Heat, wheat and CO 2 : The relevance of timing and the mode of temperature stress on biomass and yield

Atmospheric CO 2 enrichment affects C3 crops both directly via increased carbon gain and improved water use efficiency and indirectly via higher temperatures and more frequent climatic extremes. Here we investigated the response of spring wheat ( Triticum aestivum L. cv. Triso) to CO 2 enrichment (550 vs. 380 µmol/mol) and heat, applied as a constant +4°C increase or a typical heat wave either before or after anthesis, or as two typical heat waves before and after anthesis. We applied a climate chamber approach closely mimicking ambient conditions. CO 2 enrichment increased above‐ground biomass and yield by c. 7 and 10%, but was not able to compensate for adverse heat stress effects, neither before nor after anthesis, with few exceptions only. Yield depression due to heat stress was most severe when two heat waves were applied (−19%). This adverse effect was, however, compensated by CO 2 enrichment. Applying heat stress before or after anthesis did not exert different effects on yield for both +4°C warming and heat wave application. However, +4°C depressed yield more than a heat wave at ambient CO 2 , but not so at elevated CO 2 . Thus, the interactive effects were complex and prediction of future wheat yield under CO 2 enrichment and climate extremes deserves more attention.