Background
Phytoliths are microscopic pieces of silica that form in the cells of many kinds of plants, which in the words of the authors "usually occlude 1-6% of C (phytolith-occluded carbon, PhytOC)," as reported by Piao et al. (2009) and Song et al. (2012a,b). And this PhytOC, when protected by silica, is, as they note, "highly resistant to decomposition (Wilding, 1967; Wilding et al., 1967; Mulholland and Prior, 1992; Parr and Sullivan, 2005)." And so well does silica perform this important ecosystem service, the authors say "it has been reported that the age of phytoliths in soils and sediments can be older than 8000 years," which can lead to their providing "15-37% of long-term biogeochemical C sequestration," as per the findings of Parr and Sullivan (2005).

What was done
In a recent study of this phenomenon, Song et al. "constructed a silica-phytolith content transfer function and calculated the magnitude of the phytolith C sink within China's croplands," where "calculations were performed using relevant crop data such as land productivity, the Si-rich organ ratio, silica and PhytOC content, and the PhytOC stability factor."

What was learned
The four researchers report that the phytoliths sequestered in the croplands of China - which represent approximately 18% of the world's croplands - currently remove about 4.39 ± 1.56 Tg of CO2 per year from the atmosphere.

What it means
Song et al. conclude the report of their work by noting that their data indicate that "beneficial cropland management practices such as rational irrigation and fertilizer application, and crop pattern optimization may be taken to further enhance the phytolith C sink in croplands," to the extent that "global climate change could be partially offset by increasing cropland phytolith C sequestration at both a national and global scale."

References
Mulholland, S.C. and Prior, C. 1992. Processing of phytoliths for radiocarbon dating by AMS. Phytolithar. Newsl. 7: 7-9.

Parr, J.F. and Sullivan, L.A. 2005. Soil carbon sequestration in phytoliths. Soil Biology and Biochemistry 37: 117-124.

Piao, S., Fang, J., Ciais, P., Peylin, P., Huang, Y., Sitch, S. and Wang, T. 2009. The carbon balance of terrestrial ecosystems in China. Nature 458: 1008-1013.

Song, Z., Liu, H., Si, Y. and Yin, Y. 2012a. The production of phytoliths in China's grasslands: implications to biogeochemical sequestration of atmospheric CO2. Global Change Biology 18: 1647-1653.

Song, Z., Wang, H., Strong, P.J., Li, Z. and Jiang, P. 2012b. Plant impact on the coupled terrestrial biogeochemical cycles of silicon and carbon: implications for biogeochemical carbon sequestration. Earth-Science Reviews 155: 319-331.

Wilding L.P. 1967. Radiocarbon dating of biogenetic opal. Science 156: 66-67.

Wilding, L.P., Brown, R.E. and Holowaychuk, N.N. 1967. Accessibility and properties of occluded carbon in biogenic opal. Soil Science 103: 56-61.