WHAT THE EVIDENCE SAYS
Researchers developed an oxygen-isotope method to quantify microbial extracellular polymeric substances across a national-scale survey of Chinese cropland soils. Production rates were comparable to microbial cellular residues and were statistically associated with mineral-associated organic carbon. In carbon-labeling microcosms, extracellular-derived carbon entered the mineral-associated pool at rates comparable to or greater than carbon from cellular residues.
WHY IT MATTERS / OUR READ
The soil-carbon story is becoming less about a single pool of dead microbial biomass and more about multiple microbial pathways into persistent mineral associations. That matters for models and monitoring because a mechanism can be quantitatively important even when it is largely invisible to the proxy we usually measure.
CAVEATS / UNCERTAINTY
The national survey establishes associations and the incorporation experiment was conducted in microcosms. The study identifies a mechanism; it does not yet establish a field-management practice that reliably increases durable carbon storage, nor does it show that boosting extracellular polymers would produce net ecosystem carbon gains.
SOURCE
Nature Geoscience
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