HR: 08:30h
AN: B31E-03 INVITED    [Abstracts]
TI: A Global Assessment on the Effects of Incoming Diffuse Radiation on the Primary Productivity of Terrestrial Ecosystems
AU: * Cescatti, A
EM: alessandro.cescatti @ jrc.it
AF: European Commission - DG Joint Research Centre Institute for Environment and Sustainability, Via Fermi, Ispra, VA I-21020, Italy
AB: It is well known that an increase in the fraction of incoming radiation diffused by clouds or aerosol may enhance the light use efficiency (LEU) by generating a more uniform light distribution on the leaf area. An analysis of this effect at five Fluxnet sites has been published by Gu et al. (JGR, 2002), demonstrating the possibility to use flux measurements for the assessment of these phenomena at ecosystem scale. Despite the scientific relevance of this issue, a comprehensive assessment of the impact of the inter-annual variability in the incoming photosynthetic radiation (PAR) on the primary productivity is still missing. Such an analysis is needed to improve our understanding of the effect of aerosols and cloud cover on the spatial and temporal variability of the gross primary productivity (GPP). In addition, a better knowledge of the dependence of LUE on the composition of the incoming light is required to improve the parameterization of models based on satellite estimates of the fraction of absorbed PAR. The increasing availability of ecosystem carbon fluxes, together with direct measurements of incoming direct and diffuse PAR, allow an improvement of the analyses performed in the past, both in terms of ecosystem and spatial coverage and of scientific understanding. For this purpose the Fluxnet database has been used in order to perform a global analysis that covers about 200 sites and 900 year x site of flux measurements. The sensitivity of the different biomes at the diffuse fraction in the incoming PAR has been assessed by analyzing the variation of the ecosystem light response curves. Finally, the fraction of the inter-annual variability of GPP related to the variability of the direct/diffuse ratio has been estimated for the different biomes.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0321 Cloud/radiation interaction
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting