Btw, how is this known as a fact:
"This is because plants have a preference for the lighter isotopes (12C vs. 13C); thus they have lower 13C/12C ratios."
http://www.realclimate.org/index.php?p=87

How does a plant select to use the lighter isotopes?
And if this is true, do or can we use plants to sort of elements with lighter isotopes.
Apparently the human body can't do this- heavy water is posionous to humans because the human body absorbs it and it becomes part of human biology- the result being that haevier element slows down chemical reactions significantly- at least according what I was reading lately. It also said the heavier hydrogen element had this affect because it's mass was significantly increased and that is a not as significant of other types of isotopes because with other element it less of difference in the entire mass of the element.

Therefore I could see that plants could have a slight evolutional advantage if they could sort isotopes, but question do they do this and how do they do this? And if this is a plant gene, could to tranfers to animals or different organism which could sort different element other than carbon?