Accumulation of chemically degraded organic carbon in the soil profile of Chinese fir plantations

Abstract

Short-rotation forestry relies on frequent harvests of fast-growing trees, which could deplete soil fertility and soil organic carbon (SOC) reserves. Our objective was to measure the accumulation of SOC fractions, namely the dissolved organic carbon, microbial biomass carbon, particulate organic carbon, permanganate-oxidizable carbon, and non-oxidizable organic carbon, in the soil profile of a Chinese fir plantation. Chronosequences of Chinese fir aged 7, 12, and 33 yr were sampled at depths of 0–20 cm, 20–40 cm, and 40–60 cm. The SOC stock (0–60 cm) was unchanged in the first 12 yr, but after 33 yr, there was a 41%–56% increase in the SOC stock, which reached 81.2 Mg ha−1 (P < 0.05). Permanganate-oxidizable carbon increased with time in the 0–20 cm layer but not in deeper soil depths, whereas non-oxidizable organic carbon accumulated preferentially in the 40–60 cm layer of the soil profile. Inputs of chemically complex plant litter in the soil profile may be important to maintain the oxidizable and non-oxidizable organic carbon in Chinese fir plantations.