Assessing past water availability using phytoliths from the C4 plant Sorghum bicolor: an experimental approach.

Abstract

Water availability and water management systems were critical for the success of past agricultural societies. One way to determine past water availability is through phytolith ratios as demonstrated by research conducted on modern C3 plants. In order to determine if phytolith ratios in C4 plants are similarly affected by plant water availability, the C4 plant Sorghum bicolor was experimentally grown at three different crop growing stations over a two year period in Jordan. The husks, leaves and stems of the plants grown under the 0% and 100% irrigation regimes were processed and analysed for their sensitive to fixed form phytolith ratio. These results were then compared to results of those conducted using C3 plants. Our results showed that while there were differences in ratios between growing years and the crop growing site, the greatest difference in the ratios was in irrigation regime. Our results also showed, however, that the ratio of sensitive to fixed forms for the samples taken from the husks was far higher than the ratios found in the leaves and stems and far higher than those found in previous studies on C3 grasses. We suggest that if this method is to be used to interpret archaeological phytolith assemblages, an assessment of the likely taxa and plant part composition of the assemblage should first be undertaken through phytolith and macro-botanical analysis.