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MCT-ELSA Résumé de rapport

Project ID: 509643
Financé au titre de: FP6-MOBILITY
Pays: Sweden

Final Activity Report Summary - MCT-ELSA (Marie Curie team on exchange processes in the land surface - Atmosphere System)

Vegetation and soil microorganisms play an important role in the regulation of atmospheric composition and climate. An illustrative example is the climate feedback through the terrestrial carbon cycle that has become the focus of attention in recent years: climate warming may lead to a reduced net terrestrial carbon uptake (the so-called carbon sink), hence a faster accumulation of fossil fuel CO2 in the atmosphere, hence to accelerated warming which reduces the terrestrial carbon sink even further. But what is more, an increasing number of studies suggest that a very tight coupling exists between the surface-atmosphere exchange of CO2 and that of (atmospherically) more reactive carbonaceous trace gases that also play a significant role in the climate system.

More specifically, terrestrial ecosystems emit a wide range of organic vapours (BVOC), a vast group of molecules with known (e.g. defence, attraction) or debated (e.g. range of possible stress-tolerances) functions in plants. Emissions of BVOC are strongly dependent on plant species. Not much is known yet about the spatial distribution of emission sources from groups of vegetation, and on what controls the emissions over periods from days to millennia. However, BVOCs (particularly the substances isoprene and monoterpenes) are crucial for vegetation-chemistry-climate interactions. Their oxidation products are important precursors for photochemical ozone production when levels of nitrogen oxides (NOx) are high. Conversely, in low NOx environment, ozone can react directly with BVOC and their reaction products, and so reduce ozone levels. A better understanding of the amount and seasonality of ecosystem BVOC emissions will also help to quantify their role for the production and growth of secondary organic aerosols or the possible contribution of their long-lived oxidation products to atmospheric chemistry when these are transported to remote regions.

The MCT-ELSA aimed to address some of the fundamental gaps in our understanding of the interactive processes which underpin BVOC and more inert trace gas fluxes, and their interactions with vegetation, greenhouse gas concentration and aerosol burden. The project combined field and modelling experiments, the former concentrating on northern high latitudes one of the most vulnerable regions to climate change.

Some of the key results of the project included:
(i) for the first time, identify isoprene emissions from important species of northern wetlands;
(ii) to develop a quantitative relationship for effects of short-term weather history as a crucial component of the abiotic factors that control BVOC emission pattern - in other words, plants emit (at the same temperature and light) relatively more isoprene after a period of a few warm days, compared to a period of cool days;
(iii) to demonstrate the effect of late summer leaf senescence reducing ecosystem BVOC fluxes significantly after the first light frost even when temperatures are still warm in the periods following the first frost;
(iv) to detect a very high temperature sensitivity of the leaf and ecosystem emission that appears to be much higher than in temperate or tropical plants;
(v) to detect unusual high growth rates of aerosol particles and air ions that opens the question how these interact with regional BVOC emission patterns;
(vi) to demonstrate, with a dynamic vegetation model, that laboratory-observed inhibition of leaf isoprene emissions by increasing atmospheric CO2 concentration offsets, in climate-warming scenarios, the stimulation of isoprene emissions in response to temperature;
(vii) to quantify the uncertainties associated with the 'traditional' versus 'direct CO2-effect-included' simulations of future isoprene emissions for projections of future ozone levels.


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