Warming-induced changes in bud dormancy and their effects on leaf phenology in common European tree species

春季落叶和秋季植物衰老的时间在很大程度上决定了植物生长季节的长度，并在生态系统的净生产力中起着重要作用。温暖的春季和秋季温度分别与春季提前落叶和延迟植物衰老密切相关。然而，最近观察到在过去几十年中，每度变暖的春季绿化的推进速度下降，反映了植物物候对气候变暖的非线性响应。未来的预测表明，对某些物种来说，春季脱叶的进展可能会停止甚至推迟。秋天的衰老更不可预测，新的证据表明，它可以在春天提前发芽后提前，并被温暖的秋季温度推迟。因此，了解气候变化引起的特定物种物候变化的机理，对于更好地预测未来生态系统功能、植物群落组成和动植物相互作用的变化至关重要。迄今为止，气候变化下植物物候的变化主要是以观察的方式解决的，将历史物候日期与温度记录相关联。最近，更好地了解芽休眠提供了一个更好的解释背后的生物控制萌芽日期。例如，在芽休眠诱导期间加温可以增加芽休眠深度，并导致春季萌芽延迟。因此，芽休眠的变化已开始纳入物候模型，并导致提高萌芽日期的预测。然而，芽休眠诱导的物种特异性光周期和/或温度控制尚不清楚，需要量化。植物物候并不仅仅是由秋季和春季的温度驱动的。芽休眠深度、光周期敏感性、季节性和年度延续效应已被证明是植物物候的重要驱动因素。因此，本项目的实验将主要集中在a）光周期和温度对芽休眠深度的相对影响，B）变暖引起的芽休眠深度的变化和c）春季物候时间对随后的叶片衰老和春季萌芽日期的影响。种间和种内变异将通过对欧洲常见树种和欧洲最重要的本土树种--林青冈（Fagus sylvatica）进行实验来量化。两者合计，温度和光周期的操纵将被用来量化种间和种内变暖引起的芽休眠变化和随后的叶物候变化。实验结果中，物候变化不仅仅是离开温度驱动的“黑匣子”的影响，但与芽休眠的具体变化将加深我们对植物物候的机械理解，并将是未来的物候模型的一个有价值的基础。

The timing of leaf-out in the spring and plant senescence in the fall largely determines the length of a plant’s growing season and plays a major role in the net productivity of an ecosystem. Warmer spring and fall temperatures have been closely linked with advanced spring leaf-out and delayed plant senescence, respectively. However, a recently observed reduction in the rate of advancement of spring green-up per degree of warming over the last decades reflects a nonlinear response of plant phenology to climate warming. Future projections indicate that for certain species, advancement in spring leaf-out can stop or even be delayed. Fall senescence is much more unpredictable, with new evidence showing that it can be advanced following an earlier budburst in the spring and be delayed by warmer fall temperatures. Understanding the mechanistic causes of species-specific shifts in phenology in response to climate change is thus essential to better project future changes in ecosystem functions, plant community compositions and plant-animal interactions. To date changes in plant phenology under climate change have mostly been addressed in an observational manner, correlating historical phenological dates with temperature records. Recently, a better understanding of bud dormancy has provided an improved explanation for the biological controls behind bud burst dates. For example, warming during bud dormancy induction can increase bud dormancy depth and lead to a delayed spring budburst. As a result, bud dormancy changes have started to be incorporated into phenological models and have led to improved budburst date predictions. The species-specific photoperiodic and/or temperature control of bud dormancy induction is not known however and needs to be quantified. Plant phenology is not simply driven by fall and spring temperatures. Bud dormancy depth, photoperiod sensitivity and seasonal as well as yearly carry-over effects have been shown to be important drivers of plant phenology. The experiments in this project will thus primarily focus on a) the relative influence of photoperiod and temperature on bud dormancy depth, b) warming-induced changes in bud dormancy depth and c) legacy effects of spring phenology timing on subsequent leaf senescence and spring budburst dates. Among- as well as within-species variation will be quantified by conducting the experiments on common European tree species and ecotypes of Fagus sylvatica, arguably the most important native tree species in Europe. Taken together, manipulation of temperature and photoperiod will be used to quantify among- and within-species variation in warming-induced bud dormancy changes and subsequent leaf phenology. Experimental results where phenological changes are not merely left to temperature-driven "black box" effects but are linked to specific changes in bud dormancy will deepen our mechanistic understanding of plant phenology and will be a valuable basis for future phenology models.