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Measurement of planktonic CO 2 respiration in the light
Author(s) -
Carvalho Matheus C.,
Eyre Bradley D.
Publication year - 2012
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2012.10.167
Subject(s) - respiration , photosynthesis , irradiance , carbon cycle , oxygen , plankton , environmental science , primary production , carbon fibers , respiration rate , atmospheric sciences , total inorganic carbon , environmental chemistry , chemistry , carbon dioxide , ecology , botany , biology , physics , materials science , ecosystem , optics , organic chemistry , composite number , composite material
Respiration is an essential physiological process for all organisms and is a significant component of the global carbon cycle. However, CO 2 release rates in the light (CRR) by aquatic communities have seldom been measured directly; instead, the typical procedure is to measure oxygen consumption rates in the dark (OCR) and assume that they are approximately equivalent to CRR. Here we describe a method to measure CRR (and consequently gross photosynthesis rates) based on 13 C addition to incubation water in a closed system. We quantified planktonic CRR in situ in a lake, and also in laboratory experiments, where we tested the effects of temperature and irradiance on respiration rates. We also measured O 2 rates (respiration in the dark and net production in the light) to compare with those based on CO 2 , and found that in the lake, these rates were similar both for photosynthesis and respiration. In laboratory, however, they were very different, with CO 2 ‐based photosynthesis being higher, and CRR being lower than correspondent O 2 rates. These findings show that the usual approach of assuming similar OCR and CRR can be erroneous. We also found that higher temperature and irradiance caused higher CRR. The method was successful to provide CRR and photosynthetic measurements, but would greatly benefit from more precise techniques to measure the concentration of dissolved inorganic carbon in water.