Process-based estimates of terrestrial ecosystem isoprene emissions

Abstract

Abstract. In recent years evidence has emerged that the amount of isoprene emitted from a leaf is affected by the CO2 growth environment. Many – though not all – laboratory experiments indicate that emissions increase significantly at below-ambient CO2 concentrations and decrease when concentrations are raised to above ambient levels. A small number of process-based leaf isoprene emission models can reproduce this CO2-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 CO2 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. 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 CO2 concentration can be assessed. We show here for five model test sites that the suggested CO2-inhibition of leaf-isoprene metabolism can be large enough to offset increases in emissions due to CO2-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 CO2-isoprene inhibition may have the potential to significantly dampen the expected steep increase of ecosystem isoprene emission in a future warmer atmosphere with higher CO2 levels; this effect raises important questions for projections of future atmospheric chemistry and its connection to the terrestrial vegetation and carbon cycle.

Modelling exploration of the future of European beech (Fagus sylvatica L.) under climate change—Range, abundance, genetic diversity and adaptive response

“…Studies include evaluation of the modelled forest stand structure, development and tree species distributions (Smith et al, 2001;Hickler et al, 2004Hickler et al, , 2009Arneth et al, 2007;Koca et al, 2006), carbon cycling and productivity (Arneth et al, 2007;Hickler et al, 2008;Wramneby et al, 2008) and leaf area index .…”

Response of isoprene emission to ambient CO2 changes and implications for global budgets

“…Several studies have shown that elevated atmospheric CO 2 concentration inhibits isoprene production, as summarized by Arneth et al (2007b). This suggests a potential self‐regulation of isoprene emission in plants, where in a warmer climate, CO 2 ‐rich atmosphere emissions of isoprene remain relatively unperturbed.…”

Impact of climate change on tropospheric ozone and its global budgets

“…Thus, any future natural or anthropogenic land use change, such as the drying of the Amazon rain forest (Cox et al, 2004) or increase in crop growth, would have a large impact on the isoprene emission field. Furthermore, increases in atmospheric CO 2 may well decrease isoprene emission 384 G. Zeng et al: Climate change and tropospheric ozone ( Rosensteil et al, 2003;Arneth et al, 2007). Other climaterelated factors such as water availability, changes in the flux of photosynthetically active radiation (PAR), nutrient delivery and air pollution, will also effect isoprene and other biogenic emissions, either directly or through their impact on primary productivity.…”