Abstract
Plankton respiration rate is a major component of global CO2 production and is forecasted to increase rapidly in the Arctic with warming. Yet, existing assessments in the Arctic evaluated plankton respiration in the dark. Evidence that plankton respiration may be stimulated in the light is particularly relevant for the high Arctic where plankton communities experience continuous daylight in spring and summer. Here we demonstrate that plankton community respiration evaluated under the continuous daylight conditions present in situ, tends to be higher than that evaluated in the dark. The ratio between community respiration measured in the light (Rlight) and in the dark (Rdark) increased as the 2/3 power of Rlight so that the Rlight:Rdark ratio increased from an average value of 1.37 at the median Rlight measured here (3.62 µmol O2 L−1 d−1) to an average value of 17.56 at the highest Rlight measured here (15.8 µmol O2 L−1 d−1). The role of respiratory processes as a source of CO2 in the Arctic has, therefore, been underestimated and is far more important than previously believed, particularly in the late spring, with 24 h photoperiods, when community respiration rates are highest.
Highlights
Community respiration is the process responsible for the degradation of organic matter by organisms to extract energy to support biological processes in the ecosystem and provides, an integrated assessment of the energy requirements of the ecosystem[1]
Mean monthly community respiration rates in the Svalbard region were highest in April and lowest in August (Fig. 1), these differences were only significant for respiration rates measured in the light (Kruskal-Wallis test, P = 0.013), when rates measured in August were significantly lower than those measured in April and May (Dunn’s test, P < 0.05), but not June (Dunn’s test, P = 0.27)
The fitted regression equation showed that the ratio respiration in the light (Rlight):respiration in the dark (Rdark) was scaled to the 2/3 power of Rlight (Fig. 3B), so that the Rlight and Rdark were similar for Rlight of the order of 1 μmol O2 L−1 d−1, but Rlight was four-fold greater than Rdark for high Rlight rates of the order of 10 μmol O2 L−1 d−1 (Fig. 3B)
Summary
Community respiration is the process responsible for the degradation of organic matter by organisms to extract energy to support biological processes in the ecosystem and provides, an integrated assessment of the energy requirements of the ecosystem[1]. The severity of the bias involved in the assumption that community respiration in the dark equals that in the light involved in most estimates of plankton community respiration, depends on the photoperiod the community experiences. This shows the broadest range in the high Arctic, where there is an extended period of darkness in fall and winter, where darkness prevails, and an extended period of continuous daylight in spring and summer, when any differences between respiration in the dark and that in the light will have the highest impact on the www.nature.com/scientificreports/. We did so by calculating respiration rate using oxygen consumption in the dark, evaluated by high-precision Winkler titration, and estimating community respiration in the light as the difference between gross primary production (GPP18O), evaluated with the 18O method and net community production (NCP), evaluated from bulk oxygen mass balance, of communities incubated under ambient incoming irradiance
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