Respiration: comparison of the Winkler technique, O2 electrodes, O2 optodes and the respiratory electron transport system assay

Abstract

Aerobic respiration is a biological energy generation process that consumes organic carbon and oxygen. In the ocean, the balance between photosynthesis and respiration is recognized as critical to understanding the ocean’s impact on the hydrospheric and atmospheric CO2. Techniques to determine respiration can be based on inorganic chemistry, electrochemistry, photochemistry, and enzymology. Here, for method comparison, physiological respiration was simultaneously measured by the Winkler method (W), O2 electrodes (E), and O2 optodes (O). These techniques detected respiratory O2 consumption (R), in situ, in dark incubation chambers. Respiratory electron transport system activity measurements detected potential respiration (Ф), biochemically. Leptomysis lingvura, a marine mysid, and Ulva rigida, a species of green algal sea lettuce, were the two organisms tested. Physiological respiration results from each technique were not statistically significantly different (multiple paired Student’s t tests, p value > 0.05) and were inside the range of similar published measurements. The mean dry-mass-specific respiration in L. lingvura and U. rigida was 0.147 ± 0.037 and 0.023 ± 0.008 µmol O2 h−1 (mg dry mass)−1, n = 9, respectively. The R-to-Ф ratios were different in the two organisms. However, linear regression between R and Ф for L. lingvura and U. rigida was stronger (r 2 = 0.814 and 0.313) than the linear regression between R and dry biomass (r 2 = 0.643 and 0.213). The application of Passing–Bablok regression analysis evidenced the high correlation between the results, and the Bland–Altman analysis examined the average difference (“bias”) and limits of agreement between the methods.