Chill and heat accumulation modulates phenology in temperate fruit trees


Temperature is the main environmental driver of temperate fruit tree phenology. Rising temperatures due to global warming are clearly affecting this trait. However, predicting the effects of temperature variation on tree phenology is challenging since the relationship between specific temperatures during the cold season and bloom dates remains unclear. Buds of temperate fruit trees, which host the meristems, establish a dormant state during winter. To overcome dormancy, buds require exposure to low temperatures and subsequent warm conditions that trigger the resumption of growth. Most phenological studies require extensive bloom date records, which need many years of observations. An alternative approach, which produces comparable data sets much more quickly, is the use of multiple environments, where young potted trees can be exposed to different temperature regimes during dormancy. We used this approach to generate multi-season phenology data for apple, pear and sweet cherry trees. We found that earliest bloom dates were associated with a large amount of heat after low chill accumulation. These findings may support the development of new modeling frameworks that can help anticipate the impacts of climate change on tree dormancy.