Natural Regeneration And Samara Characteristics Of Endemic Acer Griseum(Franch.) Pax

As one of China's endemic and endangered species, Acer griseum is a wonderfulornamental and timber species. It is cultivated and planted in world famous botanical garden,such as Kew Gardens, while seldom planted in our home gardens. Researches on it at homeand abroad are nearly blank except only on its propagation until now. Natural distribution,habitat, soil seed bank and natural regeneration were investigated in order to elucidate thecauses for the decrease of natural populations. Phenotypic variation of samara from differentpopulations was observed and analyzed to explore its geographical variation pattern and thecorrelation with geographical and climatic factors. Causes for seed dormancy was studied bysulfur treatment and water absorption curve experiment. It is aimed to provide the scientificand theoretical basis for conservation of genetic resources, cultivation and utilization of Acergriseum. Meanwhile it will fill the research gap of Acer griseum at home and abroad. Theresults are as follows:1. The natural distribution of the species is centered in Central China occurring in wetmountain vegetation zones, including subtropical evergreen mixed hardwood forest and warmtemperature hardwood forest. It is a sub-climax species and an associated tree species, whichscattered in the mountain broad-leaved mixed forest, the mountain coniferous and broad-leavedmixed forest in addition to the mountaintop shrub forest. It grows in middle and highmountains mainly ranging between1000and18000m in the altitudinal distribution. Thespecies occurs mostly on semi-sunny slopes, semi-shade slopes, shade slopes and gullies. Itgrows on the mountain brown soil, yellow brown soil and mountain cinnamon soil. Thethickness of soil layer from the bare rock to about30cm in depth, some even grows in rockcrevices.2. It naturally regenerated mainly by seed with the stump-sprouting and root suckers.Most of the seeds in soil seed bank were kept in the litter. Field survey found that there were 172seedsï¹'m-2in the litter, while only42seedsï¹'m-2between0to10cm in soil layer. Few orno seeds were kept in deeper than10cm soil layer. The amount of seeds was negativelycorrelated with the distance from the parent tree and the wind also can contribute to seeddispersal.3. The rich genetic diversity in morphological traits of samara of Acer griseum existed inwild populations. Variance analysis showed that the difference of samara length, samara width,samara volume,samara surface area and1000-seeds weight were significant among the7different populations. Coefficient of variation of every characteristics showed big differencesamong the different populations. The morphological characteristics was closely correlated withthe geographic longitude, latitude, altitude and annual average temperature. The morphologycharacteristics of the maple samara displayed geographic variation by long term environmentimpact.4. The water-absorption by the seeds of A. griseum was a slow process due to its thickwoody pericarp. Water content of seeds of A. griseum reached only68%after140hs ofwater-absorption treatment. The sulfur treatment for3hs did not speed up the water-absorption,but made the pericarp thinner without damaging seed viability. The main reason for seeddormancy of A. griseum was physiological dormancy of seed embryo and physical obstacle ofthe pericarp. How to make the hormone reaching the seed embryo through the compactpericarp was critical to break its dormancy quickly.All the above results indicated that reduction of the quantity of A. griseum wild resourcesmay be due to bad habitat, low productivity and high rate of seedless samara, difficulty in seedgermination, as well as the poor habitat where natural regenerated seedlings grow.