Carbonate rocks such as limestone and dolostone help soils hold on to carbon as they weather. A new study in National Science Review finds that carbonate rock weathering promotes the buildup of microbial necromass, the remains of dead microbes, and helps protect it from decomposition. The study, led by researchers at the Institute of Subtropical Agriculture, Chinese Academy of Sciences, combined global soil datasets, field surveys in southwestern China and controlled laboratory experiments.
Soil organic carbon is critical for climate regulation, nutrient cycling, water retention and biodiversity maintenance. Microbes make up a large portion of soil organic carbon: they feed on plant-derived carbon, grow and multiply, then leave behind their necromass when they die. How much of microbial necromass accumulates depends on how efficiently microbes use carbon to grow and how well their necromass is protected from decomposition.
Both processes are strongly shaped by soil conditions, which are in turn largely influenced by underlying bedrock. Carbonate rocks underlie about 15% of Earth's ice-free land and dissolve at least ten times as fast as many silicate rocks. Their weathering releases calcium and nutrients and alters soil acidity, affecting microbial activity and the binding of organic matter to minerals. Yet research on carbonate rock weathering and carbon cycling has largely focused on carbon dioxide uptake during rock dissolution. Its effects on soil organic carbon are less well understood.
The team analyzed 466 observations of forest topsoils worldwide, using amino sugars as biomarkers of microbial necromass. Soils in karst landscapes, shaped by the dissolution of carbonate rocks, had 43.4% higher amino sugar concentrations and 57.6% higher organic carbon concentrations than non-karst soils. These differences remained significant after accounting for climate and vegetation covariates.
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