Background
The authors write that "one of the most promising biogeochemical carbon sequestration mechanisms is the occlusion of carbon within phytoliths, the silicified features which are deposited within plant tissues (Parr and Sullivan, 2005; Song et al., 2012a, b)." And in support of this claim, they note that (1) "phytolith-occluded carbon (PhytOC) is found in many plant species (Parr et al., 2010; Parr and Sullivan, 2011; Zhuo and Lu, 2011), that (2) it "is highly resistant to decomposition (Wilding, 1967; Mulholland and Prior, 1992; Parr and Sullivan, 2005)," and that (3) it "may represent up to 82% of soil carbon (Parr and Sullivan, 2005)."

What was done
Using a phytolith content-biogenic silica content transfer function obtained from their study, in combination with published silica content data and aboveground net primary productivity data pertaining to the leaf litter and herb layers of China's forests, Song et al. were able to estimate the production of phytolith-occluded carbon in China's forests.

What was learned
Based on their approach to the problem, the four Chinese researchers determined that "the present annual phytolith carbon sink in China's forests is 1.7 ± 0.4 Tg CO2 per year, 30% of which is contributed by bamboo because the production flux of PhytOC through tree leaf litter for bamboo is 3-80 times higher than that of other forest types." And they additionally note that "recent studies reveal that fine plant roots may also contain a certain amount of silica (Ding et al., 2008) and are rapidly recycled (Gu et al., 2011)," which suggests, in their words, that "the phytoligh carbon sink in this study may be underestimated."

What it means
The ultimate take-home message of Song et al., as expressed in the concluding sentence of their paper's abstract, is that "forest management practices such as bamboo afforestation and reforestation may significantly enhance the long-term terrestrial carbon sink and contribute to mitigation of global climate warming."

References
Ding, T.P., Zhou, J.X., Wan, D.F., Chen, Z.W., Wang, C.Y. and Zhang, F. 2008. Silicon isotope fractionation in bamboo and its significance to the biogeochemical cycle of silicon. Geochimica et Cosmochimica Acta 72: 1381-1395.

Gu, J., Yu, S., Sun, Y., Wang, Z. and Guo, D. 2011. Influence of root structure on root survivorship : an analysis of 18 tree species using a mini-rhizotron method. Ecological Research 26: 755-762.

Mulholland, S.C. and Prior, C. 1992. Processing of phytoliths for radiocarbon dating by AMS. The Phytolitharien Newsletter 7: 7-9.

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

Parr, J.F. and Sullivan, L.A. 2011. Phytolith occluded carbon and silica variability in wheat cultivars. Plant and Soil 342: 165-171.

Parr, J.F., Sullivan, L.A., Chen, B. and Ye, G. 2010. Carbon bio-sequestration within the phytoliths of economic bamboo species. Global Change Biology 16: 2661-1667.

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: 3647-3653.

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 153: 319-331.

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

Zuo, X. and Lu, H. 2011. Carbon sequestration within millet phytoliths from dry-farming of crops in China. Chinese Science Bulletin 56: 3451-3456.