Mitigating the potential contamination risk incurred in sampling herbarium specimens for phytolith reference collection

Abstract

Phytoliths are emerging as a critical paleoenvironmental and archaeological proxy record in a variety of landscapes. These non-organic objects preserve well in both terrestrial and lacustrine sedimentary contexts. Creating a local reference collection is a crucial step for contending with the multiplicity and diversity of phytolith forms, but previous authors have noted a potential problem with one of the most common methods for extracting phytoliths from fresh and herbaria specimens, the dry-ashing method. This method incurs a contamination risk in the muffle furnace during ashing. The standard weight of plant tissue for extraction is relatively high (200 mg) when considering the amount of material accessible in herbaria collections. We devised the following experimental study to test the contamination potential of our muffle furnace, and the possibility of using a smaller weight of plant tissue (100 mg) to derive the same results and reduce potential risk. The results of this study indicate that reducing the initial plant material by half the weight will result in a slightly lower contamination risk and equivalent diversity of morphotypes in the final phytolith sample. Therefore, we argue that reducing the plant tissue will enable a less costly use of herbaria material and a lower chance of inter-sample contamination.