Germination characteristics of old seeds help explain coexistence of selected dry grassland species

Résumé Fr

Coexistence of congeneric dry grassland species presents an interesting opportunity to evaluate traits of closely related co-occurring species. Coexisting congeneric species, exhibiting common traits, are expected to experience strong niche-overlap, which can intensify competition. Mechanisms that enable coexistence should also reduce competition. We assume that plant characteristics differing among coexisting species would diminishing interspecific competition and therefore enable coexistence. We were interested in the species characteristics of three congeneric pairs found in the same sub-Mediterranean montane grassland (the Karst region in Slovenia) : Anthyllis montana var. jacquinii, Anthyllis vulneraria, Gentiana clusii, Gentiana verna ssp. tergestina, Plantago holosteum and Plantago media and an additional four accompanying common species. We compared their morphological and reproduction traits as recorded in the literature. We performed germination studies with seven-year-old seeds and compared germination rate under various conditions. Old seeds of A. montana var. jacquinii, A. vulneraria, Lotus corniculatus, Coronilla vaginalis, P. holosteum and Centaurea rupestris were able to germinate. Clustering analysis (k-means clustering) on traits and germination data resulted in two clusters, which produced ecologically interpretable patterns. Congeners were always found in separate clusters. Analysis showed the most prominent difference between clusters was germination rate at low temperatures. Results showed that, because of the high germination rate of old seeds in Anthyllis congeners, they have the potential to form longterm persistent seed banks, whereby the germination rate in the rarer congener was lower. Between Plantago congeners, the rare species exhibited the potential to be persistent in soil seed banks, however, only in the presence of unfavorable germination conditions. Seeds from both Gentiana congeners were shortlived rather than dormant. Studying coexisting species that occupy similar niches is becoming increasingly important, since the possibility for competitive, ecologically similar species to meet increases along with the range changes caused by global climate change.