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Effect of smoke on subcanopy shaded light, canopy temperature, and carbon dioxide uptake in an Amazon rainforest
Author(s) -
Doughty Christopher E.,
Flanner Mark G.,
Goulden Michael L.
Publication year - 2010
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2009gb003670
Subject(s) - canopy , environmental science , atmospheric sciences , eddy covariance , carbon dioxide , irradiance , ecosystem , ecology , geology , biology , physics , quantum mechanics
Daytime Net Ecosystem CO 2 uptake (NEE) in an Amazon forest has been shown to increase significantly during smoky periods associated with biomass burning. We investigated whether the increase in CO 2 uptake is caused by increased irradiance in the lower canopy, which results from increased above‐canopy diffuse light, or by decreased canopy temperature, which results from decreased above‐canopy net radiation. We used Sun photometers measuring aerosol optical depth to find nonsmoky (Aerosol Optical Depth (AOT) < 0.35), smoky (AOT > 0.5) and very smoky (AOT > 0.7) periods for the Tapajos region in the Amazon. Using a network of subcanopy photosynthetic photon flux density (PPFD) sensors, we detected a ∼4 μ mol m −2 s −1 increase in subcanopy diffuse light during smoky periods relative to nonsmoky periods. Using a pyrgeometer to measure upwelling longwave radiation and, hence, canopy surface temperature, we found a ∼0.5°C cooling relative to air temperature during smoky periods. We modeled subcanopy irradiance based on the subcanopy PPFD sensors and combined this with subcanopy leaf photosynthesis measurements to determine how the increased lower canopy light affected NEE. We used the relationship between temperature and NEE measured by eddy covariance to determine the effect of decreased canopy temperature on canopy CO 2 uptake. We found that the increase in CO 2 uptake at high aerosol optical depths is primarily a result of increased shaded light in the subcanopy (accounting for ∼80%) and to a lesser extent the effect of decreased canopy temperature (accounting for ∼20%).