Night temperature determines nearly half of wheat yield variation globally

Daily minimum temperature (Tmin) is increasing faster than maximum temperature. However, its impact on the physiology of crop yield and adaptation is barely studied. Using 42 years of annual yield trials at 255 sites representing most spring wheat production regions, the effects of environmental covariates were examined. Average Tmin during grain filling explained 40% of the variation in yield, and 52% when also considering radiation. Generally, an increase of 1ºC reduces yield by ~0.5 t/ha. The relation between yield was linear over a 14ºC range. An average increase of 1.2ºC at the test sites reduced yield by more than 10%. A shortened grain filling period is part of the explanation; nocturnal rates of dark respiration are also likely factors. Improvement in adaptation to warmer nights could generate a step-change in wheat yield, the most widely-grown crop globally, covering more than 220 million ha and providing 20% of human calories and protein.