheat roots can take up nitrate, ammonium and glutamine, and also confirmed differences in uptake strategies between cultivars: 'Silverstar' roots had significantly greater uptake capacity than 'Yitpi' roots for ammonium. Whilst these results suggest that different strategies in response to variations in soil N supply could be related to grain N outcomes at this field site, there was no interaction with atmospheric [CO2] for any of the measured parameters. Regardless of cultivar, elevated [CO2] (550 μmol mol−1) increased yields and decreased grain [N], but did not affect root uptake capacities for either N form. Contrasting root uptake strategies seem unrelated to grain [N] decrease under elevated [CO2], at least for this site.