The only way to measure the release of carbon dioxide what is sequestered by plants is measure the biomass of the plants. This can be done through estimating allometric relationships between something that is easily measured non-destructively (basal diameter of stem, etc.) and the biomass of the plant.
Cecilia Geronimo I am not an expert on this matter, but from what I know I agree with Muhammad Amjad . Logically, leave size alone cannot be the determinant. There may be very small plant species that have large leaves, but overall small biomass, meaning those plants could not store large amounts of carbon. C sequestration can also be affected by characteristics of the species above and below ground (i.e., root structure), and by the volume of leaf litter. As an example, see this manuscript: Article Carbon sequestration potential of five tree species in a 25-...
For examples of estimation of above ground biomass see: https://www.scirp.org/journal/paperinformation.aspx?paperid=109346