Highly variable clonal diversity and spatial structure in populations of sickle medic

Abstract

Abstract Clonal diversity and spatial structure in six remnant Estonian populations of sickle medic Medicago sativa ssp. falcata growing in different habitat conditions were estimated at three different spatial scales, in 1 m 2 and 4 m 2 small-scale plots and in 30–60 m long linear transects, using four polymorphic isozyme markers. Sampling all ramets in fourteen 1 m 2 quadrates yielded 419 ramets which displayed 113 multilocus genotypes (MLGs), whereas 311 ramets from 4 m 2 plots exhibited 144 genets and 262 ramets in six transects revealed 223 genets. All MLGs except two were distinct, indicating extremely high genotypic diversity and strong differentiation among populations. Highly variable small-scale spatial structure with adjacent ramets of identical MLGs and different sizes was detected in quadrates up to monoclonality of some plots. Differences in local disturbances and land-use history of populations were found to be associated with their variable genotypic structure and diversity. Sexual reproduction was locally suppressed in abandoned grassland at places with a dense cover of competing grasses and thick litter layer, however, still occurring in suitable or disturbed places. Strong competition at sites densely covered with adult plants has led to the local elimination of small clones and preferential spread of survived clones. High clonal richness observed in long transects with up to 100% consisting of unique MLGs suggests ability of sickle medic for repeated sexual reproduction in established populations. Local disturbances are supposed to provide suitable microsites for seedling recruitment, evidenced by the presence of unique and small MLGs of recent origin.