Genetic diversity of populations of "Brachypodium pinnatum" (L.) P. Beauv. : expansive grass in a fragmented landscape

Brachypodium pinnatum belongs to native grasses which could dramatically decrease the biodiversity of calcareous grasslands, therefore, an examination of the mechanisms of its expansion is of prime importance for their conservation. We studied the genetic structure of 12 subpopulations of the expansive grass B. pinnatum in a heterogeneous landscape with AFLP markers, aiming at determination whether spatial isolation influences the genetic diversity and the population genetic structure of this species. A high level of overall (79%) and within population polymorphic loci (38–44%) were found and 220 different genotypes were distinguished among the 252 samples analysed. No significant population structure nor isolation-bydistance were found, despite their long-time fragmentation history. This confirms that isolation of calcareous grasslands in a landscape cannot prevent the expansion of B. pinnatum grasses because of the high generative dispersal ability. Subsequent quick and extensive clonal growth of this species enables the successful establishment. In most cases mowing or grazing is sufficient to keep this species at a low density within ancient grasslands and to prevent seed and pollen dispersal, but not for restoration of species-rich calcareous grasslands