title: Partitioning controls on Amazon forest photosynthesis between environmental and biotic factors at hourly to interannual timescales.
abstract: Gross ecosystem productivity (GEP) in tropical forests varies both with the environment and with biotic changes in photosynthetic infrastructure, but our understanding of the relative effects of these factors across timescales is limited. Here, we used a statistical model to partition the variability of seven years of eddy covariance-derived GEP in a central Amazon evergreen forest into two main causes: variation in environmental drivers (solar radiation, diffuse light fraction, and vapor pressure deficit) that interact with model parameters that govern photosynthesis and biotic variation in canopy photosynthetic light-use efficiency associated with changes in the parameters themselves. Our fitted model was able to explain most of the variability in GEP at hourly (R2= 0.77) to interannual (R2= 0.80) timescales. At hourly timescales, we found that 75% of observed GEP variability could be attributed to environmental variability. When aggregating GEP to the longer timescales (daily, monthly, and yearly), however, environmental variation explained progressively less GEP variability: At monthly timescales, it explained only 3%, much less than biotic variation in canopy photosynthetic light-use efficiency, which accounted for 63%. These results challenge modeling approaches that assume GEP is primarily controlled by the environment at both short and long timescales. Our approach distinguishing biotic from environmental variability can help to resolve debates about environmental limitations to tropical forest photosynthesis. For example, we found that biotically regulated canopy photosynthetic light-use efficiency (associated with leaf phenology) increased with sunlight during dry seasons (consistent with light but not water limitation of canopy development) but that realized GEP was nonetheless lower relative to its potential efficiency during dry than wet seasons (consistent with water limitation of photosynthesis in given assemblages of leaves). This work highlights the importance of accounting for differential regulation of GEP at different timescales and of identifying the underlying feedbacks and adaptive mechanisms.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana Champaign, Urbana, IL, 61801, USA.|National Center for Supercomputing Applications, University of Illinois at Urbana Champaign, Urbana, IL, 61801, USA.
authors.forename: Kaiyu
authors.initials: K
authors.lastname: Guan
authors.affiliation: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Hayek
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.|Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, NSW, Australia.
authors.forename: Natalia
authors.identifier: 0000-0003-3921-1772
authors.initials: N
authors.lastname: Restrepo-Coupe
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.|John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA.
authors.forename: Kenia T
authors.initials: KT
authors.lastname: Wiedemann
authors.affiliation: Department of Geosciences, Princeton University, Princeton, NJ, 80544, USA.
authors.forename: Xiangtao
authors.initials: X
authors.lastname: Xu
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Wehr
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.|Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM, USA.
authors.forename: Bradley O
authors.initials: BO
authors.lastname: Christoffersen
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana Champaign, Urbana, IL, 61801, USA.|Department of Forestry and Environmental Resources, North Carolina State University at Raleigh, Raleigh, NC, USA.
authors.forename: Guofang
authors.initials: G
authors.lastname: Miao
authors.affiliation: Department of Environmental Physics, University of Western Para-UFOPA, Para, Brazil.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: da Silva
authors.affiliation: Embrapa Amazonia Oriental, Belem, CEP 66095-100, Brasil.
authors.forename: Alessandro C
authors.initials: AC
authors.lastname: de Araujo
authors.affiliation: Embrapa Amazônia Oriental, Santarém, PA 68035-110, Brasil.
authors.forename: Raimundo C
authors.initials: RC
authors.lastname: Oliviera
authors.affiliation: Laboratorio de Ecologia Isotopica, Centro de Energia Nuclear na Agricultura (CENA), Universidade de Sao Paulo, Piracicaba, SP, 13400-970, Brasil.
authors.forename: Plinio B
authors.initials: PB
authors.lastname: Camargo
authors.affiliation: Department of Ecology and Evolutionary Biology and Laboratory of Tree Ring Research, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Russell K
authors.initials: RK
authors.lastname: Monson
authors.affiliation: Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, NSW, Australia.
authors.forename: Alfredo R
authors.initials: AR
authors.lastname: Huete
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Scott R
authors.initials: SR
authors.lastname: Saleska
mesh_terms: D017753:Ecosystem; D065928:Forests; D010788:Photosynthesis; D018515:Plant Leaves; D012621:Seasons; D014197:Trees
keywords: environmental limitation; leaf demography; leaf quality; leaf quantity; light-use efficiency; phenology; physiology; temperature sensitivity on productivity