Geographical and land-use effects on seed-mass variation in common grassland plants

Abstract

Seed mass is one of the most important plant traits. It is strongly related to plant fitness and life-history strategy, and is one of the key determinants of the ability of plants to spread and thus to respond to changing environments. While substantial empirical work has been devoted to understanding seed-mass variation across species, we know less about seed-mass variation within species, its geographical and ecological differentiation, and the degree to which it is influenced by environmental change. Here, we studied intraspecific variability in seed mass of six common grassland plants (Arrhenatherum elatius, Bromus hordeaceus, Cerastium holosteoides, Heracleum sphondylium, Trifolium repens and Veronica chamaedrys) across three regions in Germany and a broad range of land-use types and intensities. We found substantial seed-mass variation among regions, populations, and individuals within all of the studied species. In five species, seed mass had a strong and consistent geographic component, and in three species we found significant effects of land use – fertilisation, grazing intensity or mowing frequency – on seed mass. In several species, land use and geographic region not only affected mean seed mass, but also the variability of seed mass within populations. Our study demonstrates that seed mass is geographically and ecologically differentiated in common grassland species. It is likely that both phenotypic plasticity and genetic factors contribute to this differentiation. Our results also show that seed mass is a highly variable trait with typically around 10-fold variation within species.