599
Photosynthesis in Nature: A New Look
2005). The proportion of each species depends on pH: at high pH the reaction shifts
to the right hand side of (Eq. 5.8) and HCO 3
− dominates at pH between 7 and 9,
approximately 95 % of the carbon in water. At pH > 10.5, CO 3
2− predominates
(Dreybrodt 1988). The equilibrium constants for this system are altered by the salinity
of the medium: the values for seawater are an order of magnitude higher than those of
freshwater toward the right-hand-side of the reaction (Raven et al. 2002; Millero and
Roy 1997).
It is well known that the stable carbon isotope composition (δ 13 C value) of
organic matter, produced either by phytoplankton or terrestrial plants during
photosynthesis, is significantly varied depending on the taxon-specific photosynthetic pathways (such as C 3 , C 4 , and crassulacean acid metabolism, CAM).
It also varies depending on: variety of phytoplankton; diffusion of CO 2 ; incorporation of CO 2 by phosphoenolpyruvate carboxylase or Ribulose Bisphosphate
Carboxylase-Oxygenase (Rubisco), and respiration; sources and interconversion of
CO 2 and HCO 3
− (depending on a variety of environmental conditions including
light intensity, temperature, DOM and POM contents, water depth, atmospheric
CO 2 concentration and so on) (O’Leary 1981; Cooper and McRoy 1988; Farquhar
et al. 1989; Raven and Farquhar 1990; Yoshioka 1997; Raven et al. 2002; Hu
et al. 2012). Note that the δ 13 C values of [CO 2 ] aq and DIC are −16.5 to −14.5 ‰
and −7.4 to −4.5 ‰, respectively (Yoshioka 1997). The values of δ 13 C of organic
matter in marine macroalgae and seagrass collected from the natural environment
can vary from –2.7 ‰ to –35.3 ‰ (Raven et al. 2002; Hu et al. 2012; Beardall
2003; Hemminga and Mateo 1996; Raven 1997; Dunton 2001). Plants with C 4
characteristics show δ 13 C values of −6 to −19 ‰ whilst plants with C 3 characteristics exhibit δ 13 C values of −24 to −34 ‰ (Smith and Epstein 1971).
Such variation in the δ 13 C value can be caused by (Farquhar et al. 1989; Raven
and Farquhar 1990): (i) the isotope fractionation factor (α), which is the ratio of
the reaction rates of 12 CO 2 and 13 CO 2 with Rubisco (α = 1.029 for gaseous CO 2
and α = 1.030 for dissolved CO 2 ); (ii) the relative contribution of phosphoenolpyruvate carboxylase (PEPC) activity to the photosynthetic carbon assimilation; and (iii) the supply of CO 2 to Rubisco is restricted by the boundary layer,
stomata, and intercellular gas spaces that can differ for CO 2 diffusion in the gas
phase (α = 1.0044), and in the aqueous phase (α = 1.0007).
The δ 13 C values of POM are varied spatially and seasonally. They increase
with increasing pH of lake water, which may reflect a shift by phytoplankton from using CO 2 to using HCO 3
− for photosynthesis (Zohary et al. 1994;
Doi et al. 2006). The pH is increased with increasing water temperature during the time span of the summer stratification period, which may be connected with photoinduced degradation of DOM and POM (see also chapter
“Photoinduced and Microbial Degradation of Dissolved Organic Matter in Natural
Waters”) (Kopác ˇek et al. 2003; Mostofa et al. 2005). Photoinduced generation of
H 2 O 2
2O 2
•− + 2H + → H 2 O 2 + O 2
(Mostofa and Sakugawa 2009; Fujiwara
et al. 1993) might be one of the key factors for enhancing alkalinity or pH in
waters. Therefore, uptake of HCO 3
− for phytoplankton photosynthesis at high pH
might be the effect of its dominant presence in waters. A significant increase in the
Photosynthesis in Nature: A New Look
2005). The proportion of each species depends on pH: at high pH the reaction shifts
to the right hand side of (Eq. 5.8) and HCO 3
− dominates at pH between 7 and 9,
approximately 95 % of the carbon in water. At pH > 10.5, CO 3
2− predominates
(Dreybrodt 1988). The equilibrium constants for this system are altered by the salinity
of the medium: the values for seawater are an order of magnitude higher than those of
freshwater toward the right-hand-side of the reaction (Raven et al. 2002; Millero and
Roy 1997).
It is well known that the stable carbon isotope composition (δ 13 C value) of
organic matter, produced either by phytoplankton or terrestrial plants during
photosynthesis, is significantly varied depending on the taxon-specific photosynthetic pathways (such as C 3 , C 4 , and crassulacean acid metabolism, CAM).
It also varies depending on: variety of phytoplankton; diffusion of CO 2 ; incorporation of CO 2 by phosphoenolpyruvate carboxylase or Ribulose Bisphosphate
Carboxylase-Oxygenase (Rubisco), and respiration; sources and interconversion of
CO 2 and HCO 3
− (depending on a variety of environmental conditions including
light intensity, temperature, DOM and POM contents, water depth, atmospheric
CO 2 concentration and so on) (O’Leary 1981; Cooper and McRoy 1988; Farquhar
et al. 1989; Raven and Farquhar 1990; Yoshioka 1997; Raven et al. 2002; Hu
et al. 2012). Note that the δ 13 C values of [CO 2 ] aq and DIC are −16.5 to −14.5 ‰
and −7.4 to −4.5 ‰, respectively (Yoshioka 1997). The values of δ 13 C of organic
matter in marine macroalgae and seagrass collected from the natural environment
can vary from –2.7 ‰ to –35.3 ‰ (Raven et al. 2002; Hu et al. 2012; Beardall
2003; Hemminga and Mateo 1996; Raven 1997; Dunton 2001). Plants with C 4
characteristics show δ 13 C values of −6 to −19 ‰ whilst plants with C 3 characteristics exhibit δ 13 C values of −24 to −34 ‰ (Smith and Epstein 1971).
Such variation in the δ 13 C value can be caused by (Farquhar et al. 1989; Raven
and Farquhar 1990): (i) the isotope fractionation factor (α), which is the ratio of
the reaction rates of 12 CO 2 and 13 CO 2 with Rubisco (α = 1.029 for gaseous CO 2
and α = 1.030 for dissolved CO 2 ); (ii) the relative contribution of phosphoenolpyruvate carboxylase (PEPC) activity to the photosynthetic carbon assimilation; and (iii) the supply of CO 2 to Rubisco is restricted by the boundary layer,
stomata, and intercellular gas spaces that can differ for CO 2 diffusion in the gas
phase (α = 1.0044), and in the aqueous phase (α = 1.0007).
The δ 13 C values of POM are varied spatially and seasonally. They increase
with increasing pH of lake water, which may reflect a shift by phytoplankton from using CO 2 to using HCO 3
− for photosynthesis (Zohary et al. 1994;
Doi et al. 2006). The pH is increased with increasing water temperature during the time span of the summer stratification period, which may be connected with photoinduced degradation of DOM and POM (see also chapter
“Photoinduced and Microbial Degradation of Dissolved Organic Matter in Natural
Waters”) (Kopác ˇek et al. 2003; Mostofa et al. 2005). Photoinduced generation of
H 2 O 2
2O 2
•− + 2H + → H 2 O 2 + O 2
(Mostofa and Sakugawa 2009; Fujiwara
et al. 1993) might be one of the key factors for enhancing alkalinity or pH in
waters. Therefore, uptake of HCO 3
− for phytoplankton photosynthesis at high pH
might be the effect of its dominant presence in waters. A significant increase in the