Living Matter
85
1. Carbon
a) Living Matter
The complexities involved in the photosynthetic fixation of carbon
have already been briefly discussed. WICKMAN (1952) and CRAIG (1953)
were the first to demonstrate that marine plants (except phytoplankton)
are about 10%0 heavier in 13C than terrestrial plants. Recent investigations by SMITH and EpSTEIN (1971) have given a more detailed picture.
They subdivided the higher plants into two categories:
1) the bulk of the plant kingdom with low (j 13 C-values (- 24 to - 34%0),
2) the aquatics - desert and salt marsh plants and tropical grasses with a
relatively high 13C-content (- 6 to -19%0).
The algae have been put into a separate group with their b 13 C-variation range ( - 12 to - 23) lying intermediate between the ranges of the
two higher plant groups. The reasons for these differences are not well
understood, but as SMITH and EpSTEIN (1971) have shown, plants high in
13C differ from plants low in 13C in anatomy, physiology, biochemistry,
and ecology. Adaptations leading to high 13Cj 12 C ratios seem to be a
response to life under stress.
Animal tissues show the same range as their food supply. PARKER
(1964) has analyzed the most abundant biological samples in a shallow
marine bay and found that different members of the community had
isotopic compositions corresponding to every unit value of 13C between
- 6 and - 17%0, but that the 13C-content was constant for different individuals of the same species within ± 1%0.
DEGENS et al. (1968a) determined the carbon isotope composition of
marine phytoplankton cultures that were grown under defined conditions. Their data suggest that algae utilize molecular CO2 rather than
bicarbonate. If molecular CO2 is highly abundant and in isotopic equilibrium with bicarbonate, the difference between both components may
be as high as 28%0. The data of SACKETT et al. (1965), who observed that
plankton from arctic regions is depleted in 13C by about 6%0 relative to
plankton collected in tropical waters, can be reasonably interpreted as
showing that the molecular CO2 is depleted as temperature and metabolic rate rise.
DEGENS et al. (1968 b) have examined the carbon isotopic composition of the major biochemical constituents of marine plankton. Relative
to ocean water bicarbonate, the hemicellulose, the proteins, and the
pectins are enriched in 12C by about 17%0; cellulose and lignin, by 23%0;
and the extractable lipid fraction, by 30%0 (see Fig. 32).
The enrichment in 12C of lipids relative to total plant organic matter
has also been shown by SILVERMAN (1964), PARKER (1964), and others.
85
1. Carbon
a) Living Matter
The complexities involved in the photosynthetic fixation of carbon
have already been briefly discussed. WICKMAN (1952) and CRAIG (1953)
were the first to demonstrate that marine plants (except phytoplankton)
are about 10%0 heavier in 13C than terrestrial plants. Recent investigations by SMITH and EpSTEIN (1971) have given a more detailed picture.
They subdivided the higher plants into two categories:
1) the bulk of the plant kingdom with low (j 13 C-values (- 24 to - 34%0),
2) the aquatics - desert and salt marsh plants and tropical grasses with a
relatively high 13C-content (- 6 to -19%0).
The algae have been put into a separate group with their b 13 C-variation range ( - 12 to - 23) lying intermediate between the ranges of the
two higher plant groups. The reasons for these differences are not well
understood, but as SMITH and EpSTEIN (1971) have shown, plants high in
13C differ from plants low in 13C in anatomy, physiology, biochemistry,
and ecology. Adaptations leading to high 13Cj 12 C ratios seem to be a
response to life under stress.
Animal tissues show the same range as their food supply. PARKER
(1964) has analyzed the most abundant biological samples in a shallow
marine bay and found that different members of the community had
isotopic compositions corresponding to every unit value of 13C between
- 6 and - 17%0, but that the 13C-content was constant for different individuals of the same species within ± 1%0.
DEGENS et al. (1968a) determined the carbon isotope composition of
marine phytoplankton cultures that were grown under defined conditions. Their data suggest that algae utilize molecular CO2 rather than
bicarbonate. If molecular CO2 is highly abundant and in isotopic equilibrium with bicarbonate, the difference between both components may
be as high as 28%0. The data of SACKETT et al. (1965), who observed that
plankton from arctic regions is depleted in 13C by about 6%0 relative to
plankton collected in tropical waters, can be reasonably interpreted as
showing that the molecular CO2 is depleted as temperature and metabolic rate rise.
DEGENS et al. (1968 b) have examined the carbon isotopic composition of the major biochemical constituents of marine plankton. Relative
to ocean water bicarbonate, the hemicellulose, the proteins, and the
pectins are enriched in 12C by about 17%0; cellulose and lignin, by 23%0;
and the extractable lipid fraction, by 30%0 (see Fig. 32).
The enrichment in 12C of lipids relative to total plant organic matter
has also been shown by SILVERMAN (1964), PARKER (1964), and others.