Process-based simulation of seasonality and drought stress in monoterpene emission models

Abstract

Abstract. Canopy emissions of volatile hydrocarbons such as isoprene and monoterpenes play an important role in air chemistry. They depend on various environmental conditions, are highly species-specific and are expected to be affected by global change. In order to estimate future emissions of these isoprenoids, differently complex models are available. However, seasonal dynamics driven by phenology, enzymatic activity, or drought stress strongly modify annual ecosystem emissions. Although these impacts depend themselves on environmental conditions, they have yet received little attention in mechanistic modelling.In this paper we propose the application of a mechanistic method for considering the seasonal dynamics of emission potential using the "Seasonal Isoprenoid synthase Model" (Lehning et al., 2001). We test this approach with three different models (GUENTHER, Guenther et al., 1993; NI-INEMETS, Niinemets et al., 2002a; BIM2, Grote et al., 2006) that are developed for simulating light-dependent monoterpene emission. We also suggest specific drought stress representations for each model. Additionally, the proposed model developments are compared with the approach realized in the MEGAN (Guenther et al., 2006) emission model. Models are applied to a Mediterranean Holm oak (Quercus ilex) site with measured weather data.The simulation results demonstrate that the consideration of a dynamic emission potential has a strong effect on annual monoterpene emission estimates. The investigated models, however, show different sensitivities to the procedure for determining this seasonality impact. Considering a drought impact reduced the differences between the applied models and decreased emissions at the investigation site by approxiCorrespondence to: R. Grote (ruediger.grote@imk.fzk.de) mately 33% on average over a 10 year period. Although this overall reduction was similar in all models, the sensitivity to weather conditions in specific years was different. We conclude that the proposed implementations of drought stress and internal seasonality strongly reduce estimated emissions and indicate the measurements that are needed to further evaluate the models.

The emission factor of volatile isoprenoids: stress, acclimation, and developmental responses

“…Recently, the effects of drought were empirically included in MEGAN, assuming an hypothetical relationship between soil water content and isoprene emission after a threshold soil water content is reached (Guenther et al, 2006). In other models, effects of drought are included through drought effects on C i , carbon metabolism and photosynthetic electron transport similarly to the C i -response function (Arneth et al, 2007b;Grote et al, 2006;Niinemets et al, 2002b; for comparison of approaches to model drought effects on emissions see also Grote et al, 2009Grote et al, , 2010. However, as drought response involves also a longer-term component, an approach linking E S to integrated drought dose, i.e., time-integrated plant water-status below the stress threshold water status, can provide a proxy to simulate such patterns similar to how past weather effects are included in the emission models (Sect.…”

Impacts of seasonal and regional variability in biogenic VOC emissions on surface ozone in the Pearl River delta region, China

“…The temperature was low and kept decreasing during the REA sampling period. Cool temperature can lead to a downregulation of isoprene emission (Petron et al, 2001), and the MEGAN algorithms may not adequately account for the influence of periods beyond the past 10 days (Grote et al, 2010).…”

Comparing three vegetation monoterpene emission models to measured gas concentrations with a model of meteorology, air chemistry and chemical transport

“…SIM-BIM calculates changes in the concentrations of a number of isoprene and monoterpene precursors within the chloroplast (Grote, 2007). It basically consists of a sequence of first-order Michaelis-Menten enzymatic reactions that depend on instantaneous temperature (Grote et al, 2010). Figure 1 presents an overview of the metabolic pathways in SIM-BIM, and Appendix A contains the corresponding equations, parameter values and abbreviations used for the chemicals and other variables.…”

“…Grote et al (2006) considered that SIM-BIM might overestimate emissions during the hottest season, potentially due to lower enzyme activities during drought periods. The estimation of emission amounts has uncertainties related to measurements, model structure and model parameters (Grote et al, 2010).…”

“…When IDP and DMADP come together to form the 10-carbon monoterpene backbone molecule GDP (geranyl diphosphate), a monoterpene is emitted. The potential production rates are determined by activities of isoprenoid biosynthesis-related enzymes (Grote et al, 2010).…”