Future atmospheric CO2 leads to delayed autumnal senescence

doi:10.1111/j.1365-2486.2007.01473.x

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Wiley InterScience

Global Change Biology

Volume 14 Issue 2, Pages 264 - 275

Published Online: 29 Oct 2007

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Future atmospheric CO₂ leads to delayed autumnal senescence

GAIL TAYLOR ^* ¹ , MATTHEW J. TALLIS ^* ¹ , CHRISTIAN P. GIARDINA†, KEVIN E. PERCY‡, FRANCO MIGLIETTA§, POOJA S. GUPTA¶, BENIAMINO GIOLI§, CARLO CALFAPIETRA∥^**, BIRGIT GIELEN††, MARK E. KUBISKE‡‡, GIUSEPPE E. SCARASCIA-MUGNOZZA∥^**, KATRE KETS§§, STEPHEN P. LONG¶¶ and DAVID F. KARNOSKY¶

^* School of Biological Sciences, University of Southampton, Bassett Crescent East, S016 7PX, UK, †North Central Research Station, USDA Forest Service, Houghton, Michigan 49931-1295 USA, ‡Natural Resources Canada, Canadian Forest Service-Atlantic Forestry Centre, PO Box 4000, Fredericton, NB, Canada E3B 5P7, §Institute of Biometeorology-CNR, Via Caproni, 8 50145 Firenze, Italy, ¶School of Forest Resources & Environmental Science, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA, ∥Department of Forest Environment and Resources (DISAFRI), University of Tuscia, Via S. Camillo De Lellis, Viterbo 01100, Italy, ^** Institute of Agro-Environmental & Forest Biology (IBAF), National Research Council (CNR), Via Salaria km 29, 300, 00016 Monterotondo Scalo, Roma, Italy, ††Research Group of Plant and Vegetation Ecology, Department of Biology, University of Antwerp, Campus Drie Eiken, Universiteitsplein 1, Wilrijk B-2610, Belgium, ‡‡Forestry Sciences Lab, North Central Research Station, USDA Forest Service, 5985 Highway K, Rhinelander, WI 54501 USA, §§Institute of Botany & Ecology, University of Tartu, 40 Lai Str, 51005 Tartu, Estonia, ¶¶190 Edward R. Madigan Laboratory, Departments of Plant Biology, University of IL at Urbana, 1201 West Gregory Drive, Champaign, Illinois 61801-4798, USA

Correspondence: Gail Taylor, e-mail: G.Taylor@soton.ac.uk

¹These authors contributed equally to this work.

KEYWORDS

autumnal phenology • elevated CO₂ • FACE • LAI • Populus • senescence

ABSTRACT

Growing seasons are getting longer, a phenomenon partially explained by increasing global temperatures. Recent reports suggest that a strong correlation exists between warming and advances in spring phenology but that a weaker correlation is evident between warming and autumnal events implying that other factors may be influencing the timing of autumnal phenology. Using freely rooted, field-grown Populus in two Free Air CO₂ Enrichment Experiments (AspenFACE and PopFACE), we present evidence from two continents and over 2 years that increasing atmospheric CO₂ acts directly to delay autumnal leaf coloration and leaf fall. In an atmosphere enriched in CO₂ (by ∼45% of the current atmospheric concentration to 550 ppm) the end of season decline in canopy normalized difference vegetation index (NDVI) – a commonly used global index for vegetation greenness – was significantly delayed, indicating a greener autumnal canopy, relative to that in ambient CO₂. This was supported by a significant delay in the decline of autumnal canopy leaf area index in elevated as compared with ambient CO₂, and a significantly smaller decline in end of season leaf chlorophyll content. Leaf level photosynthetic activity and carbon uptake in elevated CO₂ during the senescence period was also enhanced compared with ambient CO₂. The findings reveal a direct effect of rising atmospheric CO₂, independent of temperature in delaying autumnal senescence for Populus, an important deciduous forest tree with implications for forest productivity and adaptation to a future high CO₂ world.