5) Dr. Ofir Katz

Amongst other traits, grasses are known to actively take up and accumulate silicon, which plays multiple roles in their biology including protection from aridity and herbivory. However, the variations of plant and grass silicon concentrations along environmental gradients are poorly understood, with conflicting evidence from different regions and species. One possibility is that phenotypic plasticity drives higher silicon concentrations in rainier locations owing to greater transpiration that allows passive (and thus less costly) silicon uptake. Conversely, populations in more arid locations may represent more silicon-rich ecotypes, owing to selection for this trait as an adaptation to aridity and grazing. A study of the grass Avena sterilis in Israel indicates a possible U-shaped curve, with lowest silicon concentrations in intermediate sites. This suggests that ecotypic differentiation is a stronger driving force in more arid locations whereas phenotypic plasticity dominates in rainier locations. Comparable pattern, or any consistent patterns, is not observed in non-grass species, compatible with no selection in favor of silicon uptake in arid locations or of phenotypic plasticity. In this talk, I discuss the evidence, possible explanations and the challenges in devising a clear model to explain these variations.