Contrasting responses of autumn-leaf senescence to daytime and night-time warming

Plant phenology is a sensitive indicator of climate change(1-4) and plays an important role in regulating carbon uptake by plants(5-7). Previous studies have focused on spring leaf-out by daytime temperature and the onset of snow-melt time(8,9), but the drivers controlling leaf senescence date (LSD) in autumn remain largely unknown(10-12). Using long-term ground phenological records (14,536 time series since the 1900s) and satellite greenness observations dating back to the 1980s, we show that rising pre-season maximum daytime (T-day) and minimum night-time (T-night) temperatures had contrasting effects on the timing of autumn LSD in the Northern Hemisphere (>20 degrees N). If higher T-day leads to an earlier or later LSD, an increase in T-night systematically drives LSD to occur oppositely. Contrasting impacts of daytime and night-time warming on drought stress may be the underlying mechanism. Our LSD model considering these opposite effects improved autumn phenology modelling and predicted an overall earlier autumn LSD by the end of this century compared with traditional projections. These results challenge the notion of prolonged growth under higher autumn temperatures, suggesting instead that leaf senescence in the Northern Hemisphere will begin earlier than currently expected, causing a positive climate feedback.