Soil organic carbon (SOC) sequestration in tropical and subtropical forests plays a key role in mitigating global climate change. The impact of human activities on soil carbon sink potential in the tropics has aroused wide concerns at global scale. However, it is still unclear how the legacy effect of land-use history affects SOC stability. 

To address the question, Prof. LU Xiankai and Dr. SU Fanglong from the South China Botanical Garden of the Chinese Academy of Sciences (CAS) studied the SOC sequestration mechanisms through selecting two typical tropical forest ecosystems at Dinghushan National Nature Reserve, including an evergreen broadleaf forest (primary forest) and a Masson pine coniferous forest (planted forest after clear-cutting of primary forest).  

The resear found that the primary forest had a larger SOC pool than the planted forest. SOC as the macroaggregate fraction (diameter > 250 μm) or heavy fraction (density > 1.8 g cm^-3) dominated soil carbon pool in the two forests, and their proportions to total SOC were similar between the two forests. However, soil carbon conservation in microaggregates (< 250 μm in diameter) and mineral-bound carbon showed divergent patterns between the two forests.  

Although a greater proportion of SOC was stored as microaggregates in the planted forest at the same soil layer, the concentration and content of mineral-bound organic carbon were significantly higher in the primary forest, which ultimately led to the lower stability of SOC in the planted forest than that in the primary forest. 

The results suggest that the transition from the primary forest to the planted forest can alter the physical and chemical protection of SOC, which will decline soil carbon sequestration capacity.  

Furthermore, changes in forest tree species composition could have long-lasting effects on soil structure and carbon storage. This study can provide crucial evidence for policy decisions on forest carbon sink management under global changes. 

This study, published in Journal of Environmental Management, was supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of CAS, the Natural Science Foundation of Guangdong Province and the China Postdoctoral Science Foundation.