Larger responses of trees' leaf senescence to cooling than warming: Results from a climate manipulation experiment

Global warming generally delays autumn leaf senescence, which affects carbon and water cycles of terrestrial ecosystem and exerts feedbacks on the climate system. Nevertheless, several regions in the Northern Hemisphere have experienced autumn cooling since the start of the 21st century. Whether cooling affects leaf senescence to the same extent as warming is currently unclear. In this study, we conducted a manipulative experiment with warming or cooling treatments imposed during summer and autumn on saplings of ginkgo and oak to investigate the effects of seasonal warming and cooling on leaf senescence. In addition, two light intensity and photoperiod treatments were applied to study their interactive effects with temperature on leaf senescence. We found that the temperature sensitivity of leaf senescence (ST) was significantly larger in autumn (5.4-6.4 days & DEG;C-1) than in summer (0.6-2.4 days & DEG;C-1). Interestingly, cooling had a larger effect on leaf senescence than warming, with a significantly higher ST under cooling (1.7-3.5 days & DEG;C-1 in summer and 8.5-11.6 days & DEG;C-1 in autumn) than under warming (0.8-1.0 days & DEG;C-1 and 0.3-1.8 days & DEG;C-1). Furthermore, higher light intensity significantly decreased the temperature sensitivity of leaf senescence especially in autumn, i.e. ST was 3.8 and 6.1 days & DEG;C-1 under high light intensity condition, but the ST was 8.2 and 8.0 days & DEG;C-1 under low light intensity, for ginkgo and oak, respectively. Our results suggest unequal effects of cooling and warming on leaf senescence, and radiation affects the leaf senescence processes by altering its temperature sensitivity. These findings enrich our understanding of leaf senescence and could be integrated into the ecosystem models to improve their performance.

Automated summary

Global warming usually delays autumn leaf senescence, impacting carbon and water cycles and climate. However, some regions in the Northern Hemisphere have experienced autumn cooling since the early 21st century. It is unclear whether cooling affects leaf senescence to the same extent as warming. This study conducted an experiment with warming or cooling treatments on ginkgo and oak saplings to investigate the effects of seasonal temperature changes on leaf senescence.