96
The Radiocarbon Method to Estimate Primary Production
tions of the same tissue homogenate (see above) are placed into the scintillation vials. Then 0.3 mllO% solution of NaOH is added into each of them, they
are closed with caps, and kept for 5 h at 80°C. Then the caps are taken out,
and vials are again kept at -90°C until they are dry. After cooling, 10% HCI
is added to them drop by drop until the evolution of COz from the sediment
at their bottom ceases. The samples thus hydrolyzed, if still too colored, can
then be bleached with the peroxides as described above, but after addition of
0.3ml 0.1N HCl.
In practice, also another alternative way for radioassay of the plant material was used - its quantitative combustion to COz (Wetzel 1964a,b, 1965;
Brylinski 1977; Adkin and Ho 1981). The dry plant material ground to powder
is combusted, applying the Van Slyke procedure or the specially adapted
CNH- analyzer with the use of hyamine or phenylethylamine solutions as
14COZ absorbers, for subsequent liquid scintillation counting. Some authors
have even radioassayed the COz formed by the combustion procedure, with
the aid of gas flow radiometers. At present, this technique can be recommended if the special automated and efficient combusting apparatus now produced commercially is available. Other combustion procedures are too slow.
When using this technique, it is also necessary to control the efficiency of combustion and of 14C recovery from the labeled organic matter. Significant losses
are very possible in this case, first of all, due to the incomplete combustion of
labeled organic matter. To control the efficiency of the transformation of 14C_
labeled organic carbon into 14COZ, the standard portion of nonlabeled plant
material is combusted together with a given amount of 14C_ labeled protein
hydrolyzate solution with known radioactivity. Then the radioactivity of 14COZ
thus formed and trapped (Rc) is measured by liquid scintillation under the
counting conditions used during the estimation of radioactivity in the initial
protein hydrolyzate solution (Rp). The counting efficiency K thus found (e.g.,
RjRp) can then be used to correct the radioassay results from routine estimations. It is also necessary the realize that the radioactivity of 14C-carbonate
working solution (Ri) must be determined under counting conditions equal to
those of the radioassay of the plant material after its combustion. This means
that it should be estimated in a counting sample containing the same amount
of COz - absorbing ammonium base solution as has been used to trap CO2•
The treatment of periphyton samples after incubation with 14C is somewhat different from the above descrition for macrophytes. Turfs of periphytonic overgrowth cover the solid surfaces in shallow areas of water basins, such
as rocks, stones, pebbles, molluskan shells, dead corals, and their debris. The
peryphytonic associations, besides filamentous algae and dwarf thallomic
macrophytes, contain also calcareous coralline red algae, small animals (accumulating carbonates) like forams, small mollusks, and calcareous tubificid
polychaetes. The periphytonic turfs also include abundant populations of heterotrophic (mostly filamentous) bacteria. These features of periphytonic associations determine a special approach to their treatment. As was also stated
above (Sect. 2.5.4), samples for experiments with periphytonic associations are
The Radiocarbon Method to Estimate Primary Production
tions of the same tissue homogenate (see above) are placed into the scintillation vials. Then 0.3 mllO% solution of NaOH is added into each of them, they
are closed with caps, and kept for 5 h at 80°C. Then the caps are taken out,
and vials are again kept at -90°C until they are dry. After cooling, 10% HCI
is added to them drop by drop until the evolution of COz from the sediment
at their bottom ceases. The samples thus hydrolyzed, if still too colored, can
then be bleached with the peroxides as described above, but after addition of
0.3ml 0.1N HCl.
In practice, also another alternative way for radioassay of the plant material was used - its quantitative combustion to COz (Wetzel 1964a,b, 1965;
Brylinski 1977; Adkin and Ho 1981). The dry plant material ground to powder
is combusted, applying the Van Slyke procedure or the specially adapted
CNH- analyzer with the use of hyamine or phenylethylamine solutions as
14COZ absorbers, for subsequent liquid scintillation counting. Some authors
have even radioassayed the COz formed by the combustion procedure, with
the aid of gas flow radiometers. At present, this technique can be recommended if the special automated and efficient combusting apparatus now produced commercially is available. Other combustion procedures are too slow.
When using this technique, it is also necessary to control the efficiency of combustion and of 14C recovery from the labeled organic matter. Significant losses
are very possible in this case, first of all, due to the incomplete combustion of
labeled organic matter. To control the efficiency of the transformation of 14C_
labeled organic carbon into 14COZ, the standard portion of nonlabeled plant
material is combusted together with a given amount of 14C_ labeled protein
hydrolyzate solution with known radioactivity. Then the radioactivity of 14COZ
thus formed and trapped (Rc) is measured by liquid scintillation under the
counting conditions used during the estimation of radioactivity in the initial
protein hydrolyzate solution (Rp). The counting efficiency K thus found (e.g.,
RjRp) can then be used to correct the radioassay results from routine estimations. It is also necessary the realize that the radioactivity of 14C-carbonate
working solution (Ri) must be determined under counting conditions equal to
those of the radioassay of the plant material after its combustion. This means
that it should be estimated in a counting sample containing the same amount
of COz - absorbing ammonium base solution as has been used to trap CO2•
The treatment of periphyton samples after incubation with 14C is somewhat different from the above descrition for macrophytes. Turfs of periphytonic overgrowth cover the solid surfaces in shallow areas of water basins, such
as rocks, stones, pebbles, molluskan shells, dead corals, and their debris. The
peryphytonic associations, besides filamentous algae and dwarf thallomic
macrophytes, contain also calcareous coralline red algae, small animals (accumulating carbonates) like forams, small mollusks, and calcareous tubificid
polychaetes. The periphytonic turfs also include abundant populations of heterotrophic (mostly filamentous) bacteria. These features of periphytonic associations determine a special approach to their treatment. As was also stated
above (Sect. 2.5.4), samples for experiments with periphytonic associations are