Carbon concentrations in phytoliths and carbon sequestration in soil
In recent years there has been much work on the possibility that carbon could be sequestered in phytoliths and contribute to solving global warming.1, 2 There have been a number of calculations of how much is sequestered globally. The crucial figure in these calculations is the concentration of carbon in the phytoliths that is used, so-called phytolith occluded carbon. These figures are derived from phytoliths that have been acid digested or dry ashed at 450-500oC. Values vary from less than 0.1% to 6% depending on the technique used. But are any of these measurements realistic? In native unprocessed material the lemma macrohair from Phalaris canariensis contained 40% silica, 55%, polysaccharides and 5% proteins.3 At maturity these hairs consist entirely of wall material. I know of no data for lumen deposits, which undoubtedly have a higher percentage silica in the native state. Some of the carbon in both cell wall and lumen phytoliths cannot be accessed by hot acid or dry ashing. I suspect that more carbon is inaccessible to breakdown processes in soil than is estimated by our “occluded carbon” determinations. My question is whether these measurements are a good estimate of what is present in soil phytoliths?