2.5 Carbon analysis
Samples of biomass were ground in liquid nitrogen in a mortar and pestle to a particle size of 500 μm. The oil-bath K2Cr2O7 titration method was used for estimating organic C in the plant tissues (Dong 1997), and organic C content of the soil samples was estimated using the K2Cr2O7 volumetric dilution heating method (Nelson and Sommers 1982).
Calculating total carbon storage and statistical analysis
Carbon content of trees, herbs, and litter was determined by multiplying the respective biomass by its C content. The total stock of soil organic C (SOC) to a depth of 100 cm was calculated based on its organic C content, sample depth, and bulk density (Guo and Gifford 2002) as follows: SOC = BD × Cc / 100 × D, where BD is soil bulk density (g/cm³), Cc is soil C concentration (%), and D is soil sampling depth (cm). Ecosystem carbon storage was calculated as the total of each component (trees, herbs, litter, and soil):
\begin{equation} C_{T}=C_{t}+C_{h}+C_{l}+C_{S}\nonumber \\ \end{equation}
where CT is total ecosystem C, Ct is the total C stored in trees (t/ha); Ch, that in herbs (t/ha); Cl, that in litter; and Cs, that in soil (t/ha in each case).