Inter-population variability in seed dormancy, seed mass and germination in Helianthemum salicifolium (Cistaceae), a hard-seeded annual herb

Abstract

Many plant traits show variability within species in response to ecological gradients. In this study, we examined the variability in seed traits among ten populations of Helianthemum salicifolium (L.) Miller in Anatolia, Turkey. Since the Anatolian Peninsula has a geographic structure exhibiting longitudinal, elevational and climatic gradients, we hypothesized that seed dormancy, seed mass and germination show inter-population variability. We also postulated that seed traits are correlated to climatic and geographic characteristics of the populations. Since H. salicifolium is a species with a hard seed coat, we conducted germination experiments using heat shock and mechanical scarification. The germination percentage was improved significantly by mechanical scarification but remained unaltered by heat shock treatments in all sampled populations. As expected, seed traits exhibited substantial variation among the populations. We found no association between germination traits (dormancy level and germination rate in different treatments) and environmental variables. By contrast, seed mass showed an elevational/longitudinal/climatic pattern: Populations in cooler and higher-elevation areas had larger seed mass. However, when the influence of climate was controlled, the geographic location became an important factor affecting seed mass. We conclude that seed mass variation among populations of H. salicifolium in Anatolia is shaped by the climate at the regional scale, but at the same time, geographically closer populations exhibit more similarity in seed mass.