[gtsop]

I think more information is needed as input here. In pwrticular, what is the ratio of consumed/stored co2 in the photosynthesis process. My super basic understanding is that co2 is being used as fuel to convert energy into tree-food. By that logic i would expect at least a portion of the co2 to be actually transformed to other elements rather than stored as-is into the tree.

[downWidOutaFite]

Your intuition is correct. The basic photosynthesis chemical formula is

  6CO2 + 6H2O + (light) ---> C6H12O6 + 6O2

The carbon goes from CO2 to C6H12O6, which are carbohydrates. The carbs are used by the plants for both energy and plant matter. The carbs that are used for energy are released back into the atmosphere as CO2 via cellular respiration. For carbon sequestration what matters is that the carbon in the plant matter stays fixed and doesn't get converted back into CO2 and released.