Late to bed, late to rise—Warmer autumn temperatures delay spring phenology by delaying dormancy

Abstract

Spring phenology of temperate forest trees has advanced substantially over the last decades due to climate warming, but this advancement is slowing down despite continuous temperature rise. The decline in spring advancement is often attributed to winter warming, which could reduce chilling and thus delay dormancy release. However, mechanistic evidence of a phenological response to warmer winter temperatures is missing. We aimed to understand the contrasting effects of warming on plants leaf phenology and to disentangle temperature effects during different seasons. With a series of monthly experimental warming by ca. 2.4°C from late summer until spring, we quantified phenological responses of forest tree to warming for each month separately, using seedlings of four common European tree species. To reveal the underlying mechanism, we tracked the development of dormancy depth under ambient conditions as well as directly after each experimental warming. In addition, we quantified the temperature response of leaf senescence. As expected, warmer spring temperatures led to earlier leaf‐out. The advancing effect of warming started already in January and increased towards the time of flushing, reaching 2.5 days/°C. Most interestingly, however, warming in October had the opposite effect and delayed spring phenology by 2.4 days/°C on average; despite six months between the warming and the flushing. The switch between the delaying and advancing effect occurred already in December. We conclude that not warmer winters but rather the shortening of winter, i.e., warming in autumn, is a major reason for the decline in spring phenology.

Warming may extend tree growing seasons and compensate for reduced carbon uptake during dry periods

“…Our results support previous studies showing that global warming induces earlier tree activity (e.g. Beil et al, 2021; Piao et al, 2019; Vitasse et al, 2018). In addition, our results demonstrate that temperature impacts on spring phenology are independent of soil moisture in temperate trees as an advanced leaf unfolding occurred even when warming was combined to a substantial irrigation reduction (i.e.…”

“…If warming occurs early in the growing season, it should stimulate photosynthesis when growth demand is high and prolong senescence. However, warming could accelerate autumn phenology if it occurs towards the end of the growing season when growth demand is low (Beil et al, 2021). As our treatments were applied all along the growing season, the two effects may have been triggered and compensated for each other.…”

ABA and Not Chilling Reduces Heat Requirement to Force Cherry Blossom after Endodormancy Release

“…Since ABA inhibits bud development, it can be assumed that heat accumulated shortly after t 1 does not have the same effect on bud development as during ontogenetic development, when the bud’s ABA content is already reduced by about ~50%. This would generally explain the reduction in the forcing requirement or the declining dormancy depth during ecodormancy [ 38 ], which is, according to our findings (correlation analysis between ΔABA, ΔS c (t), Section 2.4 . ), not the result of additional chilling.…”

Applying Plant Hydraulic Physiology Methods to Investigate Desiccation During Prolonged Cold Storage of Horticultural Trees

“…Maintaining urban forests, wildland restoration, and reforestation are challenged by the environmental conditions associated with climate change, like extreme heatwaves, that make it more difficult for trees to survive after planting. Warm autumn temperatures delay dormancy and planting windows are more unpredictable ( Beil et al, 2021 ; Fargione et al, 2021 ). Extreme weather puts even more pressure on nursery professionals to understand how plant physiology, including water relations and carbon dynamics, responds to each stage of the nursery production process ( Sheridan and Nackley, 2021 ).…”