Unravelling the causes for reduced grain protein under elevated CO2

S Tausz-Posch1, H Bahrami1, GJ Fitzgerald2, R Armstrong2, P Buchner3 and M Tausz1

  1. The University of Melbourne, Creswick VIC 3363, Australia
  2. Department of Economic Development, Jobs, Transport and Resources, Horsham, Australia
  3. Rothamsted Research, Harpenden, UK

Atmospheric CO2 [CO2] is predicted to reach a concentration of ~550 ppm by 2050. This ~35% rise from a current [CO2] of ~400 ppm is affecting plant performance. In wheat, e.g., above- and below ground biomass as well as grain yield is stimulated while grain N and thus protein concentrations are reduced, negatively affecting the nutritional and market value of grains. In order to unravel and overcome N reductions under elevated CO2 (e[CO2]), the following questions were investigated: (1) Are differences in root growth associated with differences in N status under e[CO2]? (2) Does nitrate accumulate in leaves of e[CO2]-grown wheat indicating impaired nitrate reduction? (3) Is N remobilisation from leaves into grains and expression of related genes affected by e[CO2], thereby contributing to grain N reductions? Questions were tested on field-grown wheat under ambient (a[CO2]) or e[CO2] (~550 ppm) within the Australian Grains Free Air CO2 Enrichment (AGFACE) program. Root growth was stimulated by e[CO2], but was not related with grain N status. In contrast, the ratio of nitrate to total N in leaves was greater under e[CO2] and was significantly related to decreased grain N. Also, a range of genes relating to N and C metabolism was up-regulated in senescing leaves under a[CO2] but no such up-regulation was observed under e[CO2]. We suggest that (1) CO2 enrichment impaired nitrate reduction so that, despite sufficient N uptake, unassimilated nitrate accumulated in leaves and (2) CO2 enrichment caused a greater demand for N translocation into the developing grain which was not met.