Technique of Measuring Phytoplankton Primary Production
27
6% more slowly than of the nonlabeled. This isotopic effect is accounted for
in calculations of photosynthesis rate measured with the aid of 14C (Steemann
Nielsen 1952; Sorokin 1960a).
To measure the rate of photosynthetic COz assimilation by phytoplankton, a portion of the working solution of labeled 14C-carbonate is added into
the sample of water. After its incubatiun unuer in situ (ur simulateu in siLU)
conditions, it is filtered through the membrane or glass fiber filter, which
retains the planktonic algae. The remains of labeled carbonate are removed
from the filters by special treatment. Then the filters are placed into the scintillation vial and the radioactivity of 14C-carbon assimilated by algae from the
14COz-carbonate pool is measured in them. The same procedure is carried out
with the sample exposed in dark. It is used then as dark control of 14COZ uptake
not connected with photosynthesis. Then the rate of photosynthesis in the
sample (Cp ) is calculated: Cp = (R[ - Rd)CrlTmg Cl- 1 h- l , if: R[ and R d- radioactivity of filters, correspondingly, from the light and dark bottles; the Cr value
in this formula is represented by the ratio C;lRc. C; is the total inorganic carbon
in the hydrocarbonate of the sample, mgCl- 1 , R; the radioactivity of the
working solution injected into the sample, cpm, and T is time of incubation in
hours.
2.3.2 Practical Use of the 14C-Method to Estimate Cps
The key points of 14C-methodology in this case are: preparation of the working
solution of labeled 14C-carbonate and estimation of its radioactivity (R;),
determination of total inorganic hydrocarbon ate carbon in water samples (C;),
selection of appropriate bottles for exposure of samples with 14C-label, duration and conditions of incubation, filtration procedure, estimation of radioactivity of filters (R[), corrections for 14C-assimilate losses during filtration and
for loss of radioactivity as respired COz, calculation of photosynthesis rates,
and control of 14C-estimations after the oxygen method.
2.3.2.1 Preparation of 14C-Carbonate Working Solution and Determination
of its Radioactivity (Ri)
The precision of primary production measurements largely depends upon the
quality of the working 14C-carbonate solution. The working solution should be
free of particles, colloids, or dissolved labeled organic matter. Batches of
ampules with a ready-for-use sterile working solution of labeled carbonate
destined specially for primary production estimations are supplied by some
companies manufacturing materials and instruments for work with radionuclides. In my practice I did not always find them convenient to use. The solu-
27
6% more slowly than of the nonlabeled. This isotopic effect is accounted for
in calculations of photosynthesis rate measured with the aid of 14C (Steemann
Nielsen 1952; Sorokin 1960a).
To measure the rate of photosynthetic COz assimilation by phytoplankton, a portion of the working solution of labeled 14C-carbonate is added into
the sample of water. After its incubatiun unuer in situ (ur simulateu in siLU)
conditions, it is filtered through the membrane or glass fiber filter, which
retains the planktonic algae. The remains of labeled carbonate are removed
from the filters by special treatment. Then the filters are placed into the scintillation vial and the radioactivity of 14C-carbon assimilated by algae from the
14COz-carbonate pool is measured in them. The same procedure is carried out
with the sample exposed in dark. It is used then as dark control of 14COZ uptake
not connected with photosynthesis. Then the rate of photosynthesis in the
sample (Cp ) is calculated: Cp = (R[ - Rd)CrlTmg Cl- 1 h- l , if: R[ and R d- radioactivity of filters, correspondingly, from the light and dark bottles; the Cr value
in this formula is represented by the ratio C;lRc. C; is the total inorganic carbon
in the hydrocarbonate of the sample, mgCl- 1 , R; the radioactivity of the
working solution injected into the sample, cpm, and T is time of incubation in
hours.
2.3.2 Practical Use of the 14C-Method to Estimate Cps
The key points of 14C-methodology in this case are: preparation of the working
solution of labeled 14C-carbonate and estimation of its radioactivity (R;),
determination of total inorganic hydrocarbon ate carbon in water samples (C;),
selection of appropriate bottles for exposure of samples with 14C-label, duration and conditions of incubation, filtration procedure, estimation of radioactivity of filters (R[), corrections for 14C-assimilate losses during filtration and
for loss of radioactivity as respired COz, calculation of photosynthesis rates,
and control of 14C-estimations after the oxygen method.
2.3.2.1 Preparation of 14C-Carbonate Working Solution and Determination
of its Radioactivity (Ri)
The precision of primary production measurements largely depends upon the
quality of the working 14C-carbonate solution. The working solution should be
free of particles, colloids, or dissolved labeled organic matter. Batches of
ampules with a ready-for-use sterile working solution of labeled carbonate
destined specially for primary production estimations are supplied by some
companies manufacturing materials and instruments for work with radionuclides. In my practice I did not always find them convenient to use. The solu-