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Abstract: Very few studies have examined whether the impacts of grazing disturbance on soil seed banks occur directly or indirectly through aboveground vegetation and soil properties. The potential role of the seed bank in alpine wetland restoration is also unknown. We used SEM (structural equation modeling) to explore the direct effect of grazing disturbance on the seed bank and the indirect effect through aboveground vegetation and soil properties. We also studied the role of the seed bank on the restoration potential in wetlands with various grazing intensities: low (fenced, winter grazed only), medium (seasonally grazed), and high (whole‐year grazed). For the seed bank, species richness and density per plot showed no difference among grazing intensities for each depth (0–5, 5–10, 10–15 cm) and for the whole depth (0–15 cm) in spring and summer. There was no direct effect of grazing disturbance on seed bank richness and density both in spring and summer, and also no indirect effect on the seed bank through its direct effect on vegetation richness and abundance. Grazing disturbance indirectly increased spring seed bank density but decreased summer seed bank density through its direct effect (negative correlation) on soil moisture and total nitrogen and its indirect effect on vegetation abundance. Species composition of the vegetation changed with grazing regime, but that of the seed bank did not. An increased trend of similarity between the seed bank and aboveground vegetation with increased grazing disturbance was found in the shallow depth and in the whole depth only in spring. Although there was almost no change in seed bank size with grazing intensities, grazing disturbance increased the quantity of transient seeds but decreased persistent seeds. Persistent seeds stored in the soil could play a crucial role in vegetation regeneration and in restoration of degraded wetland ecosystems. The seed bank should be an integral part of alpine wetland restoration programs. [ABSTRACT FROM AUTHOR]

Interspecific variation in seed mass and the degree of seed dormancy can contribute to the differentiation in the regeneration niche of co-occurring plant species. At the community level, however, little is known about the combined effects of biotic (seed mass) and abiotic (light availability) competitive factors on the germination proportion (GP) across species. We determined the GP for 613 angiosperm species of the eastern Qinghai-Tibet plateau grasslands under two light treatments in the field: high-light (i.e., natural) and low-light. We also measured the change in germination proportion (CGP) across both treatments for all species. Furthermore, we used both standard linear models and phylogenetic generalized linear models to test whether or not GP and CGP were associated with seed mass, which is an important trait for competitive interactions. We found a significant negative relationship between GP and seed mass only in the high-light treatment; that is, smaller seeds had a greater potential for germination than did large seeds, though this was absent under low-light. Additionally, we found a significant positive correlation between CGP and seed mass; that is, smaller-seeded species (those with a high GP under high-light) tended to germinate less whereas the larger-seeded species (low GP under low-light) tended to germinate more under low-light vs. high-light conditions. We also found that closely related species shared a similar GP in both light environments, and that they also had similar values for CGP and seed mass. In sum, a low light availability appears to neutralize the negative effect of greater seed mass on GP, thus possibly reducing the degree of regeneration niche differentiation among small- and large-seeded species. This field study has important implications for better understanding the effects of light availability on species’ regeneration niche differentiation at the community level, and for interpreting how plant communities are assembled from traits of seed—the starting point of the plant life cycle. [ABSTRACT FROM AUTHOR]

Germination timing is a key transition of life history. It not only links subsequent life-history traits, such as plant height and flowering time, but also provides a link to the previous generation through the influence of the maternal environment. Environmental factors may mediate these key links, and consequences of this process may influence species regeneration and dispersal. However, little is known about how environmental factors mediate these key links. Here, germination timing under high (natural light) and low light treatments was estimated for 476 angiosperm species of the eastern Tibetan Plateau grasslands. Furthermore, we used standard (std) and phylogenetic (phy) comparative methods to test if germination timing was associated with plant height, flowering time and maternal habitats under both light treatments. Germination timing was positively correlated with plant height only in low light in std-methods. Germination timing was associated with onset of flowering in both light treatments in std-methods, but only in low light when using phy-methods. Germination timing was positively correlated with elevation only in low light when using both comparative methods. Germination timing was correlated with water in maternal habitat only in high light when using both comparative methods. Germination timing was associated with light in maternal habitat in both light treatments in std-methods, but only in high light when using phy-methods. In summary, light-dependent associations of germination timing with subsequent life-history traits and maternal habitats may influence the probability of plant species life-cycle completion and influence distribution and dispersal of plant species in natural plant communities. [ABSTRACT FROM PUBLISHER]

Background: Although the effect of water level on germination in soil seed banks has been documented in many ecosystems, the mechanism is not fully understood, and to date no empirical studies on this subject exist. Further, no work has been done on the effect of water level on seed banks of drying and saline-alkaline wetlands in alpine areas on the Tibetan Plateau. Methodology: We examined the effects of water level (0 cm, 5 cm and 10 cm) on seed germination and seedling establishment from soil seed banks at 0–5 cm and 5–10 cm depths in typical, drying, and saline-alkaline wetlands. We also explore the potential role of soil seed bank in restoration of drying and saline-alkaline wetlands. Principal Findings: Species richness decreased with increase in water level, but there almost no change in seed density. A huge difference exists in species composition of the seed bank among different water levels in all three wetlands, especially between 0 cm and 5 cm and 0 cm and 10 cm. Similarity of species composition between seed bank and plant community was higher in 0 cm water level in drying wetland than in the other two wetlands. The similarity was much higher in 0 cm water level than in 5 cm and 10 cm water levels in all three wetlands. Species composition of the alpine wetland plant community changed significantly after drying and salinization, however, species composition of the seed bank was unchanged regardless of the environment change. Conclusions/Significance: Water level greatly affects seed bank recruitment and plant community establishment. Further, different water levels in restored habitats are likely to determine its species composition of the plant community. The seed bank is important in restoration of degraded wetlands. Successful restoration of drying and salinization wetlands could depend on the seed bank. [ABSTRACT FROM AUTHOR]

Abstract: The primary goal was to address a question with regard to whether the seed bank be regarded as a potential as a source of seeds for saline–alkaline meadow restoration on the Tibetan Plateau. We collected soil samples, soil seed bank samples, sampled the vegetation in a seasonal wetland and in a saline–alkaline meadow, and used the NMDS (nonmetric multidimensional scaling) to evaluate the relationship of species composition between the seed banks and vegetation. The saline–alkaline meadow develops after drying of wetlands following disturbance. Soil properties, and seed density and species richness were compared. The seed density and species richness of the seed banks showed no difference between the two habitats. The NMDS results showed that composition of the vegetation of the two sites was obviously different, but that of the seed bank was not. The drying of the wetland altered plant community and soil properties. Persistent seed bank can be regarded a strategy of adaptation to current soil environment (high soil moisture or salinity). There was a significant negative effect on soil characteristics after wetland drying and subsequent salinization. If hydrology is restored, the seed bank will continue to be an importance source of diversity of propagules for saline–alkaline meadow restoration following disturbance. [Copyright &y& Elsevier]

Climate change is predicted to dramatically alter the composition of plant communities. The impact of climate change on these communities is often based on short-term warming experiments, which have revealed marked declines in species diversity in response to relatively minor increases in average annual temperatures. The long-term effects of such warming on community diversity and composition, however, are less well understood. Here, we formalize a hypothesis of rebounding diversity, where species richness initially declines in response to warming, but subsequently recovers through a combination of colonization (via dispersal and seed banks) and competitive release (via shifts in the dominant species). We compared long-term changes in species diversity and abundance between control and experimentally warmed (1–2 °C) plots, sampled over an 18-year period, in alpine meadow communities of the Qinghai-Tibet plateau. While there was an initial decline in species diversity by c. 40% (11–19 species) over the first four years, 18 years later, diversity had rebounded to initial levels, on a par with control plots. The composition of the experimentally warmed communities, however, was significantly altered. Our study suggests that short-term experiments may be insufficient to capture the temporal variability in community diversity and composition in response to climate change. Rather, the long-term impacts of continued global warming are predicted to result in highly dynamic processes of community reassembly and turnover that do not necessarily lead to a net decline in local diversity, but do lead to the formation of novel communities. [ABSTRACT FROM AUTHOR]

• We found two major dimensions of germination [early (fast) vs. late (slow); high vs. low]. • Taxa exhibited diverse germination strategies; related taxa exhibited similar germination strategies. • Low light availability altered the frequencies of germination strategies. • Local habitat conditions and life-history traits can influence germination strategies. Germination strategies vary widely among species and significantly influence individual fitness and community diversity. Germination strategies are known to be influenced by environmental conditions, life-history traits and evolutionary history, but how these factors influence germination across species under natural conditions is poorly understood. Here, we characterized germination strategies of 789 angiosperm species from the eastern Tibetan Plateau based on germination time courses and the final germination proportion expressed in the field under three light treatments: high (i.e., natural) light, medium light and low light. Based on results of correlation analysis and cluster analysis, we found two major dimensions of germination strategies [early (fast) versus late (slow) germination and high versus low germination proportions]. We also characterized a "dormant" germination strategy (species with final germination proportion < 5%). Low light availability altered the frequencies of germination strategies, and tended to canalize germination strategy into the extreme categories of early germination or high levels of dormancy. Germination strategy varied significantly based on species life-history traits (seed mass and adult longevity) and local habitat conditions (elevation, water habitat and light habitat). Finally, germination strategy exhibited strong phylogenetic signal, such that related taxa exhibited similar germination strategies. In sum, the diversity of germination strategies we observed among these species is maintained by a combination of local habitat conditions, evolutionary history and the correlated selection acting on germination and key life-history traits. [ABSTRACT FROM AUTHOR]