Leaf ontogeny and demography explain photosynthetic seasonality in Amazon evergreen forests

Friday, 18 December 2015
Poster Hall (Moscone South)
Jin Wu1, Loren Albert1, Aline P Lopes2, Natalia Restrepo-Coupe3, Matthew Hayek4, Kenia T Wiedemann4, Kaiyu Guan5, Scott C Stark6, Neill Prohaska1, Julia V Tavares2, Suelen F Marostica2, Hideki Kobayashi7, Mauricio Lamano Ferreira8, Kleber Campos9, Rodrigo da Silva10, Paulo M Brando11, Dennis G Dye12, Travis E Huxman13, Alfredo R Huete14, Bruce W Nelson15 and Scott R Saleska1, (1)University of Arizona, Tucson, AZ, United States, (2)National Institute for Amazon Research (INPA), Manaus, AM, Brazil, (3)University of Technology Sydney, Ultimo, Australia, (4)Harvard University, Cambridge, MA, United States, (5)Stanford University, Stanford, CA, United States, (6)Michigan State University, East Lansing, MI, United States, (7)JAMSTEC, Yokohama, Japan, (8)Universidade de São Paulo, Centro de Energia Nuclear na Agricultura, Laboratório de Ecologia Isotópica, Piracicaba, Brazil, (9)University of Western Para-UFOPA, Department of Environmental Physics, Santarem, Brazil, (10)Federal University of Western Para, Santarem, Brazil, (11)Carnegie Institution for Science, Washington, DC, United States, (12)USGS Astrogeology Science Center, Flagstaff, AZ, United States, (13)University of California, Irvine, Irvine, CA, United States, (14)University of Technology Sydney, Plant Functional Biology and Climate Change, Ultimo, Australia, (15)INPA National Institute of Amazonian Research, Manaus, Brazil
Photosynthetic seasonality couples the evolutionary ecology of plant leaves to large-scale rhythms of carbon and water exchanges that are important feedbacks to climate. However, the extent, magnitude, and controls on photosynthetic seasonality of carbon-rich tropical forests are poorly resolved, controversial in the remote sensing literature, and inadequately represented in most earth system models. Here we show that ecosystem-scale phenology (measured by photosynthetic capacity), rather than environmental seasonality, is the primary driver of photosynthetic seasonality at four Amazon evergreen forests spanning gradients in rainfall seasonality, forest composition, and flux seasonality. We further demonstrate that leaf ontogeny and demography explain most of this ecosystem phenology at two central Amazon evergreen forests, using a simple leaf-cohort canopy model that integrates eddy covariance-derived CO2 fluxes, novel near-surface camera-detected leaf phenology, and ground observations of litterfall and leaf physiology. The coordination of new leaf growth and old leaf divestment (litterfall) during the dry season shifts canopy composition towards younger leaves with higher photosynthetic efficiency, driving large seasonal increases (~27%) in ecosystem photosynthetic capacity. Leaf ontogeny and demography thus reconciles disparate observations of forest seasonality from leaves to eddy flux towers to satellites. Strategic incorporation of such whole-plant coordination processes as phenology and ontogeny will improve ecological, evolutionary and earth system theories describing tropical forests structure and function, allowing more accurate representation of forest dynamics and feedbacks to climate in earth system models.