Using Models of Carbon Isotope Fractionation during Photosynthesis to Understand the Natural Fractionation Ratio

Abstract

The fractionation correction b is used to correct for the fractionation of 14 C by using information from 13 C in samples. This value is assumed to have a value of 2, where the 14 C/ 12 C ratio is double that of the 13 C/ 12 C ratio. While natural and laboratory fractionation are usually not considered separately, this article explores the differential fractionation of 14 C and 13 C during the process of photosynthesis. Values of δ 13 C p can be used to calculate Δ 13 C p values, which in turn can be used to calculate Δ 14 C p , the discrimination against 14 CO 2 during photosynthesis. Models can then be built of Δ 14 C p /Δ 13 C p , an approximation for the natural fractionation ratio. This approximation suggests that for C 3 plants the ratio is ~1.90 and for C 4 plants the ratio is more variable. While error introduced by the natural fractionation is small, it is also possibly systematic, as b = 2.0 does not seem physiologically possible following these models of carbon fractionation during photosynthesis. The central aim of this study is to illustrate that b derives not from a natural constant, but rather from a variable natural process.

Advances in measurements and models of photosynthetic carbon isotope discrimination in C3 plants

“…If the objective is to derive g m or other parameters from measurements and models of discrimination, the detailed equation is required. Alternatively, for crude applications, such as using Δ 13 C to correct 14 C data (Drake ), it would seem pointless going beyond the simplest model. As illustrated by Gentsch et al .…”

“…If the objective is to derive gm or other parameters from measurements and models of discrimination, the detailed equation is required. Alternatively, for crude applications, such as using Δ 13 C to correct 14 C data (Drake 2014), it would seem pointless going beyond the simplest model. As illustrated by Gentsch et al (2014), the diurnal variation in Δobs was mostly explained by the contributions of stomatal and mesophyll conductances and photorespiration, which could be approximated by Δ Δ sim b f − − .…”

Coupling use of stable isotopes and functional genes as indicators for the impacts of artificial restoration on the carbon storage of a coastal wetland invaded by Spartina alterniflora, southeastern China

“…SOM than S.alterniflora. Previous studies have reported that the production of C3 plants tend to exhibit greater isotopic fractionation between 12 C and 13 C (Reibach and Benedict, 1977;Roeske and O'Leary, 1984;Drake, 2014). Hence the photosynthetic products derived from C3 plants are usually characterized by lower d 13 C than that derived from C4 plants.…”

Supplementary material to "A new terrestrial biosphere model with coupled carbon, nitrogen, and phosphorus cycles (QUINCY v1.0; revision 1772)"

“…Isotopic discrimination of 13 C and 14 C by photosynthesis is modelled according to the general equation derived by Farquhar et al (1982); Drake (2014), so that…”