Three times greater weight of daytime than of night-time temperature on leaf unfolding phenology in temperate trees.

Yongshuo H Fu,Shilong Piao,Marc Peaucelle,Josep Peñuelas,Ivan A Janssens,Annette Menzel,Hans J De Boeck,Yongjie Liu,Ivan Nijs

doi:10.1111/nph.14073

Abstract

The phenology of spring leaf unfolding plays a key role in the structure and functioning of ecosystems. The classical concept of heat requirement (growing degree days) for leaf unfolding was developed hundreds of years ago, but this model does not include the recently reported greater importance of daytime than night-time temperature. A manipulative experiment on daytime vs night-time warming with saplings of three species of temperate deciduous trees was conducted and a Bayesian method was applied to explore the different effects of daytime and night-time temperatures on spring phenology. We found that both daytime and night-time warming significantly advanced leaf unfolding, but the sensitivities to increased daytime and night-time temperatures differed significantly. Trees were most sensitive to daytime warming (7.4±0.9, 4.8±0.3 and 4.8±0.2d advancement per degree Celsius warming (d °C-1 ) for birch, oak and beech, respectively) and least sensitive to night-time warming (5.5±0.9, 3.3±0.3 and 2.1±0.9d°C-1 ). Interestingly, a Bayesian analysis found that the impact of daytime temperature on leaf unfolding was approximately three times higher than that of night-time temperatures. Night-time global temperature is increasing faster than daytime temperature, so model projections of future spring phenology should incorporate the effects of these different temperatures.

Highlights

Plant phenology is highly sensitive to climate change (Menzel et al, 2006; Schwartz et al, 2006; Jeong et al, 2011; Fu et al, 2014b)
The growing degree hours (GDH) calculated from 1 January 2014 to the day of leaf unfolding were significantly larger for trees in the three warming treatments than for those in the control treatments for all three species (Fig. 2C), even though the dates of leaf unfolding were significantly advanced for the trees in the warming treatments (Fig. 2A)
Among the three warming treatments, we found that earlier leaf unfolding was associated with less GDH accumulation, the GDH accumulation did not differ significantly among the three warming treatments

Summary

Introduction

Plant phenology is highly sensitive to climate change (Menzel et al, 2006; Schwartz et al, 2006; Jeong et al, 2011; Fu et al, 2014b). Other environmental factors have recently been associated with leaf unfolding, such as winter chilling (Murray et al, 1989; Fu et al, 2013; Laube et al, 2014a), photoperiod (Körner & Basler, 2010; Way & Montgomery, 2014), humidity (Laube et al, 2014b), precipitation (Penuelas et al, 2004; Fu et al, 2014c) and conditions in the previous year (Fu et al, 2014a) Taking advantage of these findings, models that include GDD and chilling and photoperiod (Hänninen & Kramer, 2007; Chuine et al, 2013)

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Conclusion