Does the 14C method estimate net photosynthesis? II. Implications from cyclostat studies of marine phytoplankton

Authors

Shaofeng Pei, Qingdao Institute of Marine Geology
Edward A. Laws, Louisiana State University

Document Type

Article

Publication Date

1-1-2014

Abstract

Two species of marine phytoplankton, Isochrysis galbana and Chlorella kessleri, were grown in a continuous culture system on a 12-h:12-h light:dark cycle of illumination under nitrate-limited growth conditions. At growth rates of ~1d^-1, production rates estimated from ¹⁴C uptake were not significantly different from production rates estimated from changes in particulate organic carbon (POC) and total organic carbon (TOC). At growth rates of ~0.35d^-1, however, production rates based on uptake of ¹⁴C significantly (p<0.05) overestimated production rates based on changes in POC and TOC in all cases for C. kessleri and after 24h for I. galbana. The ratio of production based on ¹⁴C uptake to production based on changes in POC and TOC concentrations was in all cases higher after 24h than after 12h. The extent of overestimation after a 24-h incubation at ~0.35d^-1 was about 23 and 40% in the cases of I. galbana and C. kessleri, respectively. Dark respiration rates estimated from changes in ¹⁴C activity during the dark period were lower than the rates estimated from changes of POC and TOC concentrations during the 12h of darkness because only about 73% of the carbon respired during the dark period had been fixed during the previous 12-h photoperiod. The fact that the ¹⁴C method tends to overestimate net carbon assimilation by a greater percentage at low growth rates than at high growth rates probably reflects the greater efficiency of intracellular recycling of respired CO2 at high growth rates. The fact that the extent of overestimation is greater when cells are grown on a light:dark cycle probably reflects the fact that not all carbon respired in the dark was fixed during the previous photoperiod and that intracellular recycling of respired CO2 during the photoperiod is inefficient during some phases of the synchronized growth that tends to be entrained by light:dark cycles. © 2014 Elsevier Ltd.

Publication Source (Journal or Book title)

Deep Sea Research Part I Oceanographic Research Papers

First Page

94

Last Page

100

Recommended Citation

Pei, S., & Laws, E. (2014). Does the 14C method estimate net photosynthesis? II. Implications from cyclostat studies of marine phytoplankton. Deep Sea Research Part I Oceanographic Research Papers, 91, 94-100. https://doi.org/10.1016/j.dsr.2014.05.015