| As the most widely research field in plant ecology, seed germination is always a hot topic to be discussed. Variation in seed germination behavior is a functional response of a plant to the predictability of its abiotic and biotic environment. The timing and level of germination strongly affect a plant’s recruitment success and may consequently have implications for species distribution. It is also thought to play an important role in promoting species coexistence within communities. As the most critical stage in the life history, germination plays a role in connecting. On one hand, seed carries the genetic materials from the parents and has a deep imprint of the mother habitat; On the other hand, seed also links the growth and development stage after germination.In recent years, researchers have been carried out a lot of work on seed germination patterns, however, relatively few studies investigate seed germination in alpine meadow on the Tibetan Plateau and there are still some important problems that remain to be resolved:Firstly, to alpine plants, which are expected to be affected more by climate warming, the effects of temperature on germination have hardly been known from a community perspective. Secondly, germination behavior is the combined results of multiple factors, many studies measured the effects of one variable at a time, ignoring the possibility that correlations among several life history or ecological variables. Thirdly, to explore the relationship between germination behavior and species distribution can be very useful for predicting the community dynamics, yet such research is rare in alpine region. Based on the frontier of plant ecology, combining theoretical analysis and experimental investigations, we chose202common species from an alpine meadow on the eastern Tibetan Plateau, set five temperature treatments according to the natural temperature change tendency, used GLM model and phylogenetic method and examined the effects of phylogenetic, life history attributes on seed germination and its response to environmental changes, in order to investigate the germination behavior of the alpine species deeply, and provide theoretical basis for plant protection and community maintainance in Tibetan Plateau. The main results and conclusions are as follows:(1) In the alpine meadow on the Tibetan Plateau, mean germination percentage (GP) and mean germination time (GT) differed significantly among phylogenetic taxa (order and family), and order could explain7.6%of the variance in mean GT independently. GP, GT and the plasticity of germination behavior under different temperature treatments were phylogenetically conserved traits, indicating that the germination behavior of this community was strongly constrained by phylogeny.(2) Germination characteristics were affected significantly by life history attributes, such as life history cycle, seed size, dispersal mode, dispersal time and flowering time, but the contribution of these factors were relatively small in the variance of GT. In details, life history cycle, seed size and dispersal mode could explain0.8%,1.0%and0.9%of the variance in mean GT independently, respectively; there were significant interactions between phylogeny and life history attributes, after correcting the effects of phylogeny, the effects of life history cycle, seed size and dispersal mode on germination were still significantly.(3) In the alpine meadow on the Tibetan Plateau, temperature was the most important factor in regulating germination time, which could explain12.8%of the variance in GT; the results demonstrated that elevated temperature would lead to a significant increase in germination percentage and an accelerated germination, but germination behavior in response to temperature changes varied interspecifically. Mean GP at5/25℃,10/20℃,10/25℃treatment was5.89%,2.29%, and2.37%higher than5/20℃, respectively; Mean GT at5/25℃,10/20℃,10/25℃treatment was0.56days,2.39days and2.11days lower than5/20℃, respectively.(4) There was no significant interaction between temperature and other factors in determining GT variation. GT in response to temperature change was independent of other life history attributes, indicating that in germination process, the regulation of temperature on germination behavior was relatively independent.(5) Moreover, there was a significant increase in seed mortality due to fungal attack because of temperature rise. We inferred that high seed mortality was likely to produce selection pressures on germination, which could be one reason of good germination under a relatively high temperature environment.(6) On the family level, the variation of germination of Asteraceae and Poaceae was lowest, the species of these two families displayed stable germination strategy, suggesting in the regeneration process, they had already got the competitive advantage, which could be one of the main reason why Asteraceae and Poaceae species occupy a dominant position in alpine meadow community.(7) As the reflection of the maternal effects, germination behavior was significantly affected by habitat, which could explain3.9%of the GT variation independently. On one hand, mean GP of seeds from south slope was2.28%,10.62%and16.99%higher than those from north slope, shrub and bottomland, respectively. On the other hand, mean GT of seeds from south slope was0.80days,4.94days and3.94days lower than those from north slope, shrub and bottomland, respectively. Moreover, there were strong interactions between life history attributes (such as life history cycle, seed size, dispersal mode) and habitat, suggesting habitat could act germination process through these factors.(8) Storage time significantly affected germination behavior, the majority of species reduced GP significantly after storage more than seven years, but the impact of short-term storage (1-5years) on the germination behavior had interspecific differences.(9) The effect of altitude on GT was not statistically significant, GT of widespread species (species distributed both≥and<2000m) and species distributed only≥2000m were13.26days and13.39days respectively. However, GP of seeds differed between altitudinal distribution groups, and widespread species displayed relatively lower mean GP (40.62%) than species distributed only≥2000m (45.16%), thus our results did not support the point that there were positive correlation between species distribution and germination niche.(10) There were significant interactions between phylogenetic group and environmental attributes, between phylogenetic group and life history attributes, and between life history attributes and environmental factors in determining germination patterns. It can be inferred that germination behavior does not evolve independently of each other but from part of an adapted syndrome of life history traits. |
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