Abstract:

Objective: This study aims to investigate the variation patterns of soil organic carbon (SOC) and its physical, chemical, and microbial carbon fractions during moso bamboo (Phyllostachys edulis) expansion, and to clarify the effects of each carbon fraction on SOC accumulation. Method: The proportion of basal area at breast height (BA%) of P. edulis was used to quantitatively characterize expansion intensity. A typical successional sequence formed by bamboo expansion into Chinese fir forests (Cunninghamia lanceolata), including pure C. lanceolata forest, mixed P. edulis-C. lanceolata forests at early, middle, and late expansion stages, and pure P. edulis forest was taken as the research object. Soil samples were collected from the 0–50 cm soil profile to study the characteristics of SOC and its physical, chemical, and microbial carbon fractions in different forest stands. Boosted regression tree model and multiple stepwise regression analysis were employed to quantify the relative effects of each carbon fraction on SOC accumulation. Result: Mixed P. edulis-C. lanceolata forest at the middle expansion stage (MCF-M, 35%<BA%≤65%) exhibited the strongest soil carbon sequestration capacity. In the top soil (0–20 cm), SOC content (17.66–38.65 g·kg^?1) and physical and chemical carbon fractions were significantly higher in MCF-M than those of the other four forest stands (P<0.05). In the 20–50 cm soil layer, there were no differences in physical and chemical carbon fractions among forest stands except for mineral-associated organic carbon (P>0.05). Unlike the surface enrichment of physical and chemical carbon fractions, the microbial necromass carbon and fungal and bacterial components in MCF-M were significantly higher than those in other forest types in the 0–50 cm soil profile (P<0.05). The boosted regression tree model revealed that the three types of carbon fractions jointly explained 83.25% of SOC variation in the 0–20 cm layer, with the relative influence ranked as microbial carbon fractions (55.51%) > physical carbon fractions (35.42%) > chemical carbon fractions (9.07%). Multiple stepwise regression analysis showed that both microbial necromass carbon and mineral-associated organic carbon were significantly positively associated with SOC accumulation (P<0.001). Conclusion: Collectively, MCF-M exhibits superior soil carbon sequestration capacity during P. edulis expansion. The synergistic variation of microbial necromass accumulation and mineral protection is closely associated with SOC accumulation.

Key words: moso bamboo forests, mixed forests, organic carbon sequestration, microbial necromass carbon, mineral-associated organic carbon