Most things on this planet are heterotrophic....and i understand what you are saying ,it seems plausable. Given that mosses/algae grow were the conditions are idea ie damp/shaded areas.You would take it that it would follow suit...ie a higher Carbon content.
Saying that tho' We should have rainforests at the side of the motorways.
What we do have is the biologist Dr Pamela E Simpson...we shall ask her...when we recover the missing Frenchman