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In restoration ecology, the transition from desired to degraded state is based solely on the composition of the aboveground plant community, whereas belowground propagules are often neglected. We developed a conceptual framework integrating seed bank dynamics into alternative stable state theory, highlighting the important relationship between aboveground and belowground composition. This integration emphasizes the role of resilience in systems that appear to have shifted to an "undesirable" state. Belowground propagules, especially soil seed and bud banks, provide buffering capacity and may serve as valuable indicators of potential resistance to state transition based on the degree of similarity between belowground and aboveground vegetation composition. Ecosystem states may have multiple components that differ in their rate of change, as well as in their capacity to promote resilience. We recommend that the application of alternative stable state theory from a management perspective should incorporate components of both above- and belowground vegetation. [ABSTRACT FROM AUTHOR]

Background and aims: Soil seed banks are an important source of seedling recruits in grassland ecosystems, particularly following large-scale disturbance. Nonetheless, the relative importance of above-ground plant communities versus below-ground processes in maintaining these seed banks is poorly understood. Methods: Here we collected 1026 soil seed bank samples and sampled 171 aboveground vegetation quadrats in 57 sites representing six distinct grass-dominated vegetation types present at high elevation on the Tibetan Plateau, China. To understand processes affecting seed banks at these sites we examined the associations of soil environmental variables with community composition, density and species richness. Results: We found significant differences in species composition between the seed bank and standing vegetation in each of the vegetation types, whereas soil seed banks were much more similar to each other. Nonetheless, seed bank composition was significantly associated with soil moisture, pH, and available nitrogen (all p < 0.05). Seed density was significantly negatively correlated with soil pH and positively correlated with soil moisture and soil organic matter. Multiple regression analysis showed that for seed bank density a model including pH alone had the lowest AIC value. Conclusions: Soil conditions influence not only seed inputs but also potentially seed survival in the soil, this study present a framework which supply a plausible explanation on effect of soil environment factors (chemical and physical factors) in the formation of species composition of soil seed bank. Future work should isolate the direct and indirect effects of soil chemistry on seed persistence using seed burial experiments. [ABSTRACT FROM AUTHOR]

High altitude wetlands on the Tibetan Plateau have been shrinking due to anthropogenic disturbances and global climate change. However, the few studies that have been conducted on wetlands are inconclusive about the effect of soil moisture on seed banks and potential of seed banks in wetlands with different levels of soil moisture for regeneration of dried wetlands. We investigated seed banks and plant communities along a soil moisture gradient. A structural equation model was used to analyze the direct and indirect effects of soil moisture on seed banks, as well as the relationship between plant communities and seed banks. Although soil moisture had no direct effects on seed bank richness and density and indirect effects on seed banks through plant community, it had indirect effects on the seed bank through soil pH. Soil moisture also did not have direct effects on plant community richness, but it had indirect effects through soil pH. Plant community composition changed with soil moisture, but aboveground plant abundance and seed banks composition did not change. Low similarity exists between plant community and seed banks for all wetlands, and similarity decreased along the moisture gradient. The key factor determining plant community diversity was soil pH, while seed bank diversity was mainly affected by soil pH and plant community diversity with wetland drying. Although potential for regenerating the plant community from the seed bank decreased with an increase in soil moisture, drained wetlands still have enough residual seeds for successful restoration of species-rich alpine meadows. [ABSTRACT FROM AUTHOR]

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]

Background: Knowledge about how change the importance of soil seed bank and relationship between seed mass and abundance during vegetation succession is crucial for understanding vegetation dynamics. Many studies have been conducted, but their ecological mechanisms of community assembly are not fully understood. Methodology: We examined the seasonal dynamics of the vegetation and soil seed bank as well as seed size distribution along a successional gradient. We also explored the potential role of the soil seed bank in plant community regeneration, the relationship between seed mass and species abundance, and the relative importance of deterministic and stochastic processes along a successional gradient. Principal Findings: Species richness of seed bank increased (shallow layer and the total) and seed density decreased (each layer and the total) significantly with succession. Species richness and seed density differed significantly between different seasons and among soil depths. Seed mass showed a significant negative relationship with relative abundance in the earliest successional stage, but the relationships were not significant in later stages. Seed mass showed no relationship with relative abundance in the whole successional series in seed bank. Results were similar for both July 2005 and April 2006. Conclusions: The seed mass and abundance relationship was determined by a complex interaction between small and larger seeded species and environmental factors. Both stochastic processes and deterministic processes were important determinants of the structure of the earliest stage. The importance of seed bank decreased with succession. The restoration of abandoned farmed and grazed meadows to the species-rich subalpine meadow in Tibetan Plateau can be successfully achieved from the soil seed bank. However, at least 20 years are required to fully restore an abandoned agricultural meadow to a natural mature subalpine meadow. [ABSTRACT FROM AUTHOR]

Background and Aims: Information on soil seed bank processes is crucial for understanding vegetation dynamics. Despite the documented importance of soil seed banks in many ecosystems, their role is not fully understood in some sensitive habitats, such as the alpine meadows of the Tibetan Plateau. Methods: We studied the seasonal dynamics of the germinable soil seed bank under four disturbance intensities in an alpine meadow on the Tibetan Plateau as well as seed size distribution relative to disturbance intensity. Composition of the seed bank was compared with that of the standing vegetation. Results: Density of buried seeds increased with disturbance intensity, but species richness and species diversity decreased. Seed density and species richness of the seed bank varied seasonally in all layers (0-2, 2-7, 7-12 cm) and the whole (0-12 cm). The species composition of seed bank was not significantly influenced by season. There was no trend in seed size distribution as disturbance increased. Seasonal seed bank turnover rates increased with increase in disturbance. The result of the NMDS showed that species composition of seed bank and vegetation exhibited a fairly uniform pattern in each season. Conclusions: Although as a whole the species composition of the vegetation and seed bank showed a relatively low degree of similarity in each season, similarity was highest in the most disturbed habitat. There was no alteration in species composition of seed bank regardless of disturbance intensity, but seed density decreased as disturbance increased. Disturbances in alpine plant communities might increase persistence of regeneration niches. Regeneration from the seed bank together with vegetative reproduction contributed to aboveground vegetation in highly disturbed habitats. Clonal species played an important role in regeneration of vegetation in slightly disturbed areas, where there was little contribution of ruderals from soil seed banks. [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]

Abstract: We examined the role of the soil seed bank along a grazing disturbance gradient and its relationship with the vegetation of alpine meadows on the Tibet plateau, and discussed the implications for restoration. The seed bank had a high potential for restoration of species-rich vegetation; 62 species were identified in the vegetation and 87 in the seed bank, 39 species being common to both. Mean seed density was 3069–6105 viable seeds m−2. The density of buried seeds increased significantly with increasing disturbance, indicating that restoration of disturbed areas is not seed limited. Seed density and species richness decreased with depth. The proportion of perennial species decreased with decrease in disturbance both in seed bank and in vegetation. A large portion of species with persistent seeds in the disturbed areas indicate that this seed type can be regarded a strategy of adaptation to current disturbances. Detrended correspondence analysis (DCA) showed significant differences of species composition between seed bank and vegetation, except for the seriously disturbed site. Our results suggest that the establishment of new species in severely disturbed areas is more dependent on the seed bank. By contrast, the restoration in less-disturbed and mature meadows does not rely on seed banks, and the establishment of the vegetation in these communities is more likely to rely on seed dispersal from the standing vegetation and on species with vegetative reproduction. [Copyright &y& Elsevier]

The soil seed bank represents valuable rebuilding capital that may rescue an ecosystem from state transition once vegetation has crossed an apparent threshold from the desired to degraded state. However, almost no research has explored the response of transient and persistent seed banks and their role in plant community regeneration along a gradient of wetlands from intact to a seriously degraded state due to increased grazing disturbance.Seven grazing disturbance levels from nondisturbed to highly degraded alpine marsh ecosystems were selected on the eastern Tibetan Plateau. Akaike information criterion (AIC) was used to select the best‐fit model to predict the response of the plant community, soil seed bank and Bray–Curtis dissimilarity index to increased grazing disturbance.Both the plant community and seed bank showed a nonlinear change with increasing grazing disturbance. Species richness and seed density of the transient seed bank first decreased and then increased with increased disturbance, but the persistent seed bank showed a reverse trend, with an obvious threshold. Species composition of the persistent and transient seed banks exhibited little change compared to the plant community as disturbance increased. Similarities between both the persistent and transient seed banks and plant community also showed a nonlinear change with increased disturbance, while the persistent seed bank had a higher similarity with the plant community than the transient seed bank.Synthesis: At high grazing disturbance, persistent seed banks are more important than transient seed banks in plant community regeneration. Alpine wetland ecosystems have intrinsic resilience because the persistent seed bank has a pool of species above the threshold. However, ecosystem resilience declines if the species pool of the persistent seed bank is depleted below the threshold. The restoration potential of the seed bank has limits, and it will gradually be exhausted when species losses due to increased grazing intensity exceed the threshold of state transition. [ABSTRACT FROM AUTHOR]

Background: Cold hardiness is fundamental for amphibians to survive during the extremely cold winter on the Qinghai-Tibet plateau. Exploring the gene regulation mechanism of freezing-tolerant Rana kukunoris could help us to understand how the frogs survive in winter. Results: Transcriptome of liver and muscle of R. kukunoris collected in hibernation and spring were assisted by single molecule real-time (SMRT) sequencing technology. A total of 10,062 unigenes of R. kukunoris were obtained, and 9,924 coding sequences (CDS) were successfully annotated. Our examination of the mRNA response to whole body freezing and recover in the frogs revealed key genes concerning underlying antifreeze proteins and cryoprotectants (glucose and urea). Functional pathway analyses revealed differential regulated pathways of ribosome, energy supply, and protein metabolism which displayed a freeze-induced response and damage recover. Genes related to energy supply in the muscle of winter frogs were up-regulated compared with the muscle of spring frogs. The liver of hibernating frogs maintained modest levels of protein synthesis in the winter. In contrast, the liver underwent intensive high levels of protein synthesis and lipid catabolism to produce substantial quantity of fresh proteins and energy in spring. Differences between hibernation and spring were smaller than that between tissues, yet the physiological traits of hibernation were nevertheless passed down to active state in spring. Conclusions: Based on our comparative transcriptomic analyses, we revealed the likely adaptive mechanisms of R. kukunoris. Ultimately, our study expands genetic resources for the freezing-tolerant frogs. [ABSTRACT FROM AUTHOR]

The ongoing climate change on the Tibetan Plateau, leading to warming and precipitation anomalies, modifies phosphorus (P) cycling in alpine meadow soils. However, the interactions and cascading effects of warming and precipitation changes on the key "extracellular" and "intracellular" P cycling genes (PCGs) of bacteria are largely unknown for these P‐limited ecosystems. We used metagenomics to analyze the individual and combined effects of warming and altered precipitation on soil PCGs and P transformation in a manipulation experiment. Warming and increased precipitation raised Olsen‐P (bioavailable P, AP) by 13% and 20%, respectively, mainly caused by augmented hydrolysis of organic P compounds (NaOH‐Po). The decreased precipitation reduced soil AP by 5.3%. The richness and abundance of the PCGs' community in soils on the cold Tibetan plateau were more sensitive to warming than altered precipitation. The abundance of PCGs and P cycling processes decreased under the influence of individual climate change factors (i.e., warming and altered precipitation alone), except for the warming combined with increased precipitation. Pyruvate metabolism, phosphotransferase system, oxidative phosphorylation, and purine metabolism (all "intracellular" PCG) were closely correlated with P pools under climate change conditions. Specifically, warming recruited bacteria with the phoD and phoX genes, which encode enzymes responsible for phosphoester hydrolysis (extracellular P cycling), strongly accelerated organic P mineralization and so, directly impacted P bioavailability in alpine soil. The interactions between warming and altered precipitation profoundly influenced the PCGs' community and facilitated microbial adaptation to these environmental changes. Warming combined with increased precipitation compensated for the detrimental impacts of the individual climate change factors on PCGs. In conclusion, warming combined with rising precipitation has boosting effect on most P‐related functions, leading to the acceleration of P cycling within microbial cells and extracellularly, including mineralization and more available P release for microorganisms and plants in alpine soils. [ABSTRACT FROM AUTHOR]

Low available soil nitrogen (N) limits plant productivity in alpine regions, and alpine plants thus resorb and reallocate N from senescing tissues to conserve this limited N during the non‐growing season. However, the destination and extent of N redistribution during plant senescence among above‐ and below‐ground organs, let alone other processes of translocation outside of plants and into the soil components, remain poorly understood.Utilizing 15N stable isotope as a tracer, we quantified N redistribution among above‐ and below‐ground plant organs and different soil components during senescence in an alpine meadow ecosystem, and explored the relationship between 15N partitioning among plant–soil N pools with seasonal fluctuations of plant functional traits.We found a substantial depletion of 15N in fine roots (−40% ± 2.8%) and above‐ground tissues (−51% ± 5.1%), and an enhanced 15N retention primarily in coarse roots (+79% ± 27%) and soil organic matter (+37% ± 10%) during plant senescence, indicating a dual role of roots with coarse roots acting as an N sink and fine roots as a source of N recycling during senescence. In parallel, we observed a temporal variation in plant functional traits, representing a shift from more acquisitive to more conservative strategies as the growing season ends, such as higher coarse root N and coarse root to fine root ratio. The seasonal trait variations were highly correlated with the 15N retention in coarse roots and soil organic matter. Particularly, 15N retention in particulate and mineral‐associated organic matter increased by 30% ± 12% and 24% ± 9%, respectively, suggesting a potential pathway through which fine root and microbial mortality contribute to 15N redistribution into soil N pools during senescence.Synthesis. N redistribution and seasonal plant trait fluctuation facilitate plant N conservation and ecosystem N retention in the alpine system. This study suggests a coupled above‐ground‐below‐ground N conservation strategy that may optimize the temporal coupling between plant N demand and ecosystem N supply in N‐limited alpine ecosystems. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau has undergone significant climate warming in recent decades, and precipitation has also become increasingly variable. Much research has explored the effects of climate change on vegetation on this plateau. As potential vegetation buried in the soil, the soil seed bank is an important resource for ecosystem restoration and resilience. However, almost no studies have explored the effects of climate change on seed banks and the mechanisms of these effects. We used an altitudinal gradient to represent a decrease in temperature and collected soil seed bank samples from 27 alpine meadows (3,158–4,002 m) along this gradient. A structural equation model was used to explore the direct effects of mean annual precipitation (MAP) and mean annual temperature (MAT) on the soil seed bank and their indirect effects through aboveground vegetation and soil environmental factors. The species richness and abundance of the aboveground vegetation varied little along the altitudinal gradient, while the species richness and density of the seed bank decreased. The similarity between the seed bank and aboveground vegetation decreased with altitude; specifically, it decreased with MAP but was not related to MAT. The increase in MAP with increasing altitude directly decreased the species richness and density of the seed bank, while the increase in MAP and decrease in MAT with increasing altitude indirectly increased and decreased the species richness of the seed bank, respectively, by directly increasing and decreasing the species richness of the plant community. The size of the soil seed bank declined with increasing altitude. Increases in precipitation directly decreased the species richness and density and indirectly decreased the species richness of the seed bank with increasing elevation. The role of the seed bank in aboveground plant community regeneration decreases with increasing altitude, and this process is controlled by precipitation but not temperature. [ABSTRACT FROM AUTHOR]

Flowering and fruiting phenology of plants is sensitive to environmental cues, and changes in reproductive phenology of individual plant species under climate change have been widely reported. However, how species‐level phenological responses scale up to affect community‐level reproductive phenology patterns (synchrony and reproductive duration) are still unclear.An experiment on the effects of nitrogen (N) addition and precipitation changes on reproductive phenological traits of 52 species was conducted in an alpine meadow on the eastern Tibetan Plateau to determine the influence of the phenological response in different functional groups on community‐level reproductive phenology.N addition significantly delayed the onset date of reproductive phenology of sedges (early‐flowering species) and advanced the end date of reproduction of forbs (late‐flowering species). Meanwhile, N addition reduced the number of individuals involved in reproduction of sedges and forbs, but it increased that of grasses (late‐flowering species). Furthermore, N addition increased reproductive synchrony, delayed the onset and shortened the duration of reproductive phenology at the community level. However, precipitation changes and their interaction with N addition had no significant effect on reproductive phenology of the alpine plant community.Synthesis. These results suggested that differences in the direction and magnitude of response of different species to N enrichment lead to compression of reproductive duration at the community level, increasing the degree of overlap between reproductive events, which could change future species diversity, trophic interactions and productivity accumulation in alpine meadows on the Tibetan Plateau. Overall, knowledge of phenological responses from plant functional groups to the community level contributes to robust prediction and mechanistic understanding of community structure and function in response to future climate change. [ABSTRACT FROM AUTHOR]

Summary: Nitrogen (N) enrichment is widely known to affect the root‐associated arbuscular mycorrhizal fungal (AMF) community in different ways, for example, via altering soil properties and/or shifting host plant functional structure. However, empirical knowledge of their relative importance is still lacking.Using a long‐term N addition experiment, we measured the AMF community taxonomic and phylogenetic diversity at the single plant species (roots of 15 plant species) and plant community (mixed roots) levels. We also measured four functional traits of 35 common plant species along the N addition gradient.We found divergent responses of AMF diversity to N addition for host plants with different innate heights (i.e. plant natural height under unfertilized treatment). Furthermore, our data showed that species‐specific responses of AMF diversity to N addition were negatively related to the change in maximum plant height. When scaling up to the community level, N addition affected AMF diversity mainly through increasing the maximum plant height, rather than altering soil properties.Our results highlight the importance of plant height in driving AMF community dynamics under N enrichment at both species and community levels, thus providing important implications for understanding the response of AMF diversity to anthropogenic N deposition. [ABSTRACT FROM AUTHOR]

Asymmetrical light competition and direct detrimental effect of nitrogen have been proposed as two main mechanisms driving species richness declines following nitrogen (N) addition. N addition is also known to alter functional trait composition towards increased dominance of tall and fast‐growing species. However, whether trait changes vary between species and, in particular, how the traits of tall and short species respond to N addition has rarely been studied. Understanding whether different trait changes occur for tall and short species would provide insight into mechanisms underlying N addition effects.Based on a long‐term N addition experiment, we measured the natural height of 44 plant species and the photosynthetic active radiation (PAR) at seven heights in the vegetation and identified a clear stratification of the plant community into tall species (>30 cm tall), which experienced high light conditions, and short species that grew under the canopy. We also measured four functional traits, including maximum plant height, specific leaf area, leaf dry matter content and leaf thickness, on 35 species that occurred in fertilized and unfertilized plots.Structural equation modelling revealed that nitrogen (N) addition significantly reduced species richness by enhancing light asymmetry and had no direct effects, suggesting that N detrimental effects are negligible in our system. Consistent with this, we found different responses of traits and diversity for the tall and short species. Specifically, N addition reduced the number of short species but increased the number of tall species. In addition, specific leaf area increased, and leaf dry matter content decreased, for short species only, suggesting that they shifted to a fast growth strategy to cope with lower light levels. In contrast, tall species increased their height further to capture more light at the top of the canopy.Synthesis. The divergent trait responses observed for tall and short species show that although certain traits, like height and leaf traits, show correlated responses at the whole community level, these correlations may not be consistent across all species. Together, our results highlight that light competition is the main mechanism driving species loss following N addition. [ABSTRACT FROM AUTHOR]

The timing of phenological events is highly sensitive to climate change, and may influence ecosystem structure and function. Although changes in flowering phenology among species under climate change have been reported widely, how species‐specific shifts will affect phenological synchrony and community‐level phenology patterns remains unclear. We conducted a manipulative experiment of warming and precipitation addition and reduction to explore how climate change affected flowering phenology at the species and community levels in an alpine meadow on the eastern Tibetan Plateau. We found that warming advanced the first and last flowering times differently and with no consistent shifts in flowering duration among species, resulting in the entire flowering period of species emerging earlier in the growing season. Early‐flowering species were more sensitive to warming than mid‐ and late‐flowering species, thereby reducing flowering synchrony among species and extending the community‐level flowering season. However, precipitation and its interactions with warming had no significant effects on flowering phenology. Our results suggest that temperature regulates flowering phenology from the species to community levels in this alpine meadow community, yet how species shifted their flowering timing and duration in response to warming varied. This species‐level divergence may reshape flowering phenology in this alpine plant community. Decreasing flowering synchrony among species and the extension of community‐level flowering seasons under warming may alter future trophic interactions, with cascading consequences to community and ecosystem function. [ABSTRACT FROM AUTHOR]

Simple Summary: Both the warming climate and ultraviolet-B radiation are notable environmental factors affecting tadpole development. However, the phenotypes of tadpoles living at high altitudes may be improved by moderately warming temperatures, reducing or eliminating the negative effects of oxidative damage caused by cool temperatures or strong ultraviolet-B radiation. To verify this hypothesis, Rana kukunoris tadpoles, which live at high altitudes, were exposed to ultraviolet-B radiation and ultraviolet-B radiation-free environments at 14 (cool temperature) and 22 °C (warm temperature), respectively. Ultraviolet-B radiation and a warm temperature had opposite influences on several traits of the tadpoles, and the moderate temperature could compensate for or override the negative effects of ultraviolet-B radiation by increasing the tadpoles' preferred body temperature and critical tolerance temperature, thus enhancing the locomotion ability and thermal sensitivity of their antioxidant systems. The dark skin coloration and aggregation behavior of R. kukunoris tadpoles may also be effective strategies for allowing them to resist ultraviolet-B radiation and helping them to better adapt to a warming environment with stronger ultraviolet-B radiation. Thus, a moderate degree of warming may increase the capacity of living organisms to adapt to environmental changes and thus have positive effects on the development of tadpoles living at high altitudes. Both the warming climate and ultraviolet-B radiation (UVBR) are considered to be notable environmental factors affecting amphibian population decline, with particular effects on tadpole development. However, the phenotypes of tadpoles living at high altitudes may be improved by moderately warming temperatures, reducing or eliminating the negative effects of oxidative damage caused by cool temperatures or strong UVBR at high altitudes. To verify this hypothesis, Rana kukunoris tadpoles, which live at high altitudes, were used to test the effect of the interaction of temperature and UVBR on their development and antioxidant systems in a fully factorial design. The tadpoles were exposed to UVBR and UVBR-free environments at 14 (cool temperature) and 22 °C (warm temperature), respectively. UVBR and a warm temperature had opposite influences on several traits of the tadpoles, including their survival, developmental rate, individual size, preferred body temperature, thermal tolerance temperature, oxidative damage, and enzymatic and nonenzymatic antioxidant systems. The moderate temperature could compensate for or override the negative effects of UVBR by increasing the tadpoles' preferred body temperature and critical tolerance temperature, thus enhancing the locomotion ability and thermal sensitivity of their antioxidant systems. Furthermore, the dark skin coloration and aggregation behavior of R. kukunoris tadpoles may also be effective strategies for allowing them to resist UVBR and helping them to better adapt to a warming environment with stronger UVBR. Thus, it is possible that a moderate degree of warming may increase the capacity of living organisms to adapt to environmental changes and thus have positive effects on the development of tadpoles living at high altitudes. [ABSTRACT FROM AUTHOR]

Grazing by herbivores plays a key role in grassland ecosystems, but its effects on soil fauna biodiversity are not clear in alpine meadow ecosystems, especially on the Tibetan plateau. We investigated the effects of long-term grazing disturbance of varying intensities (low disturbed site, medially disturbed site, and seriously disturbed site) on ecosystem biodiversity and functional process using soil nematode communities. Soil physicochemical characteristics and plant communities were also measured to explore the relationships between soil nematode communities structure and key environment variable. Soil samples were collected in May, June, August, and October, 2013. The abundance of total nematode communities, plant feeders and bacterivores increased with the grazing intensity increase, and predators decreased with grazing intensity increase. Low disturbed site has the lowest abundance of fungivores. Grazing disturbance has no significant influence on abundance of omnivores ( P > 0.05). Species richness was highest on seriously disturbed site and lowest on low disturbed site. MI and SI decreased as grazing intensity increase. The highest NCR was found in low disturbed site and the lowest in medially disturbed site. The highest EI was found in medially disturbed site and the lowest in low disturbed site. Principal component analysis (PCA) showed that nematode communities could be separated by three different grazing disturbance intensity sites. Redundancy analysis (RDA) showed that Helicotylenchus , Acrobeloides and Labronema were positively correlated with higher plant communities diversity. Filenchus was positively correlated with forbs biomass. Some omnivores such as Eudorylaimus and Aporcelaimus was positively correlated with soil moisture and rich nutrient resources, meanwhile, Enchodelus and Coomansus was positively correlated with biomass of sedges and grasses. Anaplectus and Prismatolaimus significantly correlated with soil moisture, nutrient resources and biomass of sedges and grasses. This study revealed that grazing herbivores can change composition, structure and diversity of soil nematode communities, and then reflect radical shift in below-ground soil faunal biodiversity and processes in alpine meadow on the Tibetan plateau. [ABSTRACT FROM AUTHOR]

Nitrogen (N) inputs to terrestrial ecosystems are increasing faster than phosphorus (P) inputs, causing N:P imbalances and substantial changes in the diversity and structure of plant, soil microbial, and fauna communities. The responses of the soil micro-food web to N:P imbalances remain unclear but are crucial to understanding the impacts on ecosystem functioning. We investigated the effect of N and P additions on plant communities, edaphic properties, and nematode species diversity and composition, and assessed shifts in soil micro-food web complexity using nematode-based indices and structural equation modeling (SEM) in a nine-year nutrient addition experiment in an alpine meadow on the Tibetan Plateau. We found that N addition decreased the structure index (SI) and enrichment index (EI), indicating that N enrichment led to a simplification of the soil micro-food web. The addition of P alleviated the negative effect of N on soil micro-food web complexity but did not restore nematode community composition. The SEM supported the hypothesis that N addition simplified soil micro-food webs through increases in the N:P ratio and associated reductions in plant species richness, while P addition ameliorated the effect of N by decreasing the soil N:P ratio and increasing plant species richness. Our results highlight the positive effects of plant diversity in maintaining the complexity of the soil micro-food web. Our findings provide information that can be used to guide sustainable management and restoration of grasslands to alleviate the projected effects of future N:P imbalances on the soil micro-food web. However, efforts should be made to avoid nutrient deposition given the observed effects on both plant and nematode communities that could not be restored by alleviating the N:P imbalance through P addition. • Phosphorus alleviates soil micro-food web simplification caused by excess nitrogen. • Nematode community composition remains unrestored despite phosphorus addition. • Plant diversity is crucial for maintaining complex soil micro-food webs. • Modifying nitrogen/phosphorus ratio alone can't fully restore communities. [ABSTRACT FROM AUTHOR]

• Provide an ecological indicator to predict biotic and abiotic factors changes. • The ecosystem transition from alpine wetlands to meadows could be predicted by the indicator. • The indicator could be used in wetland restoration and management. The prospect of likely catastrophic transitions in ecosystems requires the development of early warning indicators that will provide advance warnings for undesired transitions. A grass hill is a unique microtopography that plays a crucial role in the functioning of wetland ecosystems. However, it is unclear whether grass hill size could serve as an important warning indicator to predict vegetation dynamics and ecosystem transitions during wetland degradation. Six degradation levels were selected along a grazing gradient in the alpine wetlands on the eastern Tibetan Plateau. General linear and segment regression were used to analyze whether grass hill area (GHA) can be used as an important warning indicator to predict biotic and abiotic factors and ecosystem transitions from typical alpine wetlands to meadows. The species diversity and biomass of aboveground vegetation increased slowly before the threshold point but decreased sharply after the threshold point (GHA (grass hill area) = 0.13 m2). The species diversity of both persistent and transient seed banks and the seed density of persistent seed banks also increased slowly but increased sharply before and after the threshold point (GHA = 0.2 m2). Soil moisture (SM), soil organic carbon (SOC) and total nitrogen (TN) decreased slowly but decreased sharply before and after the threshold point (GHA > 0.2 m2). Surprisingly, we also found the same threshold point (GHA = 0.13–0.2 m2) for the ecosystem transition from alpine wetlands to meadows as that for the other factors. GHA accurately predicted biotic (species diversity of vegetation and seed bank) and abiotic (SM, SOC, and TN) changes and the ecosystem transition from alpine wetlands to meadows. Thus, grass hill area is an effective warning indicator that could be used in future alpine wetland restoration and management. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to evaluate the role of seed bank during ecosystem transitions from arid grassland to shrubland. Methods: We explored the aboveground vegetation, seed bank and soil environmental factors at 29 sites along a moisture gradient that served as a space-for-time substitution in the Qaidam Basin on the Tibetan Plateau to test whether changes seed bank composition or changes in the ability of the seed bank to restore aboveground vegetation could lead to ecosystem transition. Results: We found that the composition of the aboveground vegetation presented nonlinear changes with decreased soil moisture and showed an inflection point in the threshold zone on the spatial scale of ecosystem transition from arid grassland to shrubland; however, an inflection point was not observed for the seed bank. Surprisingly, we also found the similarity between the aboveground vegetation and seed bank decreased obviously when soil moisture crosses the critical threshold. Conclusions: Our results suggest that the transition from arid grassland to shrubland ecosystem is not caused by changes of the seed bank composition but by the inhibition of the seed bank's restorability to aboveground vegetation. Future work on changes in vegetation composition and species diversity with ecosystem transitions should consider the belowground seed bank. [ABSTRACT FROM AUTHOR]

Background: With increased grazing disturbance of wetlands, soil moisture decreases, which could have an effect on the seed bank. The seed bank is a crucial resource for vegetation restoration; however, the effects of grazing disturbance on density and richness of seed banks and consequences on restoration of degraded wetlands are unclear. Methods: We selected six alpine wetlands along a degradation gradient on the Tibetan Plateau for study. The structural equation model was used to explore the direct and indirect effects of soil moisture on transient and persistent seed banks through soil physicochemical factors and vegetation. Non-metric multidimensional scaling was used to explore the role of seed banks in alpine wetland vegetation regeneration. Results: A decrease in soil moisture directly increased richness and density of the transient seed bank. However, decreased soil moisture indirectly decreased density of transient and increased richness and density of the persistent seed bank though soil pH and richness and abundance of vegetation. The similarity between the seed bank and vegetation increased with wetland degradation. Slope of the Bray-Curtis dissimilarity between transient seed bank and vegetation was higher than that for the persistent seed bank and vegetation. Conclusions: Transient seed banks remained almost constant under grazing disturbance, which favours persistent seed bank formation. Transient and persistent seed banks were determined by aboveground vegetation and soil environment, respectively. Seed banks provide strong resistance and resilience to degradation of wetland ecosystems, while persistent seed banks play a more important role than transient seed banks in restoration of degraded alpine wetlands. [ABSTRACT FROM AUTHOR]

Background and aims: If and how eutrophication influences the persistent soil seed bank is poorly understood. Here, we hypothesized that eutrophication alters the composition of the persistent seed bank indirectly through changes in the soil characteristics and aboveground plant community and productivity. We also hypothesized that changes in the persistent seed bank will consequently impact the aboveground vegetative composition. Methods: We tested these hypotheses using data from a 9-year nitrogen and phosphorus fertilization experiment in an alpine meadow ecosystem on the eastern Qinghai-Tibet plateau. Results: We found that long-term nitrogen and phosphorus fertilization indirectly impacted the composition of the persistent seed bank through changes in soil pH, aboveground vegetation composition and annual net primary productivity (ANPP). Changes in the composition of the persistent seed bank, however, were relatively minor in comparison to changes in aboveground vegetation composition. Finally, changes in the persistent seed bank did not feedback on aboveground vegetation composition. Conclusion: Our findings demonstrate the importance of soil pH, ANPP and vegetation composition in regulating the persistent seed bank under eutrophication. Our results also highlight the relative stability of the persistent seed bank to long-term eutrophication and their important contribution to the sustainability of grassland ecosystems. [ABSTRACT FROM AUTHOR]

Increased anthropogenic activities and global warming have accelerated the loss of wetlands worldwide. Given that a seed bank plays an important role in maintaining species diversity, understanding the regulatory mechanism of seed bank dynamics is crucial for using seed banks for restoration of species diversity in degraded wetlands. We collected data on biotic (i.e., aboveground vegetation, birds and rodents) and abiotic (i.e., soil environmental factors) ecosystem components as predictors along a degradation gradient in an alpine wetland and then to identify the relative importance of multiple sets of predictors in the regulating seed bank dynamics (i.e., species richness and composition). Seed bank dynamics were less responsive to environmental change than the aboveground vegetation during wetland degradation. Soil moisture and bird richness were more important than other predictors in regulating species richness and species composition of the seed bank, respectively. Our results suggest that seed banks can be used as potential resources for restoration of degraded wetlands. Birds play an important role in regulating the diversity of wetland ecosystems (seed bank is a potential diversity provider). Therefore, more attention should be paid to the protection of bird diversity in the process of conservation and restoration of degraded wetlands. • Seed banks can buffer the vegetation dynamic response to environmental change. • Seed bank dynamics are regulated by multiple ecosystem components. • Soil moisture and bird richness regulate seed bank diversity and composition. [ABSTRACT FROM AUTHOR]

Soil nematodes are important contributors to soil biodiversity. Nonetheless, the distribution patterns and environmental drivers of soil nematode communities are poorly understood, especially at the large scale, where multiple environmental variables covary. We collected 520 soil samples from 104 sites representing alpine meadow and steppe ecosystems. First, we explored the soil nematode community characteristics and compared community patterns between the ecosystems. Then, we examined the contributions of aboveground and belowground factors on these patterns. The genus richness and abundance of nematodes on the Tibetan Plateau are lower than other alpine ecosystems, but are comparable to desert or polar ecosystems. Alpine meadows supported a higher nematode abundance and genus richness than alpine steppes; bacterial-based energy channels were pre-dominant in both the ecosystems. Soil factors explained the most variation in the soil nematode community composition in the alpine meadows, while plant factors were as essential as soil factors in the alpine steppes. Unexpectedly, the climate variables barely impacted the nematode communities. This is the first study to explore the spatial patterns of soil nematode compositions on the Tibetan Plateau, and we found that the contributions of climate, plants, and soil properties on soil nematodes community were essentially different from the previous knowledge for well-studied plant and animal communities. [ABSTRACT FROM AUTHOR]

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 plants. Thus, studies on the effect of fluctuating temperature on germination at the community level are valuable for understanding community structure and biodiversity maintenance. We determined the effects of two alternating temperatures (5/25°C and 10/20°C) and one constant temperature (15°C) on seed germination of 445 species in a grassland community on the eastern Tibet Plateau. Seed mass was determined for each species, and data on habitat, type of life cycle, altitudinal distribution and functional group (graminoids or forbs) were obtained from the literature. Taking all species into account, alternating temperatures increased germination percentages regardless of amplitude. Overall, species growing in disturbed ground showed a significant germination response to temperature fluctuation, but those living in Alpine/subalpine meadow, forest margin /scrub, marshland and dry sunny slope habitats did not. 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. Germination of annuals/biennials was significantly promoted by 5/25°C, but not by 10/20°C, whereas germination of perennials was significantly promoted by both 5/25°C and 10/20°C. Small-seeded species were more likely than large-seeded species to respond positively to fluctuating temperatures. Germination of forbs had a positive response to temperature fluctuation, but germination of graminoids did not. Regeneration ability by seeds for about 36% of the species studied in the grassland can be increased by temperature fluctuation. The differential response among species to alternating vs. constant temperatures helps maintain community structure and biodiversity. A positive germination response to temperature fluctuation can partly explain why there are more forbs in degraded meadows. [ABSTRACT FROM AUTHOR]