International Institute for Earth System Science, Nanjing University, Nanjing, China.
Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing, China.
Nat Ecol Evol. 2019 Jul;3(7):1076-1085. doi: 10.1038/s41559-019-0931-1. Epub 2019 Jun 24.
Photosynthetic phenology has large effects on the land-atmosphere carbon exchange. Due to limited experimental assessments, a comprehensive understanding of the variations of photosynthetic phenology under future climate and its associated controlling factors is still missing, despite its high sensitivities to climate. Here, we develop an approach that uses cities as natural laboratories, since plants in urban areas are often exposed to higher temperatures and carbon dioxide (CO) concentrations, which reflect expected future environmental conditions. Using more than 880 urban-rural gradients across the Northern Hemisphere (≥30° N), combined with concurrent satellite retrievals of Sun-induced chlorophyll fluorescence (SIF) and atmospheric CO, we investigated the combined impacts of elevated CO and temperature on photosynthetic phenology at the large scale. The results showed that, under urban conditions of elevated CO and temperature, vegetation photosynthetic activity began earlier (-5.6 ± 0.7 d), peaked earlier (-4.9 ± 0.9 d) and ended later (4.6 ± 0.8 d) than in neighbouring rural areas, with a striking two- to fourfold higher climate sensitivity than greenness phenology. The earlier start and peak of season were sensitive to both the enhancements of CO and temperature, whereas the delayed end of season was mainly attributed to CO enrichments. We used these sensitivities to project phenology shifts under four Representative Concentration Pathway climate scenarios, predicting that vegetation will have prolonged photosynthetic seasons in the coming two decades. This observation-driven study indicates that realistic urban environments, together with SIF observations, provide a promising method for studying vegetation physiology under future climate change.
光合作用物候对陆地-大气碳交换有很大影响。由于实验评估有限，尽管光合作用物候对气候高度敏感，但人们仍然缺乏对未来气候下光合作用物候变化及其相关控制因素的综合认识。在这里，我们开发了一种利用城市作为自然实验室的方法，因为城市地区的植物通常暴露在更高的温度和二氧化碳（CO）浓度下，这反映了预期的未来环境条件。我们利用北半球超过 880 个城乡梯度（≥30°N），结合同时获取的太阳诱导叶绿素荧光（SIF）和大气 CO 的卫星反演数据，研究了大气 CO 和温度升高对大尺度光合作用物候的综合影响。结果表明，在城市 CO 和温度升高的条件下，植被光合作用活动开始得更早（-5.6±0.7 d），峰值更早（-4.9±0.9 d），结束得更晚（4.6±0.8 d），比邻近的农村地区高出 2 到 4 倍的气候敏感性。季节的提前开始和峰值对 CO 和温度的增强都很敏感，而季节的推迟结束主要归因于 CO 的富集。我们利用这些敏感性来预测四种代表性浓度路径气候情景下的物候变化，预测在未来二十年里，植被的光合作用季节将延长。这项基于观测的研究表明，现实的城市环境，加上 SIF 的观测，为研究未来气候变化下的植被生理学提供了一种很有前景的方法。
