Organ-specific rest and quiescence in response to chilling and forcing in subtropical Torreya grandis trees

Winter rest and chilling accumulation play a crucial role in regulating the leaf-out and flowering of extratropical woody plants. Still, there is a lack of understanding regarding the potential rest condition of overwintered immature cones of coniferous trees and how the dormancy of different organ types responds to environmental cues. To address this gap, we conducted a unique experimental design using 8–10-year-old potted adult Torreya grandis trees. We examined the rest condition in leaf buds, flower buds, and overwintered immature nuts (cones) simultaneously, and we summarized our findings with process-based models. Our results revealed that overwintered nuts, too, exhibit a rest condition and a chilling requirement similar to those of leaf and flower buds. The effects of photoperiod on rest break were minor in general, so that we did not include photoperiod in our process-based models. The upper limit of an effective chilling temperature was lower for the nuts (<13 °C) than for the flower and leaf buds (<17 °C). During the quiescence period after rest completion, a low forcing temperature of 10 °C enabled ontogenetic development in the nuts and the flower buds but not in the leaf buds. Despite these differences, our models predicted an almost identical change rate for the spring phenology under climate warming in the three organ types. Organ-specific phenological responses provide valuable insights into the impact of environmental factors on plant growth and development.