Position-dependent Effect Of Seed And It's Ecological Adaptive Significance In Eremopyrum Distans

Eremopyrum distans (Eremopyrum distans (C. Koch) Nevski.) is an annual ephemeral in Poaceae. It is widely distributed in the Junggar Desert with the spikelets can produce 1-6 caryopsis (hereafter"seeds") but only <1% spikelets produce 4-6 seeds. Seeds of this species can germinate both in autumn and in spring. In this paper, the morphology and imbibition characteristics, dormancy and germination characteristics, seedling growth, plant size and seed output from plants of seeds in positions 1, 2 and 3 of a spikelet which were numbered from the bottom up (were placed in groups 1, 2 and 3, respectively) were studied manipulatively both in field and indoors, the differences among characteristics of three groups were analyzed, and the ecological adaptive significance of seed position-dependent effects in this species was discussed. The main results are as follows:(1)In Eremopyrum distans, seed size and mass decreased significantly as seed position increased.(2)Seeds of three groups were different in imbibition characteristics with the rate of water absorption of group 3 was significantly higher than that of group 1 and 2 .(3)Fresh seeds of three groups were different in depth of non-deep physiological dormancy with group 1>group 2>group3; Seeds of three groups were different in drought resistance during germination stage with group 1>group 2>group3; All seeds of three groups were dead after 3, 4 months of burial, indicating this species could not form persistent soil seed bank.(4)When regularly watered, seeds of three groups all could germinated both in autumn and in spring, while those under natural soil moisture conditions germinated only in spring attributed to the very dry weather in the experimental field during the study time period. Both cohorts completed their life cycle in early summer, plants from seeds germinated in autumn behaved as winter annuals while plants from seeds germinated in spring behaved as early spring ephemerals. Whether watered or not, whether germinated in autumn or in spring, germination percentages of group1 were the lowest but the fitness of seedlings and plants from them were the highest, while germination percentages of group3 were the highest but the fitness of seedlings and plants from them were the lowest. For a seed group, germination percentages, seedling survival, plant size, number of seeds per plant and total number of seeds from all surviving plants in autumn were higher than that in spring.Seeds of three groups were different in life history strategies, and seed position–dependent mass was highly associated with characteristics in life history. These characteristics indicated a kind of"bet-hedghing"strategies, which was good to successful establishment and population expansion of species in Jungger desert with highly temporal and spatial heterogeneity.