Breeding system and its consequence on fruit set of a rare sand dune shrub Eremosparton songoricum (Fabaceae: Papilionoideae): implications for conservation

The breeding system and its consequence on fruit set of Eremosparton songoricum (Litv.) Vass., a rare shrubby legume occurring in moving or semi-fixed sand dunes of Central Asian deserts, were examined by manipulative experiments and observational studies in natural populations during the period of 2007-2009. The results showed that E. songoricum exhibits a mixed mating system. It is self-compatible, but depends strictly on pollinators to set fruits. Only two effective pollinators were detected and they triggered the specialized pollination mechanism (a 'brush type' and 'tripping mechanism'). Geitonogamy becomes predominant in natural populations, because (74.5 plus or minus 1.3)% of visiting activity happened within or between inflorescences and (24.3 plus or minus 1.4)% occurred between ramets. As a result, inbreeding depression caused by geitonogamous selfing inevitably happened under natural conditions, showing 2.36 times less fruit set than was achieved by hand cross-pollination. The results explained the rarity of the species due to its breeding system, and will assist to develop suitable conservation strategies in severe desert environments.