600
K. M. G. Mostofa et al.
δ 13 C value in the phytoplankton bloom season suggests that phytoplankton photosynthesis may be limited by CO 2 depletion (Takahashi et al. 1990). It has been
observed that aqueous CO 2 , [CO 2 ] aq , determined in freshwater and marine waters
is relatively low (0.13–35 M) in freshwater and relatively higher (5–120 M)
in seawater (Fogel et al. 1992; Francois et al. 1993; Yoshioka 1997; Takahashi
et al. 1990; Herczeg and Fairbanks 1987). All aquatic phototrophs are depleted in
δ 13 C relative to dissolved inorganic carbon (DIC), because Rubisco discriminates
against 13 C (Hu et al. 2012).
The spatial and temporal variability of δ 13 C values in aquatic organisms
depends on several factors such as isotopic shifts in available inorganic carbon,
resulting from light-induced HCO 3
− utilization, variation in solar intensity, differences in water temperature, internal recycling of respiratory CO 2 , photoinduced
generation of DIC from DOM and POM, and dissolution of sedimentary carbonate
(Yoshioka 1997; Raven et al. 2002; Jones 1992; Ma and Green 2004; Xie et al.
2004; White et al. 2010; Liu et al. 2010; Dreybrodt 1988; Hemminga and Mateo
1996; Campbell and Fourqurean 2009). It is shown that [CO 2 ] aq concentration is
inversely correlated with the δ 13 C of organic matter produced by phytoplankton
(Rau et al. 1992; Freeman and Hayes 1992). The carbon isotope fractionation of
phytoplankton could be a useful indicator for the assessment of its growth rate
and of CO 2 availability (Fogel et al. 1992; Takahashi et al. 1991). Phytoplankton
can actively transport CO 2 by a carbon-concentrating mechanism (CCM) that can
affect its δ 13 C value (Yoshioka 1997; Sharkey and Berry 1985; Bums and Beardall
1987; Thielmann et al. 1990). Correspondingly, ß-carboxylation catalysed by
phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase can
affect the δ 13 C of phytoplankton (Descolas-Gros and Fontugne 1985; Falkowski
1991).
To understand the mechanism behind the uptake of CO 2 or HCO 3
− , a fractionation
equation was developed for plant photosynthesis (O’Leary 1981; Farquhar et al. 1989;
Raven et al. 1993) and phytoplankton photosynthesis (Fogel et al. 1992; Rau et al.
1992; Francois et al. 1993; Jasper and Hayes 1994; Laws et al. 1995; Yoshioka 1997;
Berry 1988).
5.2.1 Basic Equation for Expressing Photosynthetic Carbon Isotope
Fractionation
The photosynthetic carbon isotope fractionation is initially derived based on the
land C 3 plants (O’Leary 1981; Farquhar et al. 1989; Yoshioka 1997). The photosynthetic process for uptake of carbon can be depicted as follows (Yoshioka 1997)::
where k i is the rate constant for process i. Processes 1 and 3 are the diffusive influx
and efflux of CO 2 , respectively, whilst process 2 is the carboxylation step by
(5.9)
[CO 2 ] out
k 1
←→
k 3
[CO 2 ] in −→ k 2 organic carbon
K. M. G. Mostofa et al.
δ 13 C value in the phytoplankton bloom season suggests that phytoplankton photosynthesis may be limited by CO 2 depletion (Takahashi et al. 1990). It has been
observed that aqueous CO 2 , [CO 2 ] aq , determined in freshwater and marine waters
is relatively low (0.13–35 M) in freshwater and relatively higher (5–120 M)
in seawater (Fogel et al. 1992; Francois et al. 1993; Yoshioka 1997; Takahashi
et al. 1990; Herczeg and Fairbanks 1987). All aquatic phototrophs are depleted in
δ 13 C relative to dissolved inorganic carbon (DIC), because Rubisco discriminates
against 13 C (Hu et al. 2012).
The spatial and temporal variability of δ 13 C values in aquatic organisms
depends on several factors such as isotopic shifts in available inorganic carbon,
resulting from light-induced HCO 3
− utilization, variation in solar intensity, differences in water temperature, internal recycling of respiratory CO 2 , photoinduced
generation of DIC from DOM and POM, and dissolution of sedimentary carbonate
(Yoshioka 1997; Raven et al. 2002; Jones 1992; Ma and Green 2004; Xie et al.
2004; White et al. 2010; Liu et al. 2010; Dreybrodt 1988; Hemminga and Mateo
1996; Campbell and Fourqurean 2009). It is shown that [CO 2 ] aq concentration is
inversely correlated with the δ 13 C of organic matter produced by phytoplankton
(Rau et al. 1992; Freeman and Hayes 1992). The carbon isotope fractionation of
phytoplankton could be a useful indicator for the assessment of its growth rate
and of CO 2 availability (Fogel et al. 1992; Takahashi et al. 1991). Phytoplankton
can actively transport CO 2 by a carbon-concentrating mechanism (CCM) that can
affect its δ 13 C value (Yoshioka 1997; Sharkey and Berry 1985; Bums and Beardall
1987; Thielmann et al. 1990). Correspondingly, ß-carboxylation catalysed by
phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase can
affect the δ 13 C of phytoplankton (Descolas-Gros and Fontugne 1985; Falkowski
1991).
To understand the mechanism behind the uptake of CO 2 or HCO 3
− , a fractionation
equation was developed for plant photosynthesis (O’Leary 1981; Farquhar et al. 1989;
Raven et al. 1993) and phytoplankton photosynthesis (Fogel et al. 1992; Rau et al.
1992; Francois et al. 1993; Jasper and Hayes 1994; Laws et al. 1995; Yoshioka 1997;
Berry 1988).
5.2.1 Basic Equation for Expressing Photosynthetic Carbon Isotope
Fractionation
The photosynthetic carbon isotope fractionation is initially derived based on the
land C 3 plants (O’Leary 1981; Farquhar et al. 1989; Yoshioka 1997). The photosynthetic process for uptake of carbon can be depicted as follows (Yoshioka 1997)::
where k i is the rate constant for process i. Processes 1 and 3 are the diffusive influx
and efflux of CO 2 , respectively, whilst process 2 is the carboxylation step by
(5.9)
[CO 2 ] out
k 1
←→
k 3
[CO 2 ] in −→ k 2 organic carbon