Modelling the timing of Betula pubescens budburst. I. Temperature and photoperiod: a conceptual model

Abstract

The main factors triggering and releasing bud dormancy are photoperiod and temperature. Their individual and combined effects are complex and change along a transition from a dormant to a non-dormant state. Despite the number of studies reporting the effects of temperature and photoperiod on dormancy release and budburst, information on the parameters defining these relationships is scarce. The aim of the present study was to investigate the effects and interaction of temperature and photoperiod on the rates of dormancy induction and release in Betula pubescens (Ehrh.) in order to develop a conceptual model of budburst for this species. We performed a series of controlled environment experiments in which temperature and photoperiod were varied during different phases of dormancy in B. pubescens clones. Endodormancy was induced by short days and low temperatures, and released by exposure to a minimal period of chilling temperatures. Photoperiod during exposure to chilling temperatures did not affect budburst. Longer exposure to chilling increased growth capability (growth rate at a given forcing temperature) and decreased the time to budburst. During the forcing phase, budburst was promoted by photoperiods above a critical threshold, which was not constant, but decreased upon longer chilling exposures. These relationships between photoperiod and temperature have, as yet, not been integrated into the commonly used processbased phenological models. We suggest models should account for these relationships to increase the accuracy of their predictions under future climate conditions. KEY WORDS: Betula pubescens · Controlled environment experiments · Phenology · Photoperiod · Temperature · Dormancy · Budburst Resale or republication not permitted without written consent of the publisherClim Res 46: [147][148][149][150][151][152][153][154][155][156][157] 2011 1995, Thomas & Vince Prue 1997). The action of these environmental drivers is complex and changes along the transition from a dormant to a non-dormant state. In addition, it has been shown that photoperiod and temperature interact at various stages during dormancy induction, release and quiescence (Håbjørg 1972, Junttila 1980, Heide 1993, 2003, Myking & Heide 1995, Partanen et al. 2001.Photoperiod affects the time at which buds enter a phase of winter rest. Short days (ShDs) signal the onset of winter, which, in turn, triggers decreasing 'growth competence' (growth capability). Once the plant has been exposed to a certain number of dormancyinductive days (dormancy induction requirement), the phase of endodormancy is reached, a period during which buds do not grow even under favourable environmental conditions (Downs & Borthwick 1956, Håb-jørg 1972, Howe et al. 1996, Thomas & Vince Prue 1997, Welling et al. 1997.Chilling temperatures are the main trigger for endodormancy release (Perry 1971, Sarvas 1974, Cannell & Smith 1983, Battey 2000. The concept of 'chilling temperature' is not clearly defined, and a consistent response to chilling has not been ...

Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

“…1). Indeed, it has been assumed since the beginning of the twentieth century that, for the majority of temperate and boreal tree species, a certain duration of chilling temperatures ranging between 0 and 5°C is responsible for the release from endodormancy (Coville 1920;Sarvas 1974;Hänninen 1990;Caffarra et al 2011b). However, the range of chilling temperatures required for an efficient release from endodormancy has not yet been clearly identified (Dantec et al 2014).…”

“…Recent advances suggest that this range of chilling temperature is likely to be species-specific (Laube et al 2014) and may cover a broader spectrum than commonly assumed (Harrington et al 2010). Once endodormancy is released, warm temperatures have a clear positive effect on bud development during ecodormancy, with a warmer spring leading to an earlier budburst (Sarvas 1972;Sarvas 1974;Campbell and Sugano 1975;Lang et al 1987;Caffarra et al 2011b). The influence of warm spring temperatures is particularly obvious in mountainous areas, where tree populations flush gradually later toward higher elevations (Vitasse et al 2009), with only a small fraction of the variability explained by the genetic differentiation among populations .…”

“…The influence of warm spring temperatures is particularly obvious in mountainous areas, where tree populations flush gradually later toward higher elevations (Vitasse et al 2009), with only a small fraction of the variability explained by the genetic differentiation among populations . Finally, several studies have suggested that the influence of a warm temperature in early spring depends on the state of bud endodormancy and, in certain species (such as Fagus sylvatica or Picea abies), on the current photoperiod (Heide 1993;Myking and Heide 1995;Caffarra et al 2011b;Vitasse and Basler 2013;Basler and Körner 2014;Laube et al 2014). However, the effect of the photoperiod on the resumption of bud cell division and growth during ecodormancy varies widely among species and has been reported to clearly affect the timing of budburst in only one third of the temperate and boreal tree species for which this factor has been explicitly tested in experiments (18 out of 55 tree species, mainly temperate trees; Way and Montgomery 2014).…”

Nonlinear flowering responses to climate: are species approaching their limits of phenological change?

“…Along these lines, photoperiod can cue flowering in alpine plants when snowmelt is early, thereby setting a limit to how early plants can flower [17,25]. At the same time, plants may be able to adjust their photoperiod thresholds to match local site conditions, and temperature can override photoperiod [17,26,27]. Therefore, photoperiod may not always act to limit to how early plants can flower.…”

“…At least two studies have shown that flowering phenology in a few species can exhibit a threshold or nonlinear response to the timing of spring snowmelt (sensu figure 1a; [15,23]), and plant phenology is often modelled using nonlinear temperature functions [27,34,35]. However, the prevalence of these types of long-term responses within plant communities is largely unknown.…”