Studies On Evolutionary Ecology Of Seed Size Variation In The Eastern Qinghai

Seed size is an important feature of the attribute constellation of a plant species. Under the pressures of long-term selection and evolutionary, most plants have different seed size to adapt to the habitat and ensure the viability of offspring. As an important biological character in botany and ecology, seed size has relationship with other characters of plant life history, including dispersal capacity of seed, life form, plant individuals in a community, the trait of seed germination, seeding livability, the dispersal mode of seed, etc. In this study, the fresh seed size of 1130 angiosperm species which belong to 412 genera in 106 families were collected from the eastern Qinghai-Tibet plateau. We examined the pattern of the seed size variation in the flora, the relationship of seed size with phylogeny, areal-types of plants, dispersal mode, growth form, plant height, perenniality, fruit type, onset of flowering, duration of flowering, habitat and altitude.The results were shown:1. Within the flora of eastern Qinghai-Tibet plateau, the frequency of seed size classes on a log scale produced a normal distribution.The seed size is ranged from 10-3 to 104mg, which has 6-7orders of magnitude.In addition, the mostly seed size is mainly concentrated from 0.1 to 10.0mg, which hold 70.53%.Especially large or small seeds are very scarce in the flora. So we consider that small seed is preponderant on the eastern Qinghai-Tibetan Plateau.2.Seed size was strong related to phylogeny. Class, order and family membership accounted for most of the variation in log seed size(11.6%,31.4%and 58.2%, respectively).Therefore, the seed size variation was determined mainly by the phylogeny.3.From whaterever taxonomic levels, seed size variation showed no consistent direction of evolution or evolutionary model.Generally, the seeds near the base of APGâ…¡system are likely to be in the middle size. Trends in the evolution of seed size has gone in many directions,towards larger or smaller seeds.Thus, the seed size of angiosperm has the obvious characteristics of adaptive radiation.4.With different areal-types of plants, the seed size variation is significant difference. The primitive families and genera have the larger seeds, and the more evolved families and genera have the smaller seeds relatively in general.5.Seed size was correlated with many other plant attributes such as dispersal mode, growth form, plant height, perenniality, fruit type, onset of flowering and duration of flowering, respectively,even in after phylogenic effect. The strongest of the plant attributes in seed size are fruit type, and dispersal mode, followed by plant height and growth form.6. Seed size variation is also significantly associated with vegetation types.The mean log scale seed size from large to small in different vegetation types is forests, shrubs, cultivated vegetation, steppes and medows, aquatic vegetation, open vegetation on flowing rock hillside, cushion vegetation and swamp vegetation.7. There is significantly negative relationship between the variation in seed size and altitude in the flora, and seed size decreases with altitude on the whole.But one interesting phenomenon is that the seeds with middle size are distrbuted at 3100m, and seed size becomes to larger or smaller respectively along with the altitude increasing or decreasing respectively. That is to say, the seed size has the evolutionary pattern of adaptive radiation.8.The effect of altitude on seed size variation has different patterns among dispersal modes, areal-types of plants, growth forms, fruit types, different plant height, different perennialities, vegetation types, families, and even among species in a family. But there is a commen feature:from every aspect to examine effect of altitude on seed size variation, it seems that the seed size has a vertical distribution implications of adaptive radiation. That is, taking the altitude of 3100m as a starting point, the seed size becomes to larger or smaller respectively along with the altitude increasing or decreasing respectively.