Plasticity and variability in the patterns of phytolith formation in Asteraceae species along a large rainfall gradient in Israel

Silicification and phytolith formation in Poaceae species growing in arid and semi-arid regions are commonly thought to be positively correlated with silica and water availabilities and with transpiration. To expand our understanding of this phenomenon, we chose to study species of the Asteraceae, the largest dicotyledonous family. We measured phytolith concentrations in eight Asteraceae species (three non-spiny and five spiny) and one Poaceae species (Avena sterilis), as reference, along a large climatic gradient of 80-900. mm mean annual rainfall in Israel. Phytolith concentration in A. sterilis was found to be positively correlated with water availability and with a minor effect of soil silica availability. The three non-spiny Asteraceae species have a partially similar pattern of changes in silicification according to water availability in more humid habitats, but with higher phytolith concentrations in the most arid site. The five spiny Asteraceae species have various patterns of phytolith formation, not consistently related to water and soil silica availabilities. These results demonstrate that patterns of phytolith formation in the Asteraceae differ among taxa and also from the situation in grasses.