Effects of plant carbon inputs and soil microbe on soil organic carbon accumulation in different tropical vegetation restoration strategies

Abstract

Vegetation restoration is an important measure for improving soil carbon sequestration in degraded agricultural ecosystems. However, the soil organic carbon (SOC) dynamics under different vegetation restoration strategies in tropical regions are understood well. This study investigated SOC, biotic, and abiotic factors across the soil profile (0–20 cm, 20–40 cm, and 40–60 cm) for four vegetation restoration strategies, including Hopea hainanensis × Homalium ceylanicum (HH), Syzygium cumini × Dalbergia odorifera (SD), Aquilaria sinensis × Hopea hainanensis (AH), and Syzygium cumini × Hopea hainanensis (SH), with barren land (CK) and secondary forest (SF) as the control and reference groups, respectively. Our findings demonstrated that vegetation restoration effectively increased the SOC content. In comparison to CK, the SOC content was relatively high in SD (12.82 ± 0.59 g/kg–18.50 ± 0.97 g/kg) and SH (14.67 ± 0.22 g/kg–20.15 ± 0.91 g/kg) following vegetation restoration in the 0–20 and 20–40 cm soil layers (P < 0.05). This depends on the difference in biomass produced by different tree species' combinations, and high plant carbon inputs in SD (388.45 ± 44.61 g/kg) and SH (424.88 ± 18.92 g/kg) treatments will accelerate the return of carbon to soil. The results of the random forest and PLS-PM models identified that microbial biomass carbon (MBC) and microbial necromass carbon (MNC) were the two most important SOC predictors, which promote SOC accumulation in conjunction with plant-derived carbon. Further, it was also found that soil nutrient availability enhanced SOC accumulation by promoting the production of MNC. This process was negatively associated with carbon-acquiring enzyme activities. This study could provide a reference for the selection of SOC sequestration vegetation restoration strategies in tropical forests of southern China.