1Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 1, Tartu, 51014, Estonia
2Department of Ecology and Evolutionary Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309-0334, USA
3Division of Physical Geography and Ecosystem Analysis, Lund University, Sölvegatan 12, Lund, 22362, Sweden
4Istituto di Metodologie Chimiche del CNR, Area della Ricerca di Roma 1, Monterotondo Scalo, 00016, Italy
5Max Planck Institute for Chemistry, Biogeochemistry Department, Joh.-J.-Becher Weg 27, Mainz, 55128, Germany
6Federal Research Station Agroscope Reckenholz-Taenikon, ART, Zuerich, Switzerland
7Global Ecology Unit CSIC-CEAB-CREAF, Facultat de Ciències, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
8Centre d'Ecologie Fonctionnelle et Evolutive (CEFE-CNRS), 1919, Route de Mende, Montpellier cedex 5, 34293, France
Received: 09 Feb 2010 – Discussion started: 17 Feb 2010
Abstract. In models of plant volatile isoprenoid emissions, the instantaneous compound emission rate typically scales with the plant's emission potential under specified environmental conditions, also called as the emission factor, ES. In the most widely employed plant isoprenoid emission models, the algorithms developed by Guenther and colleagues (1991, 1993), instantaneous variation of the steady-state emission rate is described as the product of ES and light and temperature response functions. When these models are employed in the atmospheric chemistry modeling community, species-specific ES values and parameter values defining the instantaneous response curves are often taken as initially defined. In the current review, we argue that ES as a characteristic used in the models importantly depends on our understanding of which environmental factors affect isoprenoid emissions, and consequently need standardization during experimental ES determinations. In particular, there is now increasing consensus that in addition to variations in light and temperature, alterations in atmospheric and/or within-leaf CO2 concentrations may need to be included in the emission models. Furthermore, we demonstrate that for less volatile isoprenoids, mono- and sesquiterpenes, the emissions are often jointly controlled by the compound synthesis and volatility. Because of these combined biochemical and physico-chemical drivers, specification of ES as a constant value is incapable of describing instantaneous emissions within the sole assumptions of fluctuating light and temperature as used in the standard algorithms. The definition of ES also varies depending on the degree of aggregation of ES values in different parameterization schemes (leaf- vs. canopy- or region-scale, species vs. plant functional type levels) and various aggregated ES schemes are not compatible for different integration models. The summarized information collectively emphasizes the need to update model algorithms by including missing environmental and physico-chemical controls, and always to define ES within the proper context of model structure and spatial and temporal resolution.
Revised: 25 May 2010 – Accepted: 25 May 2010 – Published: 01 Jun 2010
Niinemets, Ü., Monson, R. K., Arneth, A., Ciccioli, P., Kesselmeier, J., Kuhn, U., Noe, S. M., Peñuelas, J., and Staudt, M.: The leaf-level emission factor of volatile isoprenoids: caveats, model algorithms, response shapes and scaling, Biogeosciences, 7, 1809-1832, doi:10.5194/bg-7-1809-2010, 2010.