Use of the Radiocarbon Method to Determine Primary Production
91
the clamp is closed again. The isotopic solution (10ml, see above Sect. 2.5.3)
is injected into the vessel through the serum plug. The water column inside
the vessel is instantly thoroughly mixed with the aid of a manual propeller
(Fig. 2.20). Then with a 50-ml syringe though the same serum plug, a sample
of water is taken for Cr analysis. This operation is repeated before the end of
incubation.
c) Estimating the dependence of in situ photosynthesis rates on light attenuation in hydrophytes inhabiting slope biotopes
These estimations are important to evaluate primary production of benthic
plant associations which inhabit slope areas. The main factors controlling their
primary production are light attenuation down the slope and light adaptation
of the hydrophytes (Marsh 1970; Littler 1973; Wanders 1976; Titlyanov et al.
1987). The appropriate experiments can by carried out be incubation with
14C-carbonate of the plants in situ at their place of collection along the slope,
starting from the coast down to the dark. The incubations should be started
simultaneously or within short time intervals, and be conducted at about the
same period of the light day. To meet the latter condition, the experiment must
be organized as follows: along the slope, a cross-section rope should be
extended. The diver selects some five to seven sites from the upper slope edge
down to the depth at which the illumination is 1-2% PAR, and marks them.
Then, at these sites, 2-3-1 open glass jars are fixed at the bottom. Into each jar
are placed plant specimens of the same species and approximately of equal
size, collected in the vicinity of a given mark where a corresponding jar is fixed.
This should be carried out during the afternoon. The jars with plant specimens
inside them are left open overnight. Early in the morning the diver, supplied
with vials each containing 10ml of diluted 14C working solution and with lids
to close the jars, dives along the cross-section. Near each of the marks he finds
the jar, closes it with a lid, injects the radioisotopic solution into it through the
serum plug in the lid, and instantly mixes water in the jar with the aid of a
hand-operating propeller (Fig. 2.20). Then he records the exact time of isotope
injection and moves rapidly to the next mark to inject the following jar. The
whole operation should not take more than half an hour. After exposure
for 4-5h (for example from 07.00h till midday) the diver stops the incubation
by taking out the plant examples from the jars and inserting them into black
bags.
There is also another, simpler, way to conduct this kind of experiment,
which is based on the transferred - in situ approach. Specimens of plants are
collected along the cross-section near the marks into separate bags. This should
be done in the late afternoon to avoid exposure of deep-living plant specimens
to strong light. The specimens thus collected should be kept overnight in open
plastic bags immersed in the aquarium, as shown in Fig. 2.22. Early in the
morning, the specimens from corresponding depths are placed into separate
jars filled with pre filtered water. One extra jar with a plant specimen inside
will serve as dark control. All the jars thus arranged are transported by boat
91
the clamp is closed again. The isotopic solution (10ml, see above Sect. 2.5.3)
is injected into the vessel through the serum plug. The water column inside
the vessel is instantly thoroughly mixed with the aid of a manual propeller
(Fig. 2.20). Then with a 50-ml syringe though the same serum plug, a sample
of water is taken for Cr analysis. This operation is repeated before the end of
incubation.
c) Estimating the dependence of in situ photosynthesis rates on light attenuation in hydrophytes inhabiting slope biotopes
These estimations are important to evaluate primary production of benthic
plant associations which inhabit slope areas. The main factors controlling their
primary production are light attenuation down the slope and light adaptation
of the hydrophytes (Marsh 1970; Littler 1973; Wanders 1976; Titlyanov et al.
1987). The appropriate experiments can by carried out be incubation with
14C-carbonate of the plants in situ at their place of collection along the slope,
starting from the coast down to the dark. The incubations should be started
simultaneously or within short time intervals, and be conducted at about the
same period of the light day. To meet the latter condition, the experiment must
be organized as follows: along the slope, a cross-section rope should be
extended. The diver selects some five to seven sites from the upper slope edge
down to the depth at which the illumination is 1-2% PAR, and marks them.
Then, at these sites, 2-3-1 open glass jars are fixed at the bottom. Into each jar
are placed plant specimens of the same species and approximately of equal
size, collected in the vicinity of a given mark where a corresponding jar is fixed.
This should be carried out during the afternoon. The jars with plant specimens
inside them are left open overnight. Early in the morning the diver, supplied
with vials each containing 10ml of diluted 14C working solution and with lids
to close the jars, dives along the cross-section. Near each of the marks he finds
the jar, closes it with a lid, injects the radioisotopic solution into it through the
serum plug in the lid, and instantly mixes water in the jar with the aid of a
hand-operating propeller (Fig. 2.20). Then he records the exact time of isotope
injection and moves rapidly to the next mark to inject the following jar. The
whole operation should not take more than half an hour. After exposure
for 4-5h (for example from 07.00h till midday) the diver stops the incubation
by taking out the plant examples from the jars and inserting them into black
bags.
There is also another, simpler, way to conduct this kind of experiment,
which is based on the transferred - in situ approach. Specimens of plants are
collected along the cross-section near the marks into separate bags. This should
be done in the late afternoon to avoid exposure of deep-living plant specimens
to strong light. The specimens thus collected should be kept overnight in open
plastic bags immersed in the aquarium, as shown in Fig. 2.22. Early in the
morning, the specimens from corresponding depths are placed into separate
jars filled with pre filtered water. One extra jar with a plant specimen inside
will serve as dark control. All the jars thus arranged are transported by boat