Soils store more carbon than the atmosphere and vegetation combined, making them a crucial part of climate change mitigation. Biochar, a carbon-rich material produced by heating biomass in limited oxygen, has attracted growing attention because it can remain in soil for long periods and may help stabilize soil carbon. But what happens when biochar is added to living, root-filled soil is more complex than simply “locking carbon away.”
A study published in Biochar reveals that biochar can reshape the microscopic life around plant roots, altering how soil organic carbon is broken down, transformed, and accumulated. The research focused on the rhizosphere, the narrow zone of soil influenced by plant roots, where root exudates, soil minerals, and microbial communities interact intensely.
Using maize grown in paddy soil, the researchers tested how a 2% bamboo biochar amendment affected soil carbon dynamics over 99 days of plant growth. They used a natural abundance carbon isotope approach to separate root-derived carbon dioxide from soil-derived carbon dioxide, allowing them to track the rhizosphere priming effect, a process in which living roots stimulate or suppress the decomposition of native soil organic matter.
The results showed that biochar did not simply reduce carbon loss. Instead, it altered the rhizosphere priming effect across maize growth stages, ranging from a 116.96% decrease to a 171.59% increase. Across the full growth period, biochar increased total soil organic carbon, reduced dissolved organic carbon, raised soil pH, and shifted microbial communities toward organisms adapted to lower nutrient availability.
“Our findings show that biochar in planted soil is not just a passive carbon storage material,” said corresponding author Jingping Yang. “It actively changes the biological engine of the rhizosphere. By reshaping microbial functions, especially bacterial carbon cycling, biochar can promote both soil carbon mineralization and carbon accumulation within a short period.”
A key finding was that fungi and bacteria responded differently to biochar. Biochar decreased fungal abundance but increased bacterial abundance. It also changed microbial network patterns and enriched bacterial functional groups involved in carbon cycling. Functional genes associated with both carbon degradation and carbon fixation increased under biochar application, suggesting that bacteria played a central role in driving the observed carbon changes.
This microbial “double action” helps explain why biochar can sometimes produce seemingly contradictory outcomes. It may stimulate the breakdown of existing soil organic carbon while also increasing total soil carbon through added biochar carbon, microbial transformation, and carbon fixation processes.
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