Search

 

MediaMedia

Paris, 8 July 2010

Measuring photosynthesis : the Fluxnet network refines theoretical models

Using atmospheric flux measurements from the global Fluxnet network, an international team led by the Max Planck Institute, in which LSCE(1) (CEA-CNRS-UVSQ) is a participant, has managed to quantify more precisely the exchanges associated with the photosynthesis process at work in ecosystems. Researchers have worked out more precisely the respective contributions of each ecosystem to the total carbon fixed globally by vegetation. They have also established that on 40% of the planet's surfaces, ecosystems' capacity for photosynthesis is influenced mainly by precipitation, which is important information from the point of view of global warming.
The research has just been published in Science (Science Express) on 5 July 2010.

Photosynthesis is a key process in the global carbon cycle, enabling vegetation to absorb CO2 from the atmosphere to produce biomass. The process depends on three main factors: sunshine, temperature and precipitation (the amount of water in the soil). Scientists were looking at it both to better understand it and to try to anticipate any variations.

An international team led by the Max Planck Institute, in which LSCE is a participant, has just worked out a figure for total photosynthesis worldwide. To do this, it combined results from a set of theoretical models with results from a new model used to process the observations of the Fluxnet measurement network of 'flux towers'(2). Launched in 2000, this network enables the different laboratories involved to collect and pool flux data measured in different ecosystems throughout the world.

The researchers were therefore able to work out that total photosynthesis fixes 123 gigatonnes of carbon per year (GtC/year), with a margin for error of +/-8 GtC. This result is in line with previous estimates.
Above all, this study enabled them to establish more precisely the respective contributions of each ecosystem. Thus it appears that the contributions made to photosynthesis by temperate forests and prairies, for example in Europe, the United States and a large part of China, are less important than theoretical models predicted. Conversely, the contribution of cultivated areas and boreal forests, for example in Scandinavia and Siberia, is greater.
Researchers also established that on 40% of surfaces, photosynthesis is mainly influenced by precipitation. In other words, on these surfaces, the 'water stress' of vegetation has a predominant influence on capacity for photosynthesis. It also turns out to be the case that tropical areas are less sensitive to this than was previously thought, while temperate areas are more sensitive than expected.

These results show that, when it comes to the climate change expected in future, and particularly the rise in temperatures and resulting change in rainfall patterns, temperate ecosystems (including large cultivated areas) will be more vulnerable and tropical areas more robust than expected.

Notes:

(1) Climate and environmental sciences laboratory – LSCE/IPSL. View web site
(2) Flux towers are devices used to measure the flux of heat, water and CO2 between the Earth's surface and the atmosphere; the instruments are usually placed at the top of a flux tower, at the highest part of the forest (the canopy).

References:

View web site

Contact information:

Press contacts:

CNRS: Priscilla Dacher
Tel.: 01 44 96 46 06 - priscilla.dacher@cnrs-dir.fr

CEA: Stéphane Laveissière
Tel.: 01 64 50 27 53 - stephane.laveissiere@cea.fr

UVSQ: Robert Rivoire
Tel.: 01 39 25 78 63 - robert.rivoire@uvsq.fr

Top

Latest press releases

All disciplines

Back to homepageContactcredits