2.3 Soil collection and indoor analysis
In this study, we first selected three sample sites with approximately the same plant community composition within each of the five sample plots of MS, 5yrs, 11yrs, 22yrs, and 46yrs, and sampled the same soil stratum in three replicates at each sample site in 20 cm strata. The soil collected in each stratum was mixed thoroughly and divided into two groups of samples within the three sample points of the five forest age sample plots. One group measured the SIC content and the other group tested soil moisture. To determine the soil volume, we collected complete soil samples using a stainless steel soil sampler with a volume of 100 cm3. After collecting the soil, we air dried it and passed it through a 2 mm sieve to remove any rocks or root systems larger than 2 mm. To analyze these samples, we ground them with a ball mill and passed them through a 100 mesh soil sieve. Soil inorganic carbon was determined by the air volumetric method, soil pH (water to soil ratio of 2.5:1) was determined by the electrode method, and soil bulk weight was the dry mass per unit volume of soil at 105°C. Soil moisture was determined by weighing the fresh weight of the soil, then drying it at 105°C and weighing the dry weight.