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High light intensity mediates a shift from allochthonous to autochthonous carbon use in phototrophic stream biofilms
Author(s) -
Wagner Karoline,
Bengtsson Mia M.,
Findlay Robert H.,
Battin Tom J.,
Ulseth Amber J.
Publication year - 2017
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1002/2016jg003727
Subject(s) - benthic zone , dissolved organic carbon , light intensity , biofilm , urban stream , phototroph , diel vertical migration , carbon cycle , environmental chemistry , riparian zone , ecology , environmental science , biology , chemistry , photosynthesis , ecosystem , botany , water quality , habitat , bacteria , physics , genetics , optics
Changes in the riparian vegetation along stream channels, diurnal light availability, and longitudinal fluctuations in the local light regime in streams influence primary production and carbon (C) cycling in benthic stream biofilms. To investigate the influence of light availability on the uptake dynamics of autochthonous and allochthonous dissolved organic carbon (DOC) in benthic biofilms, we experimentally added 13 C‐labeled allochthonous DOC to biofilms grown under light intensities ranging from 5 to 152 μmol photons m −2 s −1 . We calculated the net C flux, which showed that benthic biofilms released autochthonous DOC across the entire light gradient. Light availability and diurnal light patterns influenced C uptake by benthic biofilms. More allochthonous DOC was respired under low light availability and at night, whereas under high light availability and during the day mainly autochthonous C was respired by the benthic biofilm community. Furthermore, phenol oxidase activity (indicative of allochthonous DOC uptake) was more elevated under low light availability, whereas beta‐glucosidase activity (indicative of autochthonous DOC use) increased with light intensity. Collectively, our results suggest that biofilms exposed to high light inputs preferentially used autochthonous DOC, whereas biofilms incubated at attenuated levels showed greater use of allochthonous DOC. This has implications for the spatial dynamics of DOC uptake in streams and speaks against the occurrence of priming effects in algal‐dominated stream biofilms.