Effects of Acmella radicans Invasion on Soil Seed Bank Community Characteristics in Different Habitats.

To examine the effects of the recent Acmella radicans invasion on plant community and diversity in invaded habitats, the composition, density, species richness, diversity indices, and evenness index of the soil seed bank community of two different habitats (wasteland and cultivated land) in Yunnan Province, China, were analyzed through field sampling and greenhouse germination tests. A total of 28 species of plants belonging to 15 families and 28 genera, all annual herbs, were found in the soil seed bank. Seed densities and species number in the seed bank tended to be greater in April than in October; cultivated land also featured higher seed densities and species numbers compared to wasteland. With increased A. radicans cover, the seed bank population of A. radicans also significantly increased, but the seed bank populations of many other dominant species (e.g., Ageratum conyzoides and Gamochaeta pensylvanica) and native species (e.g., Laggera crispata and Poa annua) clearly declined. The germination of A. radicans seeds was concentrated during the period from the 4th to the 5th weeks. Vertically, the seed number of A. radicans was significantly different among the 0-5 cm, 5-10 cm and 10-20 cm layers that accounted for 80.7-90.6%, 9.4-16.1% and 0.0-3.2% of the total seed density in wasteland, respectively; and in cultivated land, A. radicans accounted for 56.8-64.9%, 26.7-31.8% and 8.1-13.5% of the total seed density, respectively. With reduced A. radicans cover, the species richness, Simpson index, Shannon-Wiener index, and Pielou indices of the weed community generally increased, and most diversity indices of weed communities in cultivated land were lower than in wasteland under the same cover of A. radicans. The results indicate that the invasion of A. radicans has negatively affected local weed community composition and reduced weed community diversity, and that these negative impacts in cultivated land may be enhanced by human disturbance. Our study was the first to elucidate the influence of A. radicans invasion on soil seed bank community characteristics in invaded habitats, providing a better understanding of its invasion and spread mechanisms in order to aid in developing a scientific basis for the prevention and control of this invader.

Seed germination requirements of the rare Helosciadium repens (aka Apium repens) determine persistence of seeds in the soil seed bank.

The rare and threatened Heliosciadium repens grows in moist grasslands and has a distinct life cycle. Plants reproduce both clonally, although ramets tend to be short-lived, and sexually, with seeds that can form a persistent soil seed bank. The germination requirements of H. repens were investigated, yielding important information for its habitat management and conservation. We examined the soil seed bank in three populations and carried out germination experiments and embryo growth measurements with fresh seeds in laboratory, greenhouse and outdoor conditions. We also investigated the effects of storage and burial of seeds. H. repens formed a long-term persistent (>6 years) soil seed bank with very pronounced primary dormancy, but no secondary dormancy or dormancy cycles. Seeds can germinate throughout the growing season when temperatures are sufficiently high. Embryo growth and seed germination are triggered by light and, to a lesser extent, daily temperature fluctuations. Seeds of H. repens seem to have developed a unique germination syndrome with several strategies to remain dormant in the soil until optimal conditions are present for seedling establishment and survival. Both sexual reproduction and seed bank formation are crucial for the long-term survival of the populations.

[Effects of water level on soil seed bank in the floodplain wetland of Juzhang River, China]. / 水位变化对沮漳河河漫滩湿地土壤种子库的影响.

Aiming to understand the responses of soil seed bank to different water levels, we investigated vegetation and soil seed bank along a water level gradient (frequently flooded area, unflooded area) on the floodplain wetland of Juzhang River. We used the structural equation model to explore the direct and indirect effects of water level on soil seed bank, and used non-metric multidimensional scaling (NMDS) to assess the role of soil seed bank for vegetation regeneration. The results showed that the density of transient and persistent seed banks at unflooded area was 36.9% and 7.8% higher than that of frequently flooded area, respectively. Shannon index and Pielou index of seed bank and vegetation were significantly affected by water level and sampling location. Water level significantly affected the similarity between seed bank and aboveground vegetation, and the similarity of persistent seed bank with aboveground vegetation was significantly higher than that with transient seed bank. Structural equation model showed that water level had a direct effect on seed bank density, and indirect effects on density and richness of seed bank via affecting soil pH and NH4+-N content. NMDS results showed that there was no significant difference in the composition of the persistent seed bank and vegetation community in autumn under different water levels, but water level significantly changed the community composition of transient seed bank. Transient seed bank was affected by the vegetation and soil property, while persistent seed bank was determined by aboveground vegetation and water level. Although soil seed bank had low regeneration potential for the vegetation communities in floodplain wetlands, soil seed bank could not be neglected during the restoration of propagule diversity after disturbance in wetlands. Persistent seed bank would be an importance source of diversity of propagules for floodplain wetlands restoration following disturbance.

[Effects of coal mine waste dump on soil seed bank and vegetation distribution pattern]. / ç ¤çŸ¿æŽ’çŸ¸åœºå¯¹å‘¨è¾¹åœŸå£¤ç§å­åº“åŠæ¤è¢«åˆ†å¸ƒæ ¼å±€çš„å½±å“.

Long-term occupation of coal gangue dumping sites (CGDS) may destroy ecological environment of nearby area. However, how the CGDS affects the distribution pattern of soil seed banks and vegetation in the nearby area is not clear. In this study, we investigated soil seed bank and vegetation at different distances from the second CGDS of Yangchangwan in Ningdong mining area, Lingwu, Ningxia. The results showed that soil seed bank was mainly distributed in 0-10 cm layer and decreased with increasing soil depth. Species richness of soil seed bank and vegetation first increased and then tended to be stable with increasing distance to the CGDS. The influence range of CGDS on soil seed banks was 300-500 m and was 100-300 m on aboveground vegetation. The CGDS did not affect the vertical distribution pattern of soil seed bank, but significantly affected the horizontal distribution pattern of soil seed banks and aboveground vegetation. The key area of vegetation restoration around the CGDS was between 100 m and 300 m.

A long-term experiment reveals no trade-off between seed persistence and seedling emergence.

Information on seed persistence and seedling emergence from the soil seed bank is critical for understanding species coexistence and predicting community dynamics. However, quantifying seed persistence in the soil is challenging; thus, its association with other life-history traits is poorly known on a broad scale. Using germination phenology for 349 species in a 42-yr experiment, we quantified the persistence-emergence correlations and their associations with intrinsic regeneration traits using Bayesian phylogenetic multilevel models. We showed no trade-off between seed persistence and seedling emergence. Physically dormant seeds were more persistent but exhibited lower emergence than nondormant seeds. Monocarpic species had both higher persistence and emergence than polycarpic species. Seed mass posed a marginal proxy for persistence, while emergence almost doubled from the smallest to the largest seeds. This study challenges the traditional assumption and is the first demonstration of noncorrelation between persistence and emergence, probably owing to the complexity of regenerative strategies. Species with short persistence and low emergence would be the most vulnerable for in situ conservation. Our analyses of this unique, long-term dataset provide a strong incentive for further experimental studies and a rich data resource for future syntheses.

Decoupled responses of above- and below-ground beta-diversity to nitrogen enrichment in a typical steppe.

Increased atmospheric nitrogen (N) deposition affects biodiversity in terrestrial ecosystems. However, we do not know whether the effects of N on above-ground plant ß-diversity are coupled with changes occurring in the soil seed bank. We conducted a long-term N-addition experiment in a typical steppe and found that above-ground ß-diversity increased and then decreased with increasing N addition, whereas below-ground ß-diversity decreased linearly. This suggests decoupled dynamics of plant communities and their soil seed bank under N enrichment. Species substitution determined above- and below-ground ß-diversity change via an increasing role of deterministic processes with N addition. These effects were mostly driven by differential responses of the above-ground vegetation and the soil seed bank ß-diversities to N-induced changes in environmental heterogeneity, increased soil inorganic N concentrations and soil acidification. Our findings highlight the importance of considering above- and below-ground processes simultaneously for effectively conserving grassland ecosystems under N enrichment.

Snow, fire and drought: How alpine and treeline soil seed banks are affected by simulated climate change.

BACKGROUND AND AIMS: Seed persistence in soil depends on environmental factors that affect seed dormancy and germination, such as temperature and water availability. In high-elevation ecosystems, rapid changes in these environmental factors due to climate change can impact future plant recruitment. To date, our knowledge on how soil seed banks from high-altitude environments will respond to climate change and extreme climate-related events is limited. Here, using the seedling emergence method, we investigated the effects of reduced snow cover, fire and drought on the density and diversity of germinants from soil seed banks of two high-altitude plant communities: a tall alpine herbfield and a treeline ecotone. METHODS: In Autumn 2020, we collected soil samples and characterized the standing vegetation of both communities at Kosciuszko National Park, Australia. Then, we employed a factorial experiment and subjected the soil samples to a series of manipulative treatments using greenhouse studies. KEY RESULTS: The treeline had a larger and more diverse soil seed bank than the herbfield. A reduction in snow had a negative effect on the number of germinants in the herbfield and increased the dissimilarity with the standing vegetation, while the treeline responses were mainly neutral. Fire did not significantly affect the number of germinants but decreased the evenness values in both communities. The drought treatment reduced the number and richness of germinants and increased the dissimilarity with the standing vegetation in both communities. Plant functional forms explained some of the detected effects but seed functional traits did not. CONCLUSIONS: Our study suggests that simulated climate change will affect plant recruitment from soil seed banks in a variety of ways. Changes in snow cover, incidences of fire and drought may be key drivers of germination from the soil seed bank and therefore the future composition of alpine plant communities.

The 141-year period for Dr. Beal's seed viability experiment: A hybrid surprise.

PREMISE: In 1879, Dr. William Beal buried 20 glass bottles filled with seeds and sand at a single site at Michigan State University. The goal of the experiment was to understand seed longevity in the soil, a topic of general importance in ecology, restoration, conservation, and agriculture, by periodically assaying germinability of these seeds over 100 years. The interval between germination assays has been extended and the experiment will now end after 221 years, in 2100. METHODS: We dug up the 16th bottle in April 2021 and attempted to germinate the 141-year-old seeds it contained. We grew germinants to maturity and identified these to species by vegetative and reproductive phenotypes. For the first time in the history of this experiment, genomic DNA was sequenced to confirm species identities. RESULTS: Twenty seeds germinated over the 244-day assay. Eight germinated in the first 11 days. All 20 belonged to the Verbascum genus: Nineteen were V. blattaria according to phenotype and ITS2 genotype; and one had a hybrid V. blattaria × V. thapsus phenotype and ITS2 genotype. In total, 20/50 (40%) of the original Verbascum seeds in the bottle germinated in year 141. CONCLUSIONS: While most species in the Beal experiment lost all seed viability in the first 60 years, a high percentage of Verbascum seeds can still germinate after 141 years in the soil. Long-term experiments such as this one are rare and invaluable for studying seed viability in natural soil conditions.

Effects of different grassland utilization methods on the germinable soil seed bank of the Hulunbuir meadow steppe.

Seed banks are crucial regenerative resources for aboveground vegetation. The pattern of their changes holds immense significance in understanding alterations in the belowground seed bank. This understanding is pivotal for uncovering both short-term and long-term shifts in plant communities. Additionally, it contributes to the restoration of grassland ecosystems. To better protect grassland biodiversity and provide a theoretical basis for the restoration of degraded grasslands, in this study, the germination characteristics of soil seed banks in free-grazed, enclosed and mown areas were compared, and the results were combined with those of previous studies for a comprehensive analysis. The density of soil seed bank and perennial forage soil seed bank were significantly affected by different grassland utilization and soil depths. Grazing and enclosure grassland utilization methods increased the content of the soil seed bank, and mowing reduced the content of the seed bank. The soil seed bank density of perennial grasses accounted for the highest proportion under grazing, followed by mowing, and its lowest proportion was observed in the enclosures. Grazing not only facilitated the germination of the perennial grass seed bank but also substantially augmented its content. Mowing inhibited the germination of the upper growth grasses seed bank, which was particularly significant in the 0-2 cm soil layer under grazing. The content of the upper growth grasses seed bank affected the total seed bank to a certain extent, mainly in the 5-10 cm layer. The general correlations among the perennial grasses, upper growth grasses and soil germination seed bank resulted in 84.58% information extraction, and this information has practical significance for grassland ecological restoration.

Diversity of soil seed bank and influencing factors in the nascent wetland of the Yellow River Delta.

Soil seed bank is the growth and reproduction source of vegetation community, playing an important role in vegetation establishment, succession and renewal, biodiversity maintenance. This study has selected the nascent wetland in the Yellow River Delta (YRD) formed in 1996 as study area and investigated the diversity and key influencing factors of soil seed bank diversity. The study results show that: (1) The soil seed bank in the study area has a simple structure, containing relatively few species. A total of five plant species, which belong to four families and five genera, were found in this bank, with Phragmites australis and Suaeda salsa being the dominant plants. (2) All species are herbs without woody species. One herb is annual herb and the others are perennial herbs. (3) From the sea to the river, the changes rules of the overall density and diversity of the seed bank are not obvious. (4) The dispersal distance from salt and freshwater has a significant influence on the density of the soil seed bank but has no significant influence on the diversity. Meanwhile, the soil salt content has a significant negative influence on the diversity of seed banks. (5) Aboveground vegetation did not closely relationship with diversity of soil seed bank. All above results can provide basic data and scientific evidence for the conservation of vegetation communities in the nascent wetlands and vegetation restoration in the degraded wetlands in the YRD.

A source of hidden diversity: soil seed bank and aboveground populations of a common herb contain similar levels of genetic variation.

In many landscapes, successful re-establisment of plant populations depends on the presence of diaspores, either near or directly beneath sites to be restored. The soil seed bank is, therefore, an important part of ecosystem resilience and a vital pillar for regeneration of genetic diversity in many plant populations. However, regeneration from the soil seed bank and the siubsequent restoration can only be considered successful when genetic diversity of restored populations is not eroded nor genetic differentiation inflated. We compared genetic variation within and among soil seed bank and aboveground populations of Origanum vulgare, to test whether genetically variable populations can be restored from the soil seed bank. We explored levels of genetic diversity within aboveground populations and the corresponding soil seed banks. Furthermore, we assessed the extent to which the soil seed bank differs genetically from the aboveground population. Levels of genetic diversity were to generally similar in aboveground populations and the corresponding soil seed banks. Only levels of inbreeding were slightly higher in the lower layer of the soil seed bank compared to the aboveground populations, probably because of selection processes acting against homozygotes accumulating in the seed bank. Furthermore, significant genetic differentiation between the aboveground population and the corresponding seed banks was completely absent. Across all sites, genetic differentiation between the soil seed bank was similar to that between aboveground populations, probably due to the absence of severe climate conditions, strong bottlenecks or disturbance events. Our conclusions support the possibility of successful re-establishment of healthy, genetically variable plant populations after aboveground destruction or following soil re-allocation from persistent seed banks.

Spatial variation of soil seed banks along a gradient of anthropogenic disturbances in tropical forests on coral islands.

Poor regeneration of natural vegetation is a major factor contributing to the degradation of tropical coral islands. Soil seed banks (SSB) are important for maintaining the resilience of plant communities. However, the community characteristics and spatial distribution of SSBs and the controlling factors along human disturbance on coral islands are unclear. To fill this gap, we measured the community structure and spatial distributions of forest SSBs on three coral islands in the South China Sea, with varying degrees of human disturbance. The results showed that strong human disturbance increased the diversity, richness, and density of SSBs, as well as increased the richness of invasive species. With increased human disturbance, the heterogeneity pattern of SSBs spatial distribution changed from difference between forest east and west to forest center and edge. The similarity between the SSBs and above-ground vegetation also increased, and the distribution of invasive species extended from the edge to the central area of the forests, demonstrating that human disturbance limited the outward dispersal of seeds of resident species but increased the inward dispersal of seeds of invasive species. Interaction between soil properties, plant characteristics, and human disturbance explained 23-45% of the spatial variation of forest SSBs on the coral islands. However, human disturbance reduced the correlations of plant communities and spatial distribution of SSBs with soil factors (i.e., available phosphorus and total nitrogen) and increased the correlations of the community characteristics of SSB with landscape heterogeneity index, road distance, and shrub and litter cover. Resident seed dispersal on tropical coral islands might be enhanced by reducing building height, constructing buildings in down-wind locations, and preserving corridors that support animal movement among forest fragments.

Epiphytic and Endophytic Fungi Colonizing Seeds of Two Poaceae Weed Species and Fusarium spp. Seed Degradation Potential In Vitro.

Fungi colonizing the surface and endosphere of two widespread Poaceae weed species, Avena fatua and Echinochloa crus-galli, were isolated to compare the taxonomic composition between the plant species, location, and year of the seed collection. The seed-degrading potential of Fusarium isolated from the seeds was tested by inoculating seeds of E. crus-galli with spore suspension. Molecular identification of epiphytic and endophytic fungal genera was performed by sequencing the ITS region of rDNA. Endophytes comprised of significantly lower fungal richness compared to epiphytes. A significant taxonomic overlap was observed between the endosphere and seed surface. The most abundant genera were Alternaria, Fusarium, Cladosporium, and Sarocladium. Analysis of similarities and hierarchical clustering showed that microbial communities were more dissimilar between the two plant species than between the years. Fusarium isolates with a high potential to infect and degrade E. crus-galli seeds in laboratory conditions belong to F. sporotrichioides and F. culmorum.

Light controls alpine meadow community assembly during succession by affecting species recruitment from the seed bank.

Some research indicates that soil seed banks can promote species coexistence through storage effects. However, the seed bank mechanism that maintains plant assembly and its role in degraded grassland restoration are still not clear. We collected seed bank samples from early, mid and late secondary successional stages of an abandoned subalpine meadow on the Tibetan Plateau, and samples from each stage were exposed to full (i.e., natural), mid, and low light treatments in the field to represent light availability at the bottom/understory (soil surface) of a plant community in the early, mid and late stages of succession, respectively. Species richness, seed density, species composition, and community weighted mean values (CWMs) of seed mass of the species whose seeds germinated in soil samples were evaluated. In response to the light treatments, species richness increased significantly with increased light only for the late successional stage, seed density increased significantly with increased light only in the early and mid successional stages, and seed mass decreased significantly with increased light only in the mid and late successional stages. Species composition differed significantly among the light treatments only in the late successional stage. For the successional series, species richness and seed mass of the species that germinated increased significantly with succession only under mid and full light treatments. Seed density decreased significantly with succession in each light treatment. Species composition differed significantly between the early- and late stage and between the mid and late stage in each light treatment. Both the abiotic (light) and biotic (seed mass) factors influence seed bank recruitment to the plant community. Regeneration of small-seeded species in the seed bank was inhibited under low light in the late successional stage. The balance of stochastic and deterministic processes along a successional gradient was determined by regeneration from the seed bank depending on light intensity change. Differences in seed response to light intensity change largely determined plant community assembly. Our findings should help in the development of effective conservation and restoration strategies.

Soil seed bank distribution and restoration potential in the vegetation of Buska Mountain range, Hamar district, southwestern Ethiopia.

The seed banks are vital components for the reestablishment of degraded lands since they are used to predict the future coverage of vegetation and allow for the implementation of appropriate conservation measures in a particular area. The study was conducted in the Buska Mountains of the Hamar area in south-western Ethiopia and determined the composition, density and vertical distribution of soil seed banks under various land-use systems and soil layers. A total of 96 soil samples were involved in the study; four land-use types (grassland, forest, scrub and bare ground). Three distinct soil layers from each plot (0-3 cm, 3-6 cm, 6-9 cm depths) were sampled. Jaccard's Similarity Coefficient was applied to evaluate the correspondence between different land-use types and soil layers. One-way ANOVA was used to compute species density and composition respectively within land-use systems along with the seed bank and above ground vegetation. Fifty six (56) species within 27 plant families and 50 genera were recorded. Twenty percent of the species was contributed by Asteraceae followed by Poaceae (16%). Herbaceous growth forms were the most dominant in the area, contributing about 78.6%. The total seedling density in the study plots was 8171 seedlings/m2. Jaccard's Similarity Coefficient is relatively higher (0.52) between grassland and scrub, while the forest and bare land had the least amount of similarity (0.22). There was seen a higher similarity of species between the first and second soil layers and a decreasing density with soil depth. A substantial difference between the aboveground species and seed bank was recorded in the area. The lower resemblance between the standing vegetation and the seed bank infers a lower overall restoration potential and suggests other alternative regeneration mechanisms such as seedling plantation of priority indigenous plant species and avoiding anthropogenic disturbances.

Long-term Spartina alterniflora invasion simplified soil seed bank and regenerated community in a coastal marsh wetland.

The coastal wetland is easily invaded by alien species due to locating in the land and sea transitional area. As a potential driving regeneration force, the soil seed bank is vital to the community restoration and species diversity protection. To reveal the long-term Spartina alterniflora invasion impact on the soil seed banks and regenerated communities, we investigated the seed banks under the different vegetation types (S. alterniflora, Phragmites australis, Scirpus mariqueter, ruderal and unvegetated site) and soil depths (0-5 and 5-10 cm) in the coastal salt marsh wetland, Chongming island, eastern China. The results showed that the soil seed bank richness and species density under different vegetation types were higher than the aboveground vegetation, and those of 0-5 cm seed banks were higher than 5-10 cm, except for the unvegetated site. The species richness and S. alterniflora seed proportion in the seed banks under S. alterniflora communities (S.AS) were lower and larger respectively than those of other sites. The species composition between S.AS and the aboveground communities showed high similarity with aggregation phylogenetic structures in two soil depths. The seed bank variations at 0-5 and 5-10 cm depths were interpreted 3.03% and 2.25% by the aboveground communities, while 4.92% and 5.55% were interpreted by the soil microbial biomass. The SEM model explained 98.1% and 91.8% of the seed banks richness at the 0-5 cm depth and 5-10 cm depth, respectively, and explained 98.8% and 46.1% of the seed banks species density at the 0-5 cm depth and 5-10 cm depth, respectively. The aboveground vegetation biomass and abundance directly affected the 0-5 cm seed banks richness and species density, while its height and biomass only affected the 5-10 cm seed banks species density. The 0-10 cm soil depth microbial biomass indirectly affected the 0-5 cm seed banks richness and species density, while affected the 5-10 cm seed banks richness. Soil physical and chemical properties only indirectly affected the 0-5 cm seed banks species density. The results provided a reference for the ecological evaluation of the impacts of S. alterniflora invasion into the coastal salt marsh wetland of eastern China, and guidance for the protection and restoration of the native plant communities.

[Diversity of soil seed banks under different vegetation types in the southeastern margin of the Tengger Desert, China]. / è ¾æ ¼é‡Œæ²™æ¼ ä¸œå—ç¼˜ä¸åŒæ¤è¢«ç±»åž‹åœŸå£¤ç§å­åº“å¤šæ ·æ€§.

To explore the dynamics and distribution of soil seed banks under different vegetation types in desert, and reveal the community succession tendency and diversity characteristics of different vegetative types, we took Populus euphratica community, Caragana intermedia community, Leymus secalinus community and Agriophyllum squarrosum community as the research objects in the southeastern margin of the Tengger Desert. Samples of 0-2 cm, 2-5 cm, 5-10 cm, and 10-20 cm soil layers were collected. We examined the characteristics of soil seed banks and their relationships with vegetation. The results showed that there were 13 plant species in the soil seed banks of the four vegetation types, belonging to 3 families and 12 genera, with the annual and biennial herbs dominated and much Chenopodiaceae species. The soil seed bank density was generally low, with an order of C. intermedia community > L. secalinus community > P. euphratica community > A. squarrosum community. The seed bank density and species richness decreased with increasing soil depth. Based on the Shannon index, Simpson index, Pielou index and Patrick richness analysis, the order of species diversity in soil seed banks was P. euphratica community > L. secalinus community > C. intermedia community > A. squarrosum community. The similarity coefficient between soil seed bank and vegetation was the highest in C. intermedia community, followed by P. euphratica community, and the lowest in P. euphratica community and L. secalinus community. On the whole, the arbor forest P. euphratica community was the most stable one, while the sandy land A. squarrosum community was the most vulnerable.

Vertical distribution of soil seed bank and the ecological importance of deeply buried seeds in alkaline grasslands.

Background: Soil seed banks play a central role in vegetation dynamics and may be an important source of ecological restoration. However, the vast majority of seed bank studies examined only the uppermost soil layers (0-10 cm); hence, our knowledge on the depth distribution of seed bank and the ecological significance of deeply buried seeds is limited. The aim of our study was to examine the fine-scale vertical distribution of soil seed bank to a depth of 80 cm, which is one of the largest studied depth gradients so far. Our model systems were alkaline grasslands in East-Hungary, characterised by harsh environmental conditions, due to Solonetz soil reference group with Vertic horizon. We asked the following questions: (1) How do the seedling density and species richness of soil seed bank change along a vertical gradient and to what depth can germinable seeds be detected? (2) What is the relationship between the depth distribution of the germinable seeds and the species traits? Methods: In each of the five study sites, four soil cores (4 cm diameter) of 80 cm depth were collected with an auger for soil seed bank analysis. Each sample was divided into sixteen 5-cm segments by depth (320 segments in total). Samples were concentrated by washing over sieves and then germinated in an unheated greenhouse. Soil penetration resistance was measured in situ next to each core location (0-80 cm depth, 1-cm resolution). We tested the number and species richness of seedlings observed in the soil segments (N = 320), using negative binomial generalized linear regression models, in which sampling layer and penetration resistance were the predictor variables. We ran the models for morphological groups (graminoids/forbs), ecological groups (grassland species/weeds) and life-form categories (short-lived/perennial). We also tested whether seed shape index, seed mass, water requirement or salt tolerance of the species influence the vertical distribution of their seed bank. Results: Germinable seed density and species richness in the seed bank decreased with increasing soil depth and penetration resistance. However, we detected nine germinable seeds of six species even in the deepest soil layer. Forbs, grassland species and short-lived species occurred in large abundance in deep layers, from where graminoids, weeds and perennial species were missing. Round-shaped seeds were more abundant in deeper soil layers compared to elongated ones, but seed mass and ecological indicator values did not influence the vertical seed bank distribution. Our research draws attention to the potential ecological importance of the deeply buried seeds that may be a source of recovery after severe disturbance. As Vertisols cover 335 million hectares worldwide, these findings can be relevant for many regions and ecosystems globally. We highlight the need for similar studies in other soil and habitat types to test whether the presence of deep buried seeds is specific to soils with Vertic characteristics.

Seed Germination and Seed Bank Dynamics of Eruca sativa (Brassicaceae): A Weed on the Northeastern Edge of Tibetan Plateau.

As a versatile cruciferous species, Eruca sativa is widely cultivated, but in some areas, it has become an invasive weed. There are few studies on its seed dormancy and soil seed bank. This research examined seed dormancy, germination, and dynamics of the soil seed bank of E. sativa, with a view to provide support for its prevention and control. We tested the effects of temperature, light, storage, water, and salinity stress on seed germination and burial depth on seedling emergence of E. sativa. Dynamics of the soil seed bank were determined with a 24 month in situ seed-burial study. Seeds of E. sativa can germinate in a temperature range of 5-35°C; moreover, they exhibited non-deep physiological dormancy (NDPD) at maturity, which can be broken by dry storage or exposure to low temperature in winter. Germination of E. sativa seeds was sensitive to water and salinity stress, and most seeds did not germinate at -0.3 MPa. When buried in soil in the field, seeds exhibited an annual dormancy/non-dormancy cycle and formed at least a short-term persistent soil seed bank. Seeds buried deeper than 5 cm can hardly emerge. Seeds of E. sativa have a wide germination temperature range and exhibited dormancy cycling, which promotes the formation of a persistent soil seed bank and enables it to better adapt to the harsh low-temperature climate of the Qinghai-Tibet Plateau. No-tillage would be a good management strategy for this species.