Magnitude and regulation of bacterioplankton respiratory quotient across freshwater environmental gradients

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Magnitude and regulation of bacterioplankton respiratory quotient across freshwater environmental gradients. / Berggren, Martin; Lapierre, Jean-Francois; del Giorgio, Paul A.

I: The Isme Journal, Vol. 6, Nr. 5, 2012, s. 984-993.

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

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TY - JOUR

T1 - Magnitude and regulation of bacterioplankton respiratory quotient across freshwater environmental gradients

AU - Berggren, Martin

AU - Lapierre, Jean-Francois

AU - del Giorgio, Paul A.

PY - 2012

Y1 - 2012

N2 - Bacterioplankton respiration (BR) may represent the largest single sink of organic carbon in the biosphere and constitutes an important driver of atmospheric carbon dioxide (CO2) emissions from freshwaters. Complete understanding of BR is precluded by the fact that most studies need to assume a respiratory quotient (RQ; mole of CO2 produced per mole of O-2 consumed) to calculate rates of BR. Many studies have, without clear support, assumed a fixed RQ around 1. Here we present 72 direct measurements of bacterioplankton RQ that we carried out in epilimnetic samples of 52 freshwater sites in Quebec (Canada), using O-2 and CO2 optic sensors. The RQs tended to converge around 1.2, but showed large variability (s.d.=0.45) and significant correlations with major gradients of ecosystem-level, substrate-level and bacterial community-level characteristics. Experiments with natural bacterioplankton using different single substrates suggested that RQ is intimately linked to the elemental composition of the respired compounds. RQs were on average low in net autotrophic systems, where bacteria likely were utilizing mainly reduced substrates, whereas we found evidence that the dominance of highly oxidized substrates, for example, organic acids formed by photo-chemical processes, led to high RQ in the more heterotrophic systems. Further, we suggest that BR contributes to a substantially larger share of freshwater CO2 emissions than presently believed based on the assumption that RQ is similar to 1. Our study demonstrates that bacterioplankton RQ is not only a practical aspect of BR determination, but also a major ecosystem state variable that provides unique information about aquatic ecosystem functioning. The ISME Journal (2012) 6, 984-993; doi:10.1038/ismej.2011.157; published online 17 November 2011

AB - Bacterioplankton respiration (BR) may represent the largest single sink of organic carbon in the biosphere and constitutes an important driver of atmospheric carbon dioxide (CO2) emissions from freshwaters. Complete understanding of BR is precluded by the fact that most studies need to assume a respiratory quotient (RQ; mole of CO2 produced per mole of O-2 consumed) to calculate rates of BR. Many studies have, without clear support, assumed a fixed RQ around 1. Here we present 72 direct measurements of bacterioplankton RQ that we carried out in epilimnetic samples of 52 freshwater sites in Quebec (Canada), using O-2 and CO2 optic sensors. The RQs tended to converge around 1.2, but showed large variability (s.d.=0.45) and significant correlations with major gradients of ecosystem-level, substrate-level and bacterial community-level characteristics. Experiments with natural bacterioplankton using different single substrates suggested that RQ is intimately linked to the elemental composition of the respired compounds. RQs were on average low in net autotrophic systems, where bacteria likely were utilizing mainly reduced substrates, whereas we found evidence that the dominance of highly oxidized substrates, for example, organic acids formed by photo-chemical processes, led to high RQ in the more heterotrophic systems. Further, we suggest that BR contributes to a substantially larger share of freshwater CO2 emissions than presently believed based on the assumption that RQ is similar to 1. Our study demonstrates that bacterioplankton RQ is not only a practical aspect of BR determination, but also a major ecosystem state variable that provides unique information about aquatic ecosystem functioning. The ISME Journal (2012) 6, 984-993; doi:10.1038/ismej.2011.157; published online 17 November 2011

KW - DISSOLVED ORGANIC-MATTER

KW - CALCITE PRECIPITATION

KW - GROWTH EFFICIENCY

KW - CARBOXYLIC-ACIDS

KW - BACTERIAL-GROWTH

KW - LAKE ECOSYSTEMS

KW - CARBON

KW - METABOLISM

KW - CO2

KW - PHYTOPLANKTON

U2 - 10.1038/ismej.2011.157

DO - 10.1038/ismej.2011.157

M3 - Article

VL - 6

SP - 984

EP - 993

JO - ISME Journal

T2 - ISME Journal

JF - ISME Journal

SN - 1751-7362

IS - 5

ER -