Germination ecology of the clonal herb Knautia arvensis: Regeneration strategy and geographic variation

Abstract

We investigated germination responses and seed recruitment in the clonal grassland herb Knautia arvensis (Dipsacaceae) throughout its distributional range in Norway. Four predicted relationships between germination responses and field regeneration behaviour were tested using phytotron experiments and experimental and observational field studies. Seedlings appeared in all experimental microsites in the field, corroborating phytotron predictions that gap- or depth-sensing strategies should be absent in the species. Seasonal timing patterns were predicted from a cold stratification response in the phytotron, but these were not supported in the field. The relationship between dormancy, germinability during storage, and seed carry-over in the field largely conformed to expecta- tions. Seeds from four different geographical regions responded differently to temperature and cold stratification and storage. Dormancy and seed carry-over was higher in seeds from a coastal population, where winters are relatively mild and the probability of repeated freeze-thaw events is high, than in populations from mountain and inland areas, where winters are colder. This is discussed against two alternative hypoth- eses about the relationship between climate and dormancy in seasonal climates.