Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Global warming is diurnally asymmetric, leading to a less-cold, rather than warmer, climate. We investigated the effects of asymmetric experimental warmings on plant phenology by testing the hypothesis that daytime warming is more effective in advancing bud break than nighttime warming. Bud break was monitored daily in Picea mariana seedlings belonging to 20 provenances from Eastern Canada and subjected to daytime and nighttime warmings in growth chambers at temperatures varying between 8 and 16 °C. The higher advancements of bud break and shorter times required to complete the phenological phases occurred with daytime warming. Seedlings responded to nighttime warming, but still with less advancement of bud break than under daytime warming. No advancement was observed when nighttime warming was associated to a daytime cooling. The effect of the treatments was uniform across provenances. Our observations realized under controlled conditions allowed to experimentally demonstrate that bud break can advance under nighttime warming, but to a lesser extent than under daytime warming. Prediction models using daily time scales could neglect the diverging influence of asymmetric warming and should be recalibrated for higher temporal resolutions.