Ecosystem warming extends vegetation activity but heightens vulnerability to cold temperatures
Ecosystem warming extends vegetation activity but heightens vulnerability to cold temperatures
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DOI：
10.1038/s41586-018-0399-1
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发表时间：
2018-08-16
期刊：
影响因子：
64.8
通讯作者：
Hanson, Paul J.
中科院分区：
文献类型：
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作者：
Richardson, Andrew D.;Hufkens, Koen;Hanson, Paul J.
植被物候变化是气候变化生物效应的一个重要例子（1-3）。然而，这些由温度驱动的趋势是否会继续下去，或者其他因素（如光周期）是否会随着变暖超过历史变率的界限而变得更加重要，这些都存在很大的不确定性（4,5）。在这里，我们使用来自数字重复摄影(5)的物候过渡日期(6)来表明，在北方云杉-泥炭沼泽中，高达+9摄氏度的实验全生态系统升温处理(7)与优势木本物种的秋季延迟绿化和春季提前绿化呈线性相关。通过对这些植物和其他沼泽植物的营养和生殖物候的直接观察，以及多年的观察，证实了这一结果。几乎没有证据表明观测到的响应受光周期的限制。我们的研究结果表明，到21世纪末，在“二氧化碳稳定”气候情景（+2.6 +/- 0.7℃）下，植被活动期可能延长1-2周，在“二氧化碳高排放”情景（+5.9 +/- 1.1℃）下，植被活动期可能延长3-6周。我们还观察到在一个严重的春季霜冻事件后，在最温暖的围栏中严重的组织死亡。未能响应光周期导致早熟绿化和抗冻性过早丧失(8)，这表明在一个更温暖的世界中，对春季霜冻损害的脆弱性将增加（9,10）。在历史气候条件下，为平衡与物候温度跟踪相关的权衡而进化的植被策略可能是最优的，但这些策略可能不适合未来的气候条件。这些实地实验结果特别重要，因为北方森林既具有环极分布，又在全球碳循环中发挥关键作用（11）。
Shifts in vegetation phenology are a key example of the biological effects of climate change(1-3). However, there is substantial uncertainty about whether these temperature-driven trends will continue, or whether other factors-for example, photoperiod-will become more important as warming exceeds the bounds of historical variability(4,5). Here we use phenological transition dates derived from digital repeat(5) photography(6) to show that experimental whole-ecosystem warming treatments(7) of up to +9 degrees C linearly correlate with a delayed autumn green-down and advanced spring green-up of the dominant woody species in a boreal Picea-Sphagnum bog. Results were confirmed by direct observation of both vegetative and reproductive phenology of these and other bog plant species, and by multiple years of observations. There was little evidence that the observed responses were constrained by photoperiod. Our results indicate a likely extension of the period of vegetation activity by 1-2 weeks under a 'CO2 stabilization' climate scenario (+2.6 +/- 0.7 degrees C), and 3-6 weeks under a 'high-CO2 emission' scenario (+5.9 +/- 1.1 degrees C), by the end of the twenty-first century. We also observed severe tissue mortality in the warmest enclosures after a severe spring frost event. Failure to cue to photoperiod resulted in precocious green-up and a premature loss of frost hardiness(8), which suggests that vulnerability to spring frost damage will increase in a warmer world(9,10). Vegetation strategies that have evolved to balance tradeoffs associated with phenological temperature tracking may be optimal under historical climates, but these strategies may not be optimized for future climate regimes. These in situ experimental results are of particular importance because boreal forests have both a circumpolar distribution and a key role in the global carbon cycle(11).