Distribution Of Rare Psammophyte Asrtragalus Lehmannianus(Fabaceae) And The Effect Of The Cocoon-shaped Calyx On Sexual Reproduction And Seed Disperal

Astragalus lehmannianus Bunge., a rare psammophyte Fabaceae herb, is only distributed in fixed and semi fixed sand dunes in the Gurbantunggut Desert of Junggar Basin in China. This species was listed one of the first batch of key protection plants in Xinjiang. The shape of synsepalous calyx looks like a cocoon. The geographic distribution, community feature and endangered status of A. lehmannianus were analyzed by the examination of herbarium specimens and references, field observation and controlled experiments in this thesis. At the same time, the role of cocoon-shaped calyx of this species in reproductive success, seed dispersal and defense were observed and analyzed. These results will not only provide basic data for the red list of endangered plant species of IUCN, but also can offer theoretical materials for exploring the relationships between the reproduction and population recruitment, revealing the endangered causes and putting forward the protection strategies of this species. The main results and conclusions are as follows:(1) A. lehmannianus is only distributed in the southern marginal zone of the Gurbantonggut Desert in China. There were 0.31±0.17 individuals per 100m2 in six investigated distribution area. The dominant species in communities of six distribution area are Haloxylon ammodendron and Haloxylon persicum mainly, and tree and shrub, perennial herb and annual herb occupied 20.16±4.02% 、 16.97±3.54% and62.85±3.21% of total species, respectively. Mediterranean components and West Asia to Central Asia components were the main distribution type of genera in all communities. Ephemeral annual species was the main component of annual herb. The endangered status of this species is critical endangered [CR B1ab+2ab; C2a(i)].(2) Zebramegilla albigena is the only pollinator of A. lehmannianus and pollination pattern belongs to“valve” mechanism. The taper calyx of this species enclosed the middle and lower part of corolla at the flowering time, and inflated quickly into a cocoon-like structure during the period of flower wilting. Thecocoon-shaped calyx not only provided a landing platform for pollinators at the flowering stage, but alsomaintained the shape of papilionaceous corolla. So it can help visitation of pollinator and increase the chance of cross-pollination. At the fruiting stage, mean daytime temperature inside the calyx was lower than outside the calyx, and mean daytime relative humidity was higher than outside the calyx. These results indicated that the cocoon-shaped calyx can avoid the influence of high temperature on fruit development, and provide a relatively stable microclimate for developing fruit. In the process of seed dispersal, this kind of calyx could increase the buoyancy of dispersal units and make them disperse farther.(3)The most abundant florivore was Mylabris calida Pallas in A. lehmannianus. It could eat corolla,stigama and stamen which stretched out from calyx and decreased the fruit set directly. In addition, this insect species could damage floral structure and affect the visitation of pollinators, and thus reduced cross-pollination. However, the existence of cocoon-shaped calyx of A. lehmannianus can decreased the degree of flowers attacked by insect significantly, and increased the fruit set.These results showed that A. lehmannianus is a critical endangered species. The cocoon-shaped calyx of this species is not only benefit for sexual reproduction, but also can enhance the dispersal ability of seed and defense florivore to eat flower. Overgrazing, land use, engineering construction, tourism and other human activities may be the direct cause to threaten this speceis. However, both inbreeding depression caused by pollinators limitation and the regeneration limitation of population resulting from the extreme desert environment condition and climate change may be the indirect factors that cause this species endangered.