Effect Of Seed Abortion And Predation Level On Seed Quality And Seedling Establishment In Rare Psammophyte Astragalus Lehmannianus(Fabaceae)

Astragalus lehmannianus Bunge.,a rare and endangered?IUCN?psammophytic herb,is narrowly and patchyly distributed in fixed and semi-fixed sand dunes in the Gurbantunggut Desert in China.Natural populations of this species 1)are small;2)set low numbers of seeds per flower;3)experience high insect seed predation;and 4)contain very few seedlings.These characteristics indicate that this species has low regeneration potential.To explore the factors that affect the natural regeneration of A.lehmannianus populations,seed production and factors that influence germination and seedling growth were studied under both field and laboratory conditions.Results revealed some of the causes of endangerment and provided protection strategy for this species.The main results and conclusions are as follows:?1?In natural populations,more seeds were matured at the base of a fruit than at the tip?stigma end?.Neither xenogamy,resource addition nor their combination increased seed set or seed mass at different ovule positions in the fruit.Under different treatments,the proportion of mature seeds decreased from the base to the stigma end of the fruit.?2?This species has a water-impermeable seed coat?physical dormancy?,and scaried?to break dormancy?seeds germinated best at high temperatures.Sixteen to 22%of the seeds were predated by larvae of Etiella zinckenella?Lepidoptera:Pyralididae?.Scarified and low,medium and high predated seed,but not intact seeds,imbibed water readily and germinated to high percentages.With different amount of predation on the same part of the seedling,the rank order of survival percentage,relative growth rate(RGR,mg mg^-1d^-1)and total biomass of the seedlings was:nonpredated?intact?=low predated>medium predated>high predated;and for the same amount of predation on different parts of the seedling,it was intact seedling=cotyledon>radicle>cotyledon+radicle.The pattern of seed abortion in fruits of A.lehmannianus was selective,and it occurred mainly at the stigmatic end of the fruit.This pattern influenced by genetic factors.Theoreticaly,selective seed abortion allows the mother plant to allocate more resources to the non-aborted seeds,and improve seed quality,thereby promoted regeneration potential.Predated seeds are nondormant and can imbibed water rapidly under sufficient water condition,and significantly advance the time of seed germination.Although,low predation has little effect on the survival and growth of seedlings,it can increase the sibling competition caused by predated seeds germinated simultaneously.Medium/high-damaged cotyledons,radicles and cotyledons+radicles can seriously affect the survival and growth of seedlings,thus insect seed predation hinders natural regeneration of A.lehmannianus.