Abstract
The effects of winter chilling, spring forcing temperature, and photoperiod on spring phenology are well known for many European and North American species, but the environmental cues that regulate the spring phenology of East Asian species have not yet been thoroughly investigated. Here, we conducted a growth chamber experiment to test the effects of chilling (controlled by different lengths of exposure to natural chilling conditions), forcing temperature (12, 15, or 18°C) and photoperiod (14 or 10 h) on first flowering date (FFD) of six woody species (three shrubs and three trees) native to East Asia. The three-way analysis of variance (ANOVA) separately for each species showed that the effects of chilling and forcing temperature were significant for almost all species (P < 0.05). Averaged over all chilling and photoperiod treatments, the number of days until FFD decreased by 2.3–36.1 days when the forcing temperature increased by 3°C. More chilling days reduced the time to FFD by 0.7–26 days, when averaged over forcing and photoperiod treatments. A longer photoperiod could advance the FFD by 1.0–5.6 days, on average, but its effect was only significant for two species (including one tree and one shrub). The effects of forcing temperature and photoperiod interacted with chilling for half of the studied species, being stronger in the low chilling than high chilling treatment. These results could be explained by the theory and model of growing degree-days (GDD). Increased exposure to chilling coupled to a longer photoperiod reduced the GDD requirement for FFD, especially when plants grew under low chilling conditions. However, shrubs (except Viburnum dilatatum) had lower chilling and heat requirements than trees, suggesting that, by leafing out sooner, they engage in a more opportunistic life strategy to maximize their growing season, especially before canopy closure from trees' foliage. Our results confirmed the varying effects of these three cues on the flowering phenology of woody species native to East Asia. In future climate change scenarios, spring warming is likely to advance the spring phenology of those woody species, although the reduced chilling and shorter photoperiod may partly offset this spring warming effect.
Highlights
The changed timing of recurring biological events becomes a global concern against the background of climate warming
In Asia, one study did assess the effect of forcing temperature on budburst date (Wang et al, 2019a), no multispecies study has yet evaluated all three major cues through the controlled experiment approach. To begin filling this knowledge gap, this study focused on six woody plants originating from East Asia, to investigate how different chilling, forcing temperature, and photoperiod treatments vary in their effects on spring phenology
Our results indicate that increasing the forcing temperature significantly promotes the first flowering date (FFD) of woody plants, which is consistent with findings on spring phenology of other species, such as leaf budburst in Betula pubescens (Caffarra et al, 2011), Fagus sylvatica, Tilia cordata, Salix x smithiana (Caffarra and Donnelly, 2011) and 28 woody species from two North American forests (Flynn and Wolkovich, 2018)
Summary
The changed timing of recurring biological events becomes a global concern against the background of climate warming. The earlier spring phenophases (e.g., budburst date, leaf-out date) and later autumn phenophases (e.g., leaf coloring date) of woody plants were observed over the past several decades in middle and high latitudes of the Northern Hemisphere (Chmielewski and Rötzer, 2001; Menzel et al, 2006; Gonsamo et al, 2013; Ge et al, 2015; Templ et al, 2017). Such climate-associated phenological change could influence carbon assimilation by modifying the length of the growing season (Keenan et al, 2014; Xia et al, 2015). In order to adequately predict the future dynamics in vegetation–climate systems and their modeling, it is essential to understand the driving factors of plant phenology
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