MECHANISMS FOR RECRUITMENT AND POPULATION GROWTH IN NERVILIA NIPPONICA, AN ENDANGERED ORCHID IN JAPAN

Abstract

Elements of the recruitment cycle of Nervilia nipponica, an endangered terrestrial orchid endemic to Japan, were examined towards the development of a conservation strategy. Field studies and bagging experiments indicated that the species is capable of outbreeding but is habitually autogamous and therefore not pollinator-limited for seed set under natural conditions. Although seeds harvested from open-pollinated capsules exhibited a mean germination percentage of over 70 when cultured in vitro, germination of seeds from the same capsules was variable and averaged just 0.5% following burial in the soil in seed packets at the source populations. A demographic study of marked tubers revealed a strong capacity for vegetative propagation. The affects of these processes on spatial genetic structuring were examined using AFLPs. Limited diversity was found within the species as a whole, and one intensively sampled population was found to harbour just two distinct, possibly clonal genotypes. Despite iterative inbreeding, most seed is viable and may be widely dispersed. Subsequent recruitment appears to occur through vegetative propagation. Rarity in N. nipponica may be associated with limited recruitment from seed resulting from heterogeneity in soil microsite conditions. Conservation is most likely to be effective if targeted at habitat management for seed germination and genet persistence.