AOBPreview originally published online on January 7, 2008
Annals of Botany 2008 101(4):549-559; doi:10.1093/aob/mcm318
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A Simulation of the Importance of Length of Growing Season and Canopy Functional Properties on the Seasonal Gross Primary Production of Temperate Alpine Meadows
1 Laboratoire d'Ecologie Alpine, UMR 5553 UJF-CNRS, Université de Grenoble, BP53, 38041 Grenoble, France
2 Station Alpine J. Fourier, UMS 2925 UJF-CNRS, Université de Grenoble, BP53, 38041 Grenoble, France
* For correspondence. E-mail philippe.choler{at}ujf-grenoble.fr
Received: 1 October 2007 Returned for revision: 24 October 2007 Accepted: 20 November 2007 Published electronically: 8 January 2008
Background and Aims: Along snowmelt gradients, the canopies of temperate alpine meadows differ strongly in their structural and biochemical properties. Here, a study is made of the effects of these canopy dissimilarities combined with the snow-induced changes in length of growing season on seasonal gross primary production (GPP).
Methods: Leaf area index (LAI) and community-aggregated values of leaf angle and leaf nitrogen content were estimated for seven alpine plant canopies distributed along a marked snowmelt gradient, and these were used as input variables in a sun–shade canopy bulk-photosynthesis model. The model was validated for plant communities of early and late snowmelt sites by measuring the instantaneous CO2 fluxes with a canopy closed-chamber technique. A sensitivity analysis was conducted to estimate the relative impact of canopy properties and environmental factors on the daily and seasonal GPP.
Key Results: Carbon uptake was primarily related to the LAI and total canopy nitrogen content, but not to the leaf angle. For a given level of photosynthetically active radiation, CO2 assimilation was higher under overcast conditions. Sensitivity analysis revealed that increase of the length of the growing season had a higher effect on the seasonal GPP than a similar increase of any other factor. It was also found that the observed greater nitrogen content and larger LAI of canopies in late-snowmelt sites largely compensated for the negative impact of the reduced growing season.
Conclusions: The results emphasize the primary importance of snow-induced changes in length of growing season on carbon uptake in alpine temperate meadows. It was also demonstrated how using leaf-trait values of the dominants is a useful approach for modelling ecosystem carbon-cycle-related processes, particularly when continuous measurements of CO2 fluxes are technically difficult. The study thus represents an important step in addressing the challenge of using a plant functional-trait approach for biogeochemical modelling.
Key words: Alpine meadows, gross primary production, plant functional traits, snowmelt gradient, sun–shade model
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