Evidence of old soil carbon in grass biosilica particles

International audiencePlant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system , claims were recently made that phytoliths from grasslands play a significant role in atmospheric CO 2 sequestration. However, anomalous phytC radiocarbon (14 C) 5 dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements (14 C and δ 13 C) of phytC, plant tissues, atmospheric CO 2 , and soil organic matter. State-of-the-art methods assured phytolith purity, while sequential stepwise-combustion revealed complex chemical–thermal decomposability properties of phytC. 1