The study looked at soil carbon in Korean pine and broadleaf forests at different stages of growth. They found that as the forests aged, the levels of certain types of carbon in the soil increased until reaching a balance at maturity. The amount of carbon also decreased with soil depth. The top layer had more dissolved organic carbon and microbial biomass carbon, while the deeper layers had more easily oxidized carbon. The proportion of easily oxidized carbon decreased with depth, while dissolved organic carbon increased. The study also found significant correlations between soil carbon levels and soil nutrients.