Seed Germination And Dormancy In An Alpine Meadow On The Eastern Qinghai-Tibet Plateau

Since the days of Theophrastus (372-287 B.C.) , a vast amount of information related to seed germination has accumulated. However, most of the literature investigated seed germination within one species, and the less paid attention to the difference among species. Furthermore, most comparison in seed germination among species only limited to compare among several species or within a genus, and the comparative studies on seed germination and dormancy in a whole community were much less. But the comparative results derived from one or several species didn't account for the ecological significance of seed germinability. In addition, the studies reported on seed germination within a community were done in tropical or temperate zone, and there was not investigation on alpine meadow. Thus, we investigated the seeds germinability of species in an alpine meadow on the eastern Qinghai-Tibet plateau, which might be the important supplement to the field on inter-specific seed germinability. We expected to provide the basic theoretic evidence by our study on discuss the species composition and dynamic of ecosystem in the alpine meadow on the eastern Qinghai-Tibet plateau.The results showed: 1) Among the studied 633 species, 66 species did not germinate, over half of the species were dormant, and physiological dormancy was the most important; according to the seed germination characteristics, the species were divided into 4 distinct groups: rapid, slow, intermediate (percent germination > 50%) and low germinating(percent germination <50%). 2) There was significant difference in percent germination among altitudes, but not significant in days to first germination and dormant proportion of species; and there was significant negative correlations between percent germination and altitudes. 3) There was not significant difference in seed germinability and dormant proportion of species among habitats, however, species from south slope had the highest percent germination, the earliest days to first germination and the lowest dormant proportion of species, and species from north slope had the highest dormant proportion of species. 4) There was significant difference in seed germinability among life form, perenniality and seed dispersal mode. The woody plants had the lowest percent germination and the highest dormant proportion, and the graminoid plants had the adverse results; the annuals had higher dormant proportion and lower percent germination; increasing percent germination and decreasing dormant proportion were going with increasing dispersal; 5) There was significant negative correlation between percent germination and seed size, and significant positive correlation between days to first germination and seed size; 6) There was significant difference among families. Furthermore, there was a trend that most species with lower dormant proportion were concentrated in families in the upper portion of the phylogenetic tree, and most species with higher dormant proportion were in the lower position of the phylogenetic tree; 7) In summary, phylogenetic relatedness had the greatest contribution to the variation in mean germination time (25%), and all the life-history traits could explained only 7% of the variation in mean germination time among the species in the alpine meadow. In addition, there was significant interactions between phylogenic groups and altitudes (or habitats), which could be considered that the phylogenetic constraints on seed germinability also related to environment conditions. Thus, seed germination and dormancy in the alpine meadow on the eastern Qinghai-Tibet plateau were affected by phylogenetic, life-history and environment factors. The ecological and phylogenetic factors should be taken into account when we discussed the difference of species.