Responses of wheat and rice to factorial combinations of ambient and elevated CO₂ and temperature in FACE experiments

<p>Elevated CO₂ and temperature strongly affect crop production, but understanding of the crop response to combined CO₂ and temperature increases under field conditions is still limited while data are scarce. We grew wheat (Triticum aestivum L.) and rice (Oryza sativa L.) under two levels of CO₂ (ambient and enriched up to 500 μmol mol^-1) and two levels of canopy temperature (ambient and increased by 1.5-2.0 °C) in free-air CO₂ enrichment (FACE) systems and carried out a detailed growth and yield component analysis during two growing seasons for both crops. An increase in CO₂ resulted in higher grain yield, whereas an increase in temperature reduced grain yield, in both crops. An increase in CO₂ was unable to compensate for the negative impact of an increase in temperature on biomass and yield of wheat and rice. Yields of wheat and rice were decreased by 10-12% and 17-35%, respectively, under the combination of elevated CO₂ and temperature. The number of filled grains per unit area was the most important yield component accounting for the effects of elevated CO₂ and temperature in wheat and rice. Our data showed complex treatment effects on the interplay between preheading duration, nitrogen uptake, tillering, leaf area index, and radiation-use efficiency, and thus on yield components and yield. Nitrogen uptake before heading was crucial in minimizing yield loss due to climate change in both crops. For rice, however, a breeding strategy to increase grain number per m² and % filled grains (or to reduce spikelet sterility) at high temperature is also required to prevent yield reduction under conditions of global change.