How can cane sugar sucrose be different from beet sugar in regard to carbon-13 content? According to an article in SCIENZA IN CUCINA, by Dario Bressanini, le Scienze Blog content of $^{13}C$ differs in sucrose in beet sugar compared to cane sugar. What is this due to? Are there any similar examples? Is the difference in synthesis enough to explain the difference? One could guess that the weight of the carbon molecule is more critical in one of the synthesis chains.

The differential uptake of different isotopes of carbon is covered well at:

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Plants have a lower proportion of C-13 than atmospheric CO2.

The two mechanisms that cause this are the reduced diffusion speed of the heavier C-13, and an energetic difference in the chemical reactions that favours C-12.

In sugar cane (C4 photosynthesis) the carbon dioxide is captured in an additional step compared with sugar beet (C3 plant).

This capture step in C4 plants (using phosphoenolpyruvate carboxylase) is less exclusive toward C-13, so the carbon in these plants has detectably more C-13 than C3 plants.

This subsequently affects the isotopic proportion of all the carbon in the plant