Effect Of Storage Condition And Temperature On Seed Dormancy And Germination Of Species From An Alpine Meadow On Eastern Tibet Plateau

Dormancy and germination are central seed traits related to the regeneration niche of a species, and they can affect the distribution and abundance of species in communities. Much research has been done on seed dormancy and germination; however, most of this work was done at the species level; few studies were done at the community level. Thus, little is known about the effect of environmental conditions on seed dormancy break and germination at the community level or how climate change might affect these seed traits. The temperature requirement for seed dormancy breaking and germination is an important aspect of the germination niche, and it can affect seed germination time and the geographic distribution of species. Germination response to fluctuating temperatures is a mechanism by which seeds detect gaps in vegetation canopies and depth of burial in soil, and it is very important for recruitment of plants following habitat disturbance. Understanding these aspects of seed ecology at the community level will help us predict the effect of climate change on plant community structure. We investigated the germination ecology of 973 species, 355genera and 66families from high elevation grasslands on the eastern Tibet Plateau at the community level.The key results 1) Based on the germinability of seeds of the same species stored under different conditions, germination may increase, decrease, or stay the same.2) Compared to wet cold conditions, storing seeds at dry warm or at dry cold conditions decreased the mean community germination percentage by 17.93% and 16.07%, respectively; storing seeds at dry warm vs. dry cold conditions decreased the community mean germination percentage by 4.61%.3) The germination response to moisture conditions during storage showed significant phylogenetic patterns, whereas the germination response to storage temperature did not.4) Taking all species into account, alternating temperatures increased germination percentages regardless of temperature amplitude; however, germination rate (speed) was decreased by the 5/25℃regime.5) Based on habitat, the proportion of species that responded positively to temperature fluctuation could be arranged as follows:disturbed grounds>forest margins /crubs> marshlands> alpine/subalpine meadows>dry sunny slopes.6) Species distributed only at high elevations (>2000m) did not show a significant germination response to temperature fluctuation, whereas those occurring at both high and low elevations had a significant positive response.7) Germination of annuals was significantly promoted by 5/25℃but not by 10/20℃, whereas germination of perennials was significantly promoted by both 5/2℃and 10/20℃.8) Small-seeded species were more likely than large-seeded ones to respond positively to fluctuating temperatures.9) Annuals/biennials and perennials have different optimal temperatures for seed germination.10) Species from marshlands have a higher optimal temperature for germination than those living in other habitats.11) Species with different altitudinal distributions and those with different seed masses have different responses to low temperature.12) Dominant species (Cyperaceae) have different optimum germination temperature and a different response to low temperature than common species (Poaceae and Asteraceae).Conclusions Within the high-elevation Tibetan grassland community, seeds of species stored at the same conditions showed differences in dormancy breaking and germination responses. These differences may have implications for understanding how this community might respond to climate change. Fluctuating temperatures improved germination at the community level, and the germination response to temperature fluctuation was affected by seed mass, life cycle type, habitat and altitudinal distribution. Thus, groups of species that are distinguished by different seed masses, life cycle types, habitats or altitudinal distributions usually have a different optimum germination temperature and different response to low temperature. These differences in the germination niche help promote and maintain biodiversity.