2-2-3- Step 3- Estimating carbon storage in an individual tree unit
Once the biomass of a single tree was calculated using the allometric equations, carbon storage in the above-ground biomass (trunk and crown) and the below-ground (root) was calculated through equation 1 and 2(Aboal et al., 2005, Kirby and Potvin, 2007, Pearson, 2007, Peichl and Arain, 2006).
\begin{equation} C_{\text{AGB}}=AGB*C\%\ \ \ \ \ \ \ \ Eq.1\nonumber \\ \end{equation}\begin{equation} C_{\text{BGB}}=BGB*C\%\ \ \ \ \ \ \ \ Eq.2\nonumber \\ \end{equation}
Where CAGB indicates carbon in the above-ground biomass (kg ), AGB is the above-ground biomass of tree (kg ), CBGB is the amount of carbon in below-ground biomass (kg ), BGB stands for the below-ground biomass(kg ), and C% is carbon percentage (the amount of carbon storage in biomass or carbon conversion efficient). The results of previous studies showed that the carbon conversion ratio in the biomass of different tree species varies between 44.4% to 55.7%, and usually in most studies, it is equivalent to an average of 50% of the dry mass (Elias and Potvin, 2003; Singh et al., 2011; Zhang et al., 2009; Zhu et al., 2010). While, in this research, to estimate the amount of carbon in the biomass, instead of using the coefficient (50%), we used the photosynthesis chemical equation. The well-known chemical photosynthesis equation is explained as follows (Blankenship, 2014):
\begin{equation} {6CO}_{2}\ \left(264\ g\right)+\ 6H_{2}\text{O\ }\left(108\ g\right)+light\rightarrow C_{6}H_{12}O_{6}\ \left(180\ g\right)+\ {6O}_{2}\ \left(193\ g\right)\ \rightarrow\ Amylase\ (162\ g)\nonumber \\ \end{equation}
The molecular weight of carbon dioxide is 44.9595 g / mol ; therefore, plants absorb six molecules of CO2, i.e., 264 gram of carbon dioxide, 162 gram of amylase, or dry matter (Blankenship, 2014). Therefore, it can be said that each kilogram of dry matter (produced by trees) absorbs 1.629 kilograms of carbon dioxide. Based on this equation, considering that the atomic weight of carbon is 12.01 grams, therefore, for absorbing 6 molecules of carbon dioxide, around 72 grams of carbon is fixed in the biomass. In general, for every kilogram of dry matter produced in a tree, approximately 453 grams of carbon is stored in the biomass of a tree.