Department of Environmental Systems Science, Institute of Agricultural Sciences, ETH Zurich, Zurich, Switzerland.
Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland.
Nat Ecol Evol. 2023 Feb;7(2):198-204. doi: 10.1038/s41559-022-01946-1. Epub 2023 Jan 12.
Leaf phenology is key for regulating total growing-season mass and energy fluxes. Long-term temporal trends towards earlier leaf unfolding are observed across Northern Hemisphere forests. Phenological dates also vary between years, whereby end-of-season (EOS) dates correlate positively with start-of-season (SOS) dates and negatively with growing-season total net CO assimilation (A). These associations have been interpreted as the effect of a constrained leaf longevity or of premature carbon (C) sink saturation-with far-reaching consequences for long-term phenology projections under climate change and rising CO. Here, we use multidecadal ground and remote-sensing observations to show that the relationships between A and EOS are opposite at the interannual and the decadal time scales. A decadal trend towards later EOS persists in parallel with a trend towards increasing A-in spite of the negative A-EOS relationship at the interannual scale. This finding is robust against the use of diverse observations and models. Results indicate that acclimation of phenology has enabled plants to transcend a constrained leaf longevity or premature C sink saturation over the course of several decades, leading to a more effective use of available light and a sustained extension of the vegetation CO uptake season over time.
叶片物候是调节整个生长季物质和能量通量的关键。在整个北半球的森林中，叶片提前展开的长期时间趋势已经被观察到。物候日期也在不同年份之间变化，其中，生长季结束日期（EOS）与生长季开始日期（SOS）呈正相关，与生长季总净 CO 同化量（A）呈负相关。这些关联被解释为受限于叶片寿命或过早的碳（C）汇饱和的影响——这对气候变化和 CO 上升条件下的长期物候预测有深远的影响。在这里，我们使用了数十年的地面和遥感观测结果，表明在年际和十年际时间尺度上，A 与 EOS 之间的关系是相反的。尽管在年际尺度上 A-EOS 关系为负，但 EOS 的十年际趋势仍在朝着延迟的方向发展，同时 A 也呈上升趋势。这一发现不受不同观测和模型的影响。研究结果表明，物候的适应使植物在几十年的时间里超越了受限于叶片寿命或过早的 C 汇饱和的限制，从而更有效地利用可用的光，并随着时间的推移持续延长植被的 CO 吸收季节。
