Abstract ID: 702

What controls the seasonality of photosynthesis across the Amazon basin? A cross-site analysis of eddy flux tower measurements from the Brasil flux network

We investigated the seasonal and spatial patterns of Amazonian forest photosynthetic activity by integrating data from a network of ground-based eddy flux towers in Brazil established as part of the LBA project. We found that the pattern of photosynthesis at towers across the equatorial Amazon (5ºN-5ºS) shows little evidence of seasonal water limitation, as they sustain high or increasing levels of eddy-flux derived Gross Ecosystem Productivity (GEP) as the dry season progresses. By contrast, towers along the southern flank of the Amazon, in converted pasture sites, and in savanna, exhibit seasonal patterns consistent with varying degrees of water stress. Amazon ecosystem photosynthetic flux surprisingly showed no simple relationship with sunlight. We hypothesize that the seasonality of Amazon photosynthesis is controlled by the interaction of adaptive mechanisms (which biologically determine photosynthetic capacity through leaf flush and litter fall seasonality) and sunlight availability (which determines the fraction of photosynthetic capacity utilized). Equatorial climates advantage vegetation that can grow leaves in the dry season, when surface solar radiation peaks, but southerly sites may not because surface radiation there does not consistently peak in the dry season.

Session:  Carbon - The role of seasonality in carbon and water balance.

Presentation Type:  Oral