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Title: What drives the seasonality of photosynthesis across the Amazon basin? A cross-site analysis of eddy flux tower measurements from the Brasil flux network
Authors: Restrepo-Coupé, Natalia
Rocha, Humberto Ribeiro da
Hutyra, Lucy R.
Araujo, Alessandro C. da
Borma, Laura de Simone
Christoffersen, Bradley O.
Cabral, Osvaldo M.R.
Camargo, Plínio Barbosa de
Cardoso, Fernando Luiz
Costa, Antônio Carlos Lôla da
Fitzjarrald, David Roy
Goulden, Michael L.
Kruijt, Bart J.
Maia, Jair Max Furtunato
Malhi, Yadvinder Singh
Manzi, Antônio Ocimar
Miller, Scott Dennis
Nobre, Antônio Donato
Von Randow, Celso
Sá, Leonardo Deane Abreu
Sakai, Ricardo K.
Tóta, Júlio
Wofsy, Steven C.
Zanchi, Fabrício Berton
Saleska, Scott Reid
Keywords: Climate Change
Climate Effect
Ecosystem Modeling
Eddy Covariance
Forest Ecosystem
Land-use Change
Latent Heat Flux
Light Effect
Net Ecosystem Production
Solar Radiation
Tropical Forest
Amazon Basin
Issue Date: 2013
metadata.dc.publisher.journal: Agricultural and Forest Meteorology
metadata.dc.relation.ispartof: Volume 182-183, Pags. 128-144
Abstract: We investigated the seasonal patterns of Amazonian forest photosynthetic activity, and the effects thereon of variations in climate and land-use, by integrating data from a network of ground-based eddy flux towers in Brazil established as part of the 'Large-Scale Biosphere Atmosphere Experiment in Amazonia' project. We found that degree of water limitation, as indicated by the seasonality of the ratio of sensible to latent heat flux (Bowen ratio) predicts seasonal patterns of photosynthesis. In equatorial Amazonian forests (5° N-5° S), water limitation is absent, and photosynthetic fluxes (or gross ecosystem productivity, GEP) exhibit high or increasing levels of photosynthetic activity as the dry season progresses, likely a consequence of allocation to growth of new leaves. In contrast, forests along the southern flank of the Amazon, pastures converted from forest, and mixed forest-grass savanna, exhibit dry-season declines in GEP, consistent with increasing degrees of water limitation. Although previous work showed tropical ecosystem evapotranspiration (ET) is driven by incoming radiation, GEP observations reported here surprisingly show no or negative relationships with photosynthetically active radiation (PAR). Instead, GEP fluxes largely followed the phenology of canopy photosynthetic capacity (Pc), with only deviations from this primary pattern driven by variations in PAR. Estimates of leaf flush at three non-water limited equatorial forest sites peak in the dry season, in correlation with high dry season light levels. The higher photosynthetic capacity that follows persists into the wet season, driving high GEP that is out of phase with sunlight, explaining the negative observed relationship with sunlight. Overall, these patterns suggest that at sites where water is not limiting, light interacts with adaptive mechanisms to determine photosynthetic capacity indirectly through leaf flush and litterfall seasonality. These mechanisms are poorly represented in ecosystem models, and represent an important challenge to efforts to predict tropical forest responses to climatic variations. © 2013 Elsevier B.V.
metadata.dc.identifier.doi: 10.1016/j.agrformet.2013.04.031
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