Urban−rural gradients reveal joint control of elevated CO₂ and temperature on extended photosynthetic seasons
Wang, Songhan (Nanjing University. International Institute for Earth System Science)
Ju, Weimin (Nanjing University. International Institute for Earth System Science)
Peñuelas, Josep (Centre de Recerca Ecològica i d'Aplicacions Forestals)
Cescatti, Alessandro (European Commission, Joint Research Centre (Ispra, Itàlia))
Zhou, Yuyu (Iowa State University. Department of Geological and Atmospheric Sciences)
Fu, Yongshuo H.. (Beijing Normal University. College of Water Sciences)
Huete, Alfredo (University of Technology Sydney. School of Life Sciences)
Liu, Min (East China Normal University. School of Ecological and Environmental Sciences)
Zhang, Yongguang (Nanjing University. International Institute for Earth System Science)

Date:	2019
Abstract:	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 (CO₂) 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 CO₂, we investigated the combined impacts of elevated CO₂ and temperature on photosynthetic phenology at the large scale. The results showed that, under urban conditions of elevated CO2 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 CO₂ and temperature, whereas the delayed end of season was mainly attributed to CO₂ 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.
Grants:	European Commission 610028
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió acceptada per publicar
Subject:	Phenology
Published in:	Nature ecology & evolution, Vol. 3 (March 2019) , p. 1076-1085, ISSN 2397-334X

DOI: 10.1038/s41559-019-0931-1

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