Effects of habitat fragmentation and soil quality on reproduction in two heathland Genista species

摘要

Habitat fragmentation decreases plant population size and increases population iso-lation, as well as altering patterns of plant–animal interactions, all of which mayreduce plant fitness. Here, we studied effects of habitat fragmentation (in terms ofpopulation size and isolation) and soil quality on the reproduction of two rarelegume species, Genista anglica (13 populations) and Genista pilosa (14 popula-tions), confined to remnants of acidic and nutrient-poor Calluna heathlands. Singleindividuals of the Genista plants are impossible to distinguish; population size wastherefore estimated according to the area occupied (referred to as population sizehereafter). We collected soil samples in all heathland sites to determine content ofsoil water, C, N, P, Ca, K and Mg. In both species values of soil pH and C/N ratio,as well as content of soil P and base cations, reflected the highly acidic and nutri-ent-poor environment of the heathlands. Population sizes were unrelated to soilquality. Although the two Genista species are similar in morphology and ecology,effects of explanatory variables on reproduction were largely inconsistent acrossspecies. In G. anglica, population size had a positive impact on all reproductivevariables except germination rate, which, in contrast, was the only variable affectedpositively by population size in G. pilosa. In both species, mean total reproductiveoutput, calculated as the product of total seed mass per shoot and total germina-tion, increased with increasing water content and decreased with increasing P. InG. anglica, we found positive effects of the C/N ratio on all reproductive variablesexcept mean single and total seed mass per shoot. In summary, in both speciesreproductive success per shoot decreased with increasing soil nutrient availability inthe heathland sites. The infestation of two large populations of G. pilosa with thepre-dispersal, seed-predating weevil Apion compactum had no significant effect onreproduction of the populations.