Soil organic carbon (SOC) is the largest carbon pool in terrestrial ecosystems, playing a vital role in climate regulation and ecosystem sustainability. SOC accumulation involves two fundamental processes: SOC formation and stability.

A recent study published in Environmental Science & Technology by a research team led by Professor WANG Kelin from the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences, highlighted the trade-off between microbial-mediated SOC formation and stabilization.

Microbial carbon use efficiency (CUE) refers to the proportion of assimilated carbon retained in microbial biomass. High CUE promotes SOC formation by driving microbial growth and the production of necromass through microbial death. Meanwhile, the stabilization of microbial necromass by soil aggregates and minerals enhances SOC stability.

However, the physical and chemical protection provided by soil aggregates and minerals, while stabilizing organic matter, can limit the availability of substrates for microbes, reducing their CUE and, consequently, SOC formation.

In their new study, the ISA team measured microbial CUE in well-aggregated bulk soils and crushed aggregates, and further analyzed microbial necromass in bulk soils and the mineral-associated organic matter fraction across karst and non-karst soils under varying climatic conditions in southwest China.

“We found that soil aggregation and mineral protection decreased microbial CUE and necromass production, they simultaneously enhanced microbial necromass stability,” said Prof. WANG.

The trade-off between SOC formation and stability is regulated by bedrock lithology.

“Karst soils, with higher mineral content and greater mineral preservation capacity, exhibited a stronger trade-off than non-karst soils,” said Prof. ZHANG Wei, a co-corresponding author of the study and researcher at ISA.

Relying solely on microbial CUE to predict soil carbon sequestration potential can be misleading, according to the study. It highlighted the dual role of soil minerals in influencing both microbial necromass formation and stabilization, which should be carefully considered to optimize carbon sequestration strategies in karst ecosystems.

Conceptual diagram illustrating how soil aggregates and minerals reduce microbial CUE while enhancing microbial necromass stability. (Image by HU Peilei)