An isozyme study of clone diversity and relative importance of sexual and vegetative recruitment in the grass Brachypodium pinnatum

Abstract

We asked whether differences in abundance and seed production of Brachypodium pinnatum after 16 yr of four different experimental land use regimes were reflected in differences in vegetative dispersal distance, clone diversity, clone area, and the proportions of sexual and vegetative recruitment. Mean vegetative dispersal distance was 5.5 mm yr-1. Electrophoresis of 5 polymorphic isozyme loci of 20 tillers sampled at defined positions in each of twelve 1 x 6 m sampling areas (3 per treatment) revealed considerable clonal diversity. Per sampling area we found on avarage 9.98 enzyme phenotypes (clones), mean Simpson index was 0.825, and mean Shannon index 0.801. The mean ratio of sexual vs vegetative recruitment was about 1:32 000. Despite this low ratio, clonal diversity within the population of B. pinnatum was higher than reported for other clonal plant populations, possibly because of its high ramet densities. Mean clone area was 5.73 m2 i.e. mean clone radius was 1.35 m. None of the 10 pairwise correlations between abundance and seed production on the one hand, and number of clones per plot sample, plot Simpson index, plot Shannon index, ratio of vegetative vs sexual recruitment, and clone area on the other, was significant. Mean clone radius was 245 times larger than the mean distance of yearly vegetative dispersal which suggests old ages and low turnover rates of clones. The time scale of the inert response of clonal diversity of B. pinnatum to changes in land use appears to largely exceed the experimental period of 16 yr.