20 May 2024

How organic carbon accumulates in acidified forest soils


A study by the Chinese Academy of Sciences reveals how forest soil acidification promotes both mineral protection and plant-derived carbon accumulation

by Matteo Cavallito


Acidification is known to pose a threat to soils. Its impact on soil’s ability to sequester carbon, however, is not fully understood. Little is known, in particular, on soil carbon accumulation in fully developed tropical and subtropical forests, which have long been highly acidified. These include China‘s southern forests, that contribute to the storage of more than half of the organic carbon stored in that country’s forest ecosystem. Nthese ecosystems have recently been the subject of study.

The study

Shedding light on the phenomenon of carbon sequestration, in fact, have been researchers from the South China Botanical Garden of the Chinese Academy of Sciences. Through an experiment conducted in Dinghushan Nature Reserve, Guangdong Province, the authors were able to describe the mechanism of carbon accumulation and stabilization in monsoon evergreen broadleaf forests.

The investigation involved two components of organic matter: particulate organic carbon (POC) and mineral-associated carbon (MAOC). The researchers then set out to assess what mechanism and factors affected the collection of organic fractions.

“We conducted a 11-year field acid addition experiment to study how acid deposition affected the accumulation of soil organic carbon and its fractions,” says the study published in the journal Plant and Soil. “Lignin phenols and amino sugars were used as two tracers for plant- and microbe-derived carbon.”

Acidification promotes carbon accumulation

“We found that both POC (0–20 cm) and MAOC (10–20 cm) were significantly increased by acid addition,” the authors explain. These, in particular, “significantly reduced the contributions of fungal-, bacterial- or total microbial residue carbon to SOC but significantly increased the plant-derived soil carbon in both soil depths.” In addition, the addition of acid particularly increased the lignin phenol from plants. And not without consequences.

“The increase of lignin phenol and suppressed soil organic matter decomposition from soil microbes suggested that soil POC increased with acid addition,” the researchers explain. “Soil acidification strongly enhanced MAOC accumulation through increased lignin and mineral protection by iron-aluminum oxides and cations.”

New information on forest dynamics

These results, the scientists conclude in a statement, suggest that mineral protection and continuous supply of plant-derived carbon enhanced the accumulation and stabilization of organic element with soil acidification. The results “provide mechanistic support for the function of continuous carbon sequestration in deeply acidified forest soils.” Thus adding new insights into these kinds of dynamics.

The topic has long been of interest to researchers in the country. Last year, a study by the Chinese Academy of Sciences itself highlighted in particular the crucial interactions between different species of fungi and plant biomass in forest ecosystems. The investigation revealed that in forests dominated by shrubs, the stock of carbon in the subsoil exceeds the amount recorded in forests where ectomycorrhizal fungi are prevalent by 25 percent. The ways in which these microorganisms influence the distribution of carbon among trees, however, are not yet known.