Elevated carbon dioxide ameliorates the effect of Zn deficiency and terminal drought on wheat grain yield but compromises nutritional quality

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Official URL: http://dx.doi.org/10.1007/s11104-016-2996-9

Elevated atmospheric carbon dioxide (CO2) has a positive impact on grain yield as a consequence of increased photosynthetic rate and efficient utilization of water, but may negatively affect nutritional quality of the grains. This study aimed at revealing the impact of elevated CO2 and terminal drought on yield performance and nutritional status of bread wheat as affected by Zn availability in soil. Bread wheat (T. aestivum cv. Tahirova) was grown in soil culture (DTPA-Zn: 0.59 mg kg(-1)) with adequate (2 mg Zn kg(-1) soil) and low Zn supply (no Zn added) in climate chambers, under ambient (400 mu mol mol(-1)) and elevated atmospheric CO2 (700 mu mol mol(-1)). Terminal drought stress was initiated at the onset of flowering stage by reducing the soil moisture to first 45 % and then gradually to 25 % of field capacity. Fully mature plants were harvested to determine yield, yield components, and grain Zn and protein concentration. Low Zn supply and terminal drought stress resulted in decreased grain and straw yield, whereas elevated CO2 enhanced grain and straw yield under Zn-limited and/or drought-stressed conditions. Increase in grain yield was a function of increased spike number. Elevated CO2 also induced Zn-efficiency (i.e. ability to yield highly at low Zn supply), but resulted in reduced grain Zn concentration and content. Grain protein concentrations were lower in elevated CO2, but higher in low Zn and drought conditions, due to "dilution" and "concentration" effects respectively. Biomass enhancement ratio (i.e. yield enhancement by elevated CO2) was not affected by Zn supply, but increased in drought-stressed plants. Elevated CO2 can increase biomass production and grain yield even under low productivity conditions such as low water and/or Zn availability, but can reduce the nutritional value of the grain in terms of Zn and protein concentration. Adequate Zn supply is required to fill the dilution gap that is likely to arise with increasing atmospheric CO2 and changes in the distribution of precipitation.