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GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 19, GB3006, doi:10.1029/2004GB002346, 2005

Contrasting responses of forest ecosystems to rising atmospheric CO₂: Implications for the global C cycle

E. H. DeLucia

Department of Plant Biology, University of Illinois, Urbana, Illinois, USA
Program in Ecology and Evolutionary Biology, University of Illinois, Urbana, Illinois, USA

D. J. Moore

Department of Plant Biology, University of Illinois, Urbana, Illinois, USA
Program in Ecology and Evolutionary Biology, University of Illinois, Urbana, Illinois, USA

R. J. Norby

Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA

Abstract

In two parallel but independent experiments, Free Air CO₂ Enrichment (FACE) technology was used to expose plots within contrasting evergreen loblolly pine (Pinus taeda L.) and deciduous sweetgum (Liquidambar styraciflua L.) forests to the level of CO₂ anticipated in 2050. Net primary production (NPP) and net ecosystem production (NEP) increased in both forests. In the year 2000, after exposing pine and sweetgum to elevated CO₂ for approximately 5 and 3 years, a complete budget calculation revealed increases in net ecosystem production (NEP) of 41% and 44% in the pine forest and sweetgum forest, respectively, representing the storage of an additional 174 gC m⁻² and 128 gC m⁻² in these forests. The stimulation of NPP without corresponding increases in leaf area index or light absorption in either forest resulted in 23–27% stimulation in radiation-use efficiency, defined as NPP per unit absorbed photosynthetically active radiation. Greater plant respiration contributed to lower NPP in the loblolly pine forest than in the sweetgum forest, and these forests responded differently to CO₂ enrichment. Where the pine forest added C primarily to long-lived woody tissues, exposure to elevated CO₂ caused a large increase in the production of labile fine roots in the sweetgum forest. Greater allocation to more labile tissues may cause more rapid cycling of C back to the atmosphere in the sweetgum forest compared to the pine forest. Imbalances in the N cycle may reduce the response of these forests to experimental exposure to elevated CO₂ in the future, but even at the current stimulation observed for these forests, the effect of changes in land use on C sequestration are likely to be larger than the effect of CO₂-induced growth stimulation.

Received 28 July 2004; accepted 8 April 2005; published 19 July 2005.

Keywords: forest productivity; carbon cycle; carbon dioxide; global change; mean residence time.

Index Terms: 0428 Biogeosciences: Carbon cycling (4806); 0439 Biogeosciences: Ecosystems, structure and dynamics (4815); 0414 Biogeosciences: Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912); 0426 Biogeosciences: Biosphere/atmosphere interactions (0315); 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions (0426, 1610).

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 224976 bytes)

Citation: DeLucia, E. H., D. J. Moore, and R. J. Norby (2005), Contrasting responses of forest ecosystems to rising atmospheric CO₂: Implications for the global C cycle, Global Biogeochem. Cycles, 19, GB3006, doi:10.1029/2004GB002346.

Copyright 2005 by the American Geophysical Union.