ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-6-8011-2006 Process-based estimates of terrestrial ecosystem isoprene emissions Arneth A. 1 Niinemets Ü. 2 3 Pressley S. 4 Bäck J. 5 Hari P. 5 Karl T. 6 Noe S. 2 Prentice I. C. 7 Serça D. 8 Hickler T. 1 Wolf A. 9 Smith B. 1 Department of Physical Geography and Ecosystems Analysis, Centre for GeoBiosphere Science, Lund University Sölvegatan 12, 223 62, Lund, Sweden Department of Plant Physiology, Institute of Molecular and Cell Biology, University of Tartu, Riia 23, Tartu Estonia Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 64, Tartu 51014, Estonia Washington State University, Department of Civil and Environmental Engineering, USA Department of Forest Ecology, University of Helsinki, Finland Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA QUEST, Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK Laboratoire d’Aerologie, Toulouse, France Forest Ecology, ETH Zuerich, Switzerland 23 08 2006 6 4 8011 8068 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/6/8011/2006/acpd-6-8011-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/6/8011/2006/acpd-6-8011-2006.pdf

In recent years evidence has emerged that the amount of isoprene emitted from a leaf is affected by the CO<sub>2</sub> growth environment. Many &ndash; though not all &ndash; laboratory experiments indicate that emissions increase significantly at below-ambient CO<sub>2</sub> concentrations and decrease when concentrations are raised to above ambient levels. A small number of process-based leaf isoprene emission models can reproduce this CO<sub>2</sub>-stimulation and -inhibition. These models are briefly reviewed, and their performance in standard conditions compared with each other and to an empirical algorithm. One of the models was judged particularly useful to be incorporated into a dynamic vegetation model framework, LPJ-GUESS, aiming to develop a tool that allows the interactive effects of climate and increasing CO<sub>2</sub> concentration on vegetation distribution, productivity, and leaf and ecosystem isoprene emissions to be explored. The coupled vegetation dynamics-isoprene model is described and used here in a mode particularly suited for the ecosystem scale, but it can be employed at the global level as well. <br><br> Annual and/or daily isoprene emissions simulated by the model were evaluated against flux measurements (or model estimates that had previously been evaluated with flux data) from a wide range of environments, and agreement between modelled and simulated values was generally good. By using a dynamic vegetation model, effects of canopy composition, disturbance history, or trends in CO<sub>2</sub> concentration can be assessed. We show here for five model test sites that the suggested CO<sub>2</sub>-inhibition of leaf-isoprene metabolism can be large enough to offset increases in emissions due to CO<sub>2</sub>-stimulation of vegetation productivity and leaf area growth. When effects of climate change are considered atop the effects of atmospheric composition the interactions between the relevant processes will become even more complex. The CO<sub>2</sub>-isoprene inhibition may have the potential to significantly dampen the expected steep increase of ecosystem isoprene emission in a future warmer atmosphere with higher CO<sub>2</sub> levels; this effect raises important questions for projections of future atmospheric chemistry and its connection to the terrestrial vegetation and carbon cycle.