Decade-Long Soil Warming Study: Deep Particulate Carbon Is Vulnerable, Mineral-Bound Carbon Holds

A 9.5 year soil warming experiment at Blodgett Forest in California's Sierra Nevada foothills found that deep subsoil particulate organic carbon is far more vulnerable to warming than mineral-associated organic matter. After heating soil to 4 degrees Celsius above ambient down to one meter, researchers measured sharp declines in free and occluded particulate carbon at 80 to 90 centimeters, while mineral-bound carbon showed no significant change at any depth. The results suggest that models treating soil carbon as a single pool may miss where warming losses actually occur. The study, published in the journal SOIL, used density fractionation and infrared spectroscopy to separate and characterize soil carbon fractions. Topsoil and mid-depth carbon held steady, likely because fresh root inputs replenished what microbes consumed, but the deep soil had little new carbon coming in. That distinction matters for climate modeling and for any project that relies on soil carbon staying put over decades. Future warming experiments need to focus on subsoils and specific carbon fractions, not just bulk soil totals.