title: Forest productivity and water stress in Amazonia: observations from GOSAT chlorophyll fluorescence.
abstract: It is unclear to what extent seasonal water stress impacts on plant productivity over Amazonia. Using new Greenhouse gases Observing SATellite (GOSAT) satellite measurements of sun-induced chlorophyll fluorescence, we show that midday fluorescence varies with water availability, both of which decrease in the dry season over Amazonian regions with substantial dry season length, suggesting a parallel decrease in gross primary production (GPP). Using additional SeaWinds Scatterometer onboard QuikSCAT satellite measurements of canopy water content, we found a concomitant decrease in daily storage of canopy water content within branches and leaves during the dry season, supporting our conclusion. A large part (r(2) = 0.75) of the variance in observed monthly midday fluorescence from GOSAT is explained by water stress over moderately stressed evergreen forests over Amazonia, which is reproduced by model simulations that include a full physiological representation of photosynthesis and fluorescence. The strong relationship between GOSAT and model fluorescence (r(2) = 0.79) was obtained using a fixed leaf area index, indicating that GPP changes are more related to environmental conditions than chlorophyll contents. When the dry season extended to drought in 2010 over Amazonia, midday basin-wide GPP was reduced by 15 per cent compared with 2009.
authors.affiliation: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA. jung-eun.lee@jpl.nasa.gov
authors.forename: Jung-Eun
authors.initials: JE
authors.lastname: Lee
authors.forename: Christian
authors.initials: C
authors.lastname: Frankenberg
authors.forename: Christiaan
authors.initials: C
authors.lastname: van der Tol
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Berry
authors.forename: Luis
authors.initials: L
authors.lastname: Guanter
authors.forename: C Kevin
authors.initials: CK
authors.lastname: Boyce
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Fisher
authors.forename: Eric
authors.initials: E
authors.lastname: Morrow
authors.forename: John R
authors.initials: JR
authors.lastname: Worden
authors.forename: Salvi
authors.initials: S
authors.lastname: Asefi
authors.forename: Grayson
authors.initials: G
authors.lastname: Badgley
authors.forename: Sassan
authors.initials: S
authors.lastname: Saatchi
mesh_terms: D002734:Chlorophyll / Q000032:analysis* / Q000378:metabolism; D003681:Dehydration; D004784:Environmental Monitoring / Q000379:methods*; D005453:Fluorescence; D008954:Models, Biological; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology; D012621:Seasons; D013020:South America; D018531:Spacecraft; D013472:Sunlight; D014197:Trees / Q000502:physiology*; D014329:Tropical Climate
chemical_list: D002734:Chlorophyll
keywords: Amazon; chlorophyll fluorescence; drought; water stress