Comment on "Possible source of ancient carbon in phytolith concentrates from harvested grasses" by G. M. Santos et al. (2012)

[摘要] Santos et al. (2012) address the important issue that ¹⁴C dating of thecarbon occluded in silica phytoliths (PhytOC) isolated from contemporaryplant materials can produce ages that are incompatible, being often severalkyr older, with both their known recent origin and the ¹⁴C age of thebulk plant material. In their article, Santos et al. (2012) propose that theanomalously old ¹⁴C carbon dates of PhytOC from harvested plantmaterials are based on plants taking up "old" dissolved soil carbon to theplant by roots during nutrient uptake. They then propose that this oldsoil-derived carbon is subsequently partitioned from the general plantbiomass into either the silica phytoliths they produce or as recalcitrantorganic matter elsewhere in the plant. We suggest that the full dataavailable for PhytOC ¹⁴C dating do not support this hypothesis. Santoset al. (2012) also address the important issue of contamination of PhytOC bygeneral plant biomass material that can occur with procedures thatincompletely extract phytoliths. Whilst we agree that such contaminationneeds to be avoided when examining the nature of PhytOC, we also point outthat the converse problem, i.e. removal of PhytOC by over-vigorous extractionprocedures, can also have important adverse consequences.

[学科分类] 地球化学与岩石