Use of the Radiocarbon Method to Determine Primary Production
77
The principle of the use of radiocarbon to measure photosynthetic incorporation of external CO2 into the biomass of hydrophytes remains the same
as described for phytoplankton (see Sect. 2.3.1). A portion of working solution 14C-bicarbonate (see Sect. 2.3.2.1) is injected into the volume of ambiental water contained in a glass jar or plastic chambers or an aquarium into which
have been placed examples of aquatic plants or their associations such the
periphytonic turfs or microphytobenthos, sampled together with undisturbed
sediment cores. After mixing, the charged vessels are incubated in situ or in
the laboratory under artificial illumination for 3-5 h. To estimate 14C incorporation due to processes other than photosynthesis, the same experiments are
performed in the dark. At the end of incubation, the plants are extracted from
the experimental vessels, and separated per specimen. After special treatment,
the plant material is prepared for radioassay with the aid of liquid scintillation counting. The estimated radioactivity is calculated per g-l dry weight of
the plant tissue material (R/). It is then corrected for dark 14C02 uptake by the
same plants (Rd), and thus the value of Rc is determined, corresponding to the
radioactivity of 14C incorporated photosynthetically into the tissues of plant
during its incubation on light: Rc = (R/- R d ) cpm mg- l . This latter value is used
to calculate the absolute rate of photosynthesis (Cp ): Cp = RcCr 1.061tmg C g-l
h- l , if Cr is the inverse specific radioactivity of inorganic (total CO2) carbon,
mg C cpm-l), t is the duration of incubation, hours, and 1.06 is the correction
coefficient on isotopic discrimination (see Sect. 2.3.1).
One of the two above basic parameters needed for calculation of photosynthesis rate, the inverse specific radioactivity of inorganic carbon of the carbonate system C" is extremely stable in time in natural waters, and especially
in the shallow areas of water basins where the experiments with benthic
hydrophytes are most often performed. It does not change to any extent in
water contained in open aquaria for many hours even if it is continually mixed
by a stirrer or in a of closed water circuit operated by a peristaltic pump. This
is a great advantage for this method in comparison with other methods for
measuring photosynthesis production in benthic hydrophytes. When using the
radiocarbon method, the experiments may be performed in situ or under simulated in situ conditions in open or closed vessels containing gas bubbles or
even containing the gas phase. This greatly facilitates the use of various versions of in situ experiments in various kinds of enclosures.
The types of experimental vessels for 14C experiments should be selected
taking into account these above feature of 14C-methodology - the high stability of Cr in most types of natural waters, and especially in shallow marine
waters, containing a high load of carbonate carbon (T CO2) and having a high
pH (8 to 10 in the day). For experimental estimation of primary production
by benthic plant associations in shallow bottom biotopes, two different strategies may be used. One is to measure the photosynthesis rates in individual
dominating hydrophytes per unit of their biomass, and then to calculate
primary production m- 2 of the bottom, when knowing their biomass in this
given area. The other is the direct measurement of photosynthesis rate in
whole-plant association, isolated during the experiment within an enclosure in
77
The principle of the use of radiocarbon to measure photosynthetic incorporation of external CO2 into the biomass of hydrophytes remains the same
as described for phytoplankton (see Sect. 2.3.1). A portion of working solution 14C-bicarbonate (see Sect. 2.3.2.1) is injected into the volume of ambiental water contained in a glass jar or plastic chambers or an aquarium into which
have been placed examples of aquatic plants or their associations such the
periphytonic turfs or microphytobenthos, sampled together with undisturbed
sediment cores. After mixing, the charged vessels are incubated in situ or in
the laboratory under artificial illumination for 3-5 h. To estimate 14C incorporation due to processes other than photosynthesis, the same experiments are
performed in the dark. At the end of incubation, the plants are extracted from
the experimental vessels, and separated per specimen. After special treatment,
the plant material is prepared for radioassay with the aid of liquid scintillation counting. The estimated radioactivity is calculated per g-l dry weight of
the plant tissue material (R/). It is then corrected for dark 14C02 uptake by the
same plants (Rd), and thus the value of Rc is determined, corresponding to the
radioactivity of 14C incorporated photosynthetically into the tissues of plant
during its incubation on light: Rc = (R/- R d ) cpm mg- l . This latter value is used
to calculate the absolute rate of photosynthesis (Cp ): Cp = RcCr 1.061tmg C g-l
h- l , if Cr is the inverse specific radioactivity of inorganic (total CO2) carbon,
mg C cpm-l), t is the duration of incubation, hours, and 1.06 is the correction
coefficient on isotopic discrimination (see Sect. 2.3.1).
One of the two above basic parameters needed for calculation of photosynthesis rate, the inverse specific radioactivity of inorganic carbon of the carbonate system C" is extremely stable in time in natural waters, and especially
in the shallow areas of water basins where the experiments with benthic
hydrophytes are most often performed. It does not change to any extent in
water contained in open aquaria for many hours even if it is continually mixed
by a stirrer or in a of closed water circuit operated by a peristaltic pump. This
is a great advantage for this method in comparison with other methods for
measuring photosynthesis production in benthic hydrophytes. When using the
radiocarbon method, the experiments may be performed in situ or under simulated in situ conditions in open or closed vessels containing gas bubbles or
even containing the gas phase. This greatly facilitates the use of various versions of in situ experiments in various kinds of enclosures.
The types of experimental vessels for 14C experiments should be selected
taking into account these above feature of 14C-methodology - the high stability of Cr in most types of natural waters, and especially in shallow marine
waters, containing a high load of carbonate carbon (T CO2) and having a high
pH (8 to 10 in the day). For experimental estimation of primary production
by benthic plant associations in shallow bottom biotopes, two different strategies may be used. One is to measure the photosynthesis rates in individual
dominating hydrophytes per unit of their biomass, and then to calculate
primary production m- 2 of the bottom, when knowing their biomass in this
given area. The other is the direct measurement of photosynthesis rate in
whole-plant association, isolated during the experiment within an enclosure in