Effects of chill unit accumulation and temperature on woody plant deacclimation kinetics

Abstract

Woody perennials in temperate climates develop cold hardiness in the fall (acclimation) and lose cold hardiness in the spring (deacclimation) to survive freezing winter temperatures. Two main factors known to regulate deacclimation responses are dormancy status and temperature. However, the progression of deacclimation responses throughout the dormant period and across a range of temperatures is not well described. More detailed descriptions of dormancy status and temperature, as factors regulating deacclimation, are necessary to understand the timing and magnitude of freeze injury risks for woody perennials in temperate climates. In this study, we modeled deacclimation responses in cold‐climate interspecific hybrid grapevine cultivars throughout the dormant period by integrating chill accumulation and temperature through the concept of deacclimation potential. We evaluated deacclimation and budbreak under multiple temperature treatments and chill unit accumulation levels using differential thermal analysis (DTA) and bud forcing assays. Deacclimation responses increased continuously following logistic trends for both increasing chill unit accumulation and increasing temperature. There are optimal temperatures where deacclimation rates increased but changes in deacclimation rates diminished below and above these temperatures. The cumulative chill unit range where deacclimation potential increased overlapped with the transition from endo‐ to ecodormancy. Therefore, deacclimation potential could provide a quantitative method for describing dormancy transitions that do not rely on the visual evaluation of budbreak. This information provides a more detailed understanding of when and how deacclimation contributes to increased risks by freezing injury. In addition, our descriptions could inform improvements to models predicting cold hardiness, dormancy transitions, and spring phenology.

Development of a new cold hardiness prediction model for grapevine using phased integration of acclimation and deacclimation responses

“…vinifera cultivars (Kovaleski et al, 2018) and a few hybrids (North et al, 2022), though not 'Concord'.…”

“…In addition to the rate 268 obtained through the partial derivative, a 0.001 (or 0.1%) rate was added to acclimation at all times. This 269 was incorporated to acknowledge anecdotal observations that buds seem to continue acclimating when 270 previous empirical experiments on grapevines and other species (Kovaleski et al, 2018;Kovaleski, 2022;North et al, 2022). One is for the rate of deacclimation (k deacc ) that any given temperature elicits.…”

“…One is for the rate of deacclimation (k deacc ) that any given temperature elicits. Other functions have been used to describe k deacc , such as a logistic (Chuine, 2000;North et al, 2022), combination of exponential and logarithmic (Kovaleski et al 2018) or a third-degree polynomial (Kovaleski, 2022). Here, the temperature response curve used was that based on a temperaturephotosynthesis curve (O'Neil et al, 1972):…”

Time to budbreak is not enough: cold hardiness evaluation is necessary in dormancy and spring phenology studies

“…However, these experiments have not included evaluations of cold hardiness in response to chilling. The combined effects of chilling and cold hardiness on time to budbreak have only been studied in field conditions, although this has now been done in many species, both of fruit crops, such as grapevines (Kovaleski et al, 2018; Kovaleski 2022; North et al, 2022) and apricot (Kovaleski, 2022), and other ornamental and forest species (Lenz et al, 2013; Vitra et al, 2017; Kovaleski, 2022). However, artificial chilling experiments are key to better understand effects of particular temperatures in providing chilling, as field conditions are too variable for this.…”

“…This means that for every two additional degrees Celsius of cold hardiness, buds will take an additional day to break bud. The inverse of this slope is also useful: if we consider budbreak occurs at the end of the cold hardiness loss period, we can estimate a deacclimation rate of approximately 2 ºC day -1 based on these data (approximately the maximum deacclimation rate reported by North et al (2022) for the same cultivars). Here this is measured at high levels of chill accumulation, after 3.5 months under chilling treatments, where deacclimation responses are likely maximized.…”