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Effects of temperature and irradiance on a benthic microalgal community: A combined two‐dimensional oxygen and fluorescence imaging approach
Author(s) -
Hancke Kasper,
Sorell Brian K.,
Lund-Hansen Lars Chresten,
Larsen Morten,
Hancke Torunn,
Glud Ronnie N.
Publication year - 2014
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2014.59.5.1599
Subject(s) - photosynthesis , irradiance , primary production , benthic zone , photosynthetically active radiation , chlorophyll a , chlorophyll fluorescence , heterotroph , oxygen , chemistry , atmospheric sciences , environmental science , botany , biology , ecology , physics , ecosystem , optics , genetics , organic chemistry , bacteria
The effects of temperature and light on both oxygen (O 2 ) production and gross photosynthesis were resolved in a benthic microalgal community by combining two‐dimensional (2D) imaging of O 2 and variable chlorophyll a (Chl a ) fluorescence. Images revealed a photosynthetically active community with spatial heterogeneity at the millimeter scale. Irradiance strongly increased pore‐water O 2 concentration, sediment net O 2 production, and gross photosynthesis. The latter was derived from measurements of the electron transfer rate (rETR) in Photosystem II. The onset of light saturation for gross photosynthesis was approximately twofold higher than for net O 2 production, reflecting significant light‐stimulated O 2 consumption at higher light (> 75 µmol photons m −2 s −1 ). Temperature stimulated O 2 consumption more than photosynthesis, turning the community more heterotrophic at elevated temperatures. Thus, the compensation irradiance (i.e., the irradiance at which community O 2 production and consumption balance) increased fivefold (from 6 to 30 µmol photons m −2 s −1 ) with a temperature increase from 10°C to 25°C, corresponding to a temperature coefficient (Q 10 ) of 2.9. Whereas net O 2 production had a temperature optimum at ∼ 20°C, no optimum was observed for gross photosynthesis within the investigated range (10°C to 25°C). The resolved 2D net O 2 production and rETR exhibited a significant exponential relationship, demonstrating predictable correlations between the net community production and gross photosynthesis for a complex microbial community, at different temperatures. The present imaging approach demonstrates a great potential to study consequences of environmental effects on photosynthetic activity and O 2 turnover in complex phototrophic benthic communities.