Flooding, soil seed bank dynamics and vegetation resilience of a hydrologically variable desert floodplain

1. This paper explores soil seed bank composition and its contribution to the vegetation dynamics of a hydrologically variable desert floodplain in central Australia: the Cooper Creek floodplain. We investigated patterns in soil seed bank composition both temporally, in response to flooding (and drying), and spatially, with relation to flood frequency. Correlations between extant vegetation and soil seed bank composition are explored with respect to flooding. 2. A large and diverse germinable soil seed bank was detected comprising predominantly annual monocot and annual forb species. Soil seed bank composition did not change significantly in response to a major flood event but some spatial patterns were detected along a broad flood frequency gradient. Soil seed bank samples from frequently flooded sites had higher total germinable seed abundance and a greater abundance of annual monocots than less frequently flooded sites. In contrast, germinable seeds of perennial species belonging to the Poaceae family were most abundant in soil seed bank samples from rarely flooded sites. 3. Similarity between the composition of the soil seed bank and extant vegetation increased following flooding and was greatest in more frequently flooded areas of the floodplain, reflecting the establishment of annual species. The results indicate that persistent soil seed banks enable vegetation in this arid floodplain to respond to unpredictable patterns of flooding and drying.     

Characteristics of the soil seed bank in Mediterranean temporary ponds and its role in ecosystem dynamics

Species in temporary ponds overcome periods of unfavorable weather conditions by building up a large seed bank. With this strategy, the species diversity of ponds is preserved and information on their dynamics and structure is retained. Little is known about the characteristics, spatial patterns and role in the vegetation dynamics of the soil seed banks of Mediterranean temporary ponds, which are regarded as priority habitats under protection. We studied two sites of western Crete: Omalos, a mountain plateau at 1,060 m a.s.l. and Elafonisos, located near the coast at 60 m a.s.l. The seed bank was surveyed along transects using the germination method. Aboveground vegetation was measured on quadrats along the same transects. Canonical Correspondence Analysis (CCA) was run to define the zonation patterns. High density and species richness were recorded in both sites, with an average of 75,662 seeds/m² found in Omalos and 22,941 seeds/m² in Elafonisos. The community composition of both sites was remarkably different but in both locations perennial species were inconspicuous while annuals, prevailed in the seed banks. An important array of protected or rare species as well as several others which were absent from the vegetation were hosted in the soil seed banks, thereby rendering a low similarity between their composition. Soil seed banks in these ecosystems indicated a spatial heterogeneity that mirrored the aboveground vegetation distribution, sorted along the moisture gradient by their tolerance to flooding. Soil seed banks play a key role in the vegetation recovery after summer drought. The acts of preserving the soil seed bank and ensuring a transient flooding regime are essential to protect the unique vegetation communities of Mediterranean temporary ponds.     

土壤种子库的分类系统和种子在土壤中的持久性

对国际上已经发表的10个土壤种子库分类系统的内容进行了总结和阐述,并对土壤种子库分类系统进行了评述,其中Thompson ＆ Grime在1979年提出的把土壤种子库分为短暂土壤种子库（Transient soil seed bank）和持久土壤种子库（Persistent seed bank）的二元分类系统以及Thompson等人提出的把土壤种子库分为（1）短暂土壤种子库,（2）短期持久土壤种子库（Short term persistent seed bank）,（3）长期土壤种子库（Long termp ersistent seed bank）的三元分类系统在生态学文献中已被广泛采用。在此分类的基础上产生了植物种子在土壤中的持久性（Persistence）概念,持久性是指植物的一种特性,是指植物的种子在土壤中能够存活超过1a的特性;植物种子的持久性被认为是一种对环境的进化适应,它可以在多个生长季节萌发从而分担环境震荡的风险,持久土壤种子库不仅在不稳定的环境里占有优势;即使在稳定的环境里,也被认为能够减少种内和种间的竞争;造成持久性的原因可分为环境因子和种子本身的特性比如休眠等两个方面,持久土壤种子库的出现使得土壤种子库的研究与进化生物学结合起来,使得土壤种子库的研究进入一个新的领域,更易激发人们的兴趣。关于种子的大小、形状及持久性的关系问题已经引起了相当的争论,基本上有4种格局：一是种子大小和形状与种子在土壤中的持久性有关,小而圆或扁的种子在土壤易存活持久;二是种子大小与种子在土壤中的持久性有关,小种子在土壤中易存活持久,但种子形状与持久性无关;三是种子大小、形状与种子在土壤中的持久性无关;四为较大的种子在土壤易存活持久,而种子形状与种子在土壤中的持久性无关。影响种子在土壤中的持久性因子比较复杂,总结过去的文献发现主要有以下几个因子：①种子的散布方式,②捕食,③植被的物种组成,④风,⑤土壤基质,⑥火,⑦干扰等。通过比较分析和研究,提出影响种子大小和在土壤中的持久性关系格局的关键因子是气候,特别是生态系统所在地的雨量;湿润气候下容易产生前两种格局,而干旱环境下的生境容易产生后两种格局。     

Ecological correlates of seed persistence in soil in the north-west European flora

1 Using the data in a recently published seed bank database for north-west Europe, we describe how a species' seed bank behaviour can be characterized by a single 'longevity index', and investigate how representative the information in the database is of the north-west European flora. We also test the hypotheses that seeds of short-lived species are more persistent than those of long-lived species, and long-lived seeds are characteristic of species living in disturbed habitats.
2 The data are not representative of the north-west European flora as a whole; they are a fair reflection of a research effort that has been largely directed towards grassland and arable weeds. Data for rare species, non-agricultural habitats in general and wetlands, rocky habitats and native woodland in particular, are scarce or absent.
3 Annuals and biennials almost always have more persistent seeds than related perennials, and this difference is most striking when, as in Anagallis arvensis and Aphanes arvensis , the short-lived species have moved well away from the 'core' habitat of the family. Confamilial monocarps and polycarps do not differ consistently in seed mass.
4 Gradients of habitat disturbance are accompanied by predictable changes in seed persistence, which are themselves often (but not always) accompanied by parallel shifts in seed size. These results suggest that increasing habitat disturbance (i.e. increasing density-independent mortality) always selects for increased seed persistence, confirming both theory and previous analyses. However, increased seed persistence is not always associated with reduced seed size. This is because persistence depends not only on seed size, but on other traits, many of them physiological. In many habitats the probability of seed burial is strongly linked to seed size and shape, but in arable habitats cultural practices have broken this link.     

土壤种子库的研究进展及若干研究热点

 土壤种子库是指存在于表层土壤（包括凋落物）中的有生命的种子。土壤种子库的研究已是植物生态学研究不可缺少的一部分,现已成为植物种群生态学中比较活跃的领域。土壤种子库时期是植物种群生活史的一个重要阶段,有人称之为潜种群阶段。土壤种子库对一年生植物来说尤其重要。土壤种子库简单地可分为瞬时土壤种子库和长久土壤种子库,即使给予理想的萌发条件如季节、温度、湿度等,土壤种子库中也仍有部分种子保持休眠状态,休眠的种子组成了土壤长久种子库的成分。时空异质性是土壤种子库的基本特性之一,不仅不同植被类型的土壤种子库具有不同的组成、大小和多样性,而且微环境也影响土壤种子库的分布格局。由于萌发、捕食和衰老等原因,土壤种子库具有季节动态,一般在旧种子萌发之后,新种子散布之前达到最低点。在高等植物占据的大多数生境中,以休眠繁殖体形式存在的个体远远超过地上植株的数量;土壤种子库、幼苗库和成年植被相互联系相互影响。由于各种原因如群落类型的差异、群落的演替阶段、取样的时间等,地上植被和土壤种子库之间关系大体上可分为两种情况,即相似性和差异性;研究土壤种子库的方法通常有萌发法和物理分离法。土壤种子库能部分反应群落的历史,对退化生态系统的恢复起着重要的作用。目前土壤种子库的主要研究热点问题可分为以下几个方面：1）土壤种子库的研究方法,2）土壤种子库的分类问题,3）土壤种子库分布的时空格局,4）地上植被和土壤种子库的关系,5）土壤种子库的动态等。     

Dormancy cycling and persistence of seeds in soil of a cold desert halophyte shrub

Background and Aims

Formation of seed banks and dormancy cycling are well known in annual species, but not in woody species. In this study it was hypothesized that the long-lived halophytic cold desert shrub Kalidium gracile has a seed bank and dormancy cycling, which help restrict germination to a favourable time for seedling survival.

Methods

Fresh seeds were buried in November 2009 and exhumed and tested for germination monthly from May 2010 to December 2011 over a range of temperatures and salinities. Germination recovery and viability were determined after exposure to salinity and water stress. Seedling emergence and dynamics of the soil seed bank were investigated in the field.

Key Results

Seeds of K. gracile had a soil seed bank of 7030 seeds m⁻² at the beginning of the growing season. About 72 % of the seeds were depleted from the soil seed bank during a growing season, and only 1·4 % of them gave rise to seedlings that germinated early enough to reach a stage of growth at which they could survive to overwinter. About 28 % of the seeds became part of a persistent soil seed bank. Buried seeds exhibited an annual non-dormancy/conditional dormancy (ND/CD) cycle, and germination varied in sensitivity to salinity during the cycle. Dormancy cycling is coordinated with seasonal environmental conditions in such a way that the seeds germinate in summer, when there is sufficient precipitation for seedling establishment.

Conclusions

Kalidium gracile has three life history traits that help ensure persistence at a site: a polycarpic perennial life cycle, a persistent seed bank and dormancy cycling. The annual ND/CD cycle in seeds of K. gracile contributes to seedling establishment of this species in the unpredictable desert environment and to maintenance of a persistent soil seed bank. This is the first report of a seed dormancy cycle in a cold desert shrub.     

Seed bank dynamics in tall‐tussock grasslands along an altitudinal gradient

Abstract. We studied the germinable soil seed bank of tall‐tussock grasslands along an altitudinal gradient in the mountains of central Argentina. We selected 10 sampling plots at three altitudinal levels (1200 m, 1600 m and 2200 m). We assessed the composition of the established vegetation and took ten compound soil samples (0 ‐ 5 cm depth) at each plot in autumn and spring. The soil samples were sieved, chilled, and incubated in a glasshouse to assess the composition of the seed bank. The similarity between the composition of the seed bank flora and that of the established vegetation was low throughout the gradient. Most species did not change their seed bank strategy along the gradient. Seed bank richness and density increased with altitude. Most species had a persistent seed bank at all altitudinal levels, and the proportion of such species increased with altitude. These results suggest that a cold climate directly and/or indirectly favours the formation of seed banks and seed persistence in the soil.     

Impact of flooding on potential and realised grassland species richness

In order to reduce flood risk, river management policies advise floodplain restoration and the recreation of water retention areas. These measures may also offer opportunities for the restoration of species-rich floodplain habitats through rewetting and the restoration of flood dynamics. The potential to enhance biodiversity in such flood restoration areas is, however, still subject to debate. In this paper we investigate whether flooding along a small altered lowland river can contribute to the potential and realised species richness of semi-natural meadows. We compare the seed bank and vegetation composition of flooded and non-flooded semi-natural meadows and test the hypothesis that flooding contributes to an input of diaspores into the meadow seed banks, thereby promoting seed density and potential species richness. Furthermore we hypothesise that, where habitat conditions are suitable, flooding leads to a higher realised species richness. Results showed that seed densities in flooded meadows were significantly higher than in non-flooded meadows. The seed banks of flooded meadows also contained a higher proportion of exclusively hydrochorous species. However, the seed bank species richness, as well as the species richness realised in the vegetation did not differ significantly between flooded and non-flooded meadows. Finally, the seed bank and standing vegetation of flooded sites showed larger differences in species composition and Ellenberg nitrogen distribution than non-flooded sites. From these results we conclude that, although flooding does contribute to the density and composition of the seed bank, most imported seeds belong to only a few species. Therefore, it is unlikely that flooding substantially enhances the potential species richness. Furthermore, even if new species are imported as seeds into the seed bank, it seems unlikely that they would be able to establish in the standing vegetation. However, it is unclear which factors impede the establishment of imported species in the vegetation. The implications of our findings for flood meadow restoration are discussed.     

Seed bank persistence of clonal weeds in contrasting habitats: implications for control

The ability of weeds to form a seed bank is important for their population dynamics and management because it provides a refuge enabling reinvasion after established target plants have died. However, knowledge of the differential seed behaviour of individual species over multiple years and varying environmental conditions is surprisingly rare but necessary for effective control of diverse weed populations. We established a seed burial experiment in alpine habitats differing in management regime (i.e., forest, hay meadow and pasture) to determine whether seeds of the unpalatable perennial weeds, Veratrum album (white hellebore) and Gentiana lutea (yellow gentian) were able to delay germination and remain viable over 3 years. Our study shows that both species formed a short-term persistent seed bank; in the third-year, the soil seed banks of both species were nearly depleted, having declined to <5% of their original size. Both species had strikingly different germination strategies: G. lutea seeds mainly germinated in their first-year, whilst the majority of V. album seeds germinated in their second-year. The fraction of dormant G. lutea seeds increased with seed age, indicating that seeds remained viable after forgoing germination in the previous year. Habitat-specific differences in seed germination increased with seed age, with germination fractions being lowest in moist hay meadows. This suggests that the negative effects of anoxic conditions became more pronounced as seeds aged in hay meadows. Conversely, seed dormancy was equal among habitats. The absence of a long-term persistent seed bank has important implications for the management of both nuisance and endangered-plant populations. In the case of V. album and G. lutea, re-colonization of habitats from the seed bank is unlikely after established plants have been removed.     

Resilience,persistence and relationship to standing vegetation in soil seed banks of semi‐arid Australian old fields

Questions: Do soil seed banks of semi‐arid grasslands reassemble after abandonment from cultivation? Do seeds of native and exotic species persist in the soil? Does time since abandonment affect compositional similarity between the vegetation and seed bank? Does the seed bank contribute to resilience in the vegetation? Location: Native grasslands in northern Victoria, Australia. Methods: Seed bank sampling was conducted in spring and autumn over 3 yrs, across a 100‐yr chronosequence. Species richness, composition and germinant density were determined using the seedling emergence method. Seed persistence was assessed by comparing seed densities in spring and autumn. Seed bank composition was compared with the vegetation. Results: The spring seed bank was dominated at all stages by sedges and rushes; hence, native species richness and seed density were largely unaffected by abandonment. In autumn, grassland species contributed more to the seed bank, but richness was reduced after abandonment and showed little recovery, although seed density partially recovered. Seed bank composition showed some recovery in both seasons. Most species had low persistence in the soil. Compositional similarity between the vegetation and seed bank was greater in old fields than uncultivated grasslands in spring, but not autumn. Conclusions: Resilience varied among seed bank parameters and seed banks had low functional importance. Patterns in the seed bank followed, rather than caused, those in the vegetation. Thus, vegetation recovery cannot rely on the seed bank and persistent seeds were not the key mechanism of resilience in the vegetation.     

Climate change and bet-hedging: interactions between increased soil temperatures and seed bank persistence

In order to predict the long-term consequences of climate change, it is necessary to link future environmental changes to mechanisms that control plant population processes. This information can then be incorporated into strategies to more accurately model climate change impacts on species or to estimate future extinction risks. We examined the impact of increased temperatures on the longevity and dynamics of the persistent soil seed banks of eight ephemeral species from arid Australia. We found that the predicted global temperature increases under climate change will be reflected in increased soil temperatures, and that seeds in the soil seed bank will be exposed to long durations of high temperatures over the summer months. Three of the eight species studied had significantly greater levels of germination after exposure to predicted increased soil temperatures. Another species displayed a dramatic decrease in seed viability after such exposure. The capacity of such species to use the seed bank to bet hedge against rainfall events that cause germination but are insufficient to allow plant maturation, is compromised by increased germinability and subsequent loss or reduction of seed bank persistence. These predicted changes in the dynamics of soil seed banks increase the risk of local extinctions of these species, while the composition of the community may be altered by changes in species abundance. Our results show that the risk spreading mechanism provided by persistent seed banks could be compromised by the mechanistic impact of forecast temperature increases in arid habitats, and highlight the need to understand mechanisms that control population dynamics when attempting to address likely future impacts of climate change on biodiversity.     

A comparison of seed banks across a sand dune successional gradient at Lake Michigan dunes (Indiana,USA)

In habitats where disturbance is frequent, seed banks are important for the regeneration of vegetation. Sand dune systems are dynamic habitats in which sand movement provides intermittent disturbance. As succession proceeds from bare sand to forest, the disturbance decreases. At Indiana Dunes National Lakeshore, we examined the seed banks of three habitat types across a successional gradient: foredunes, secondary dunes, and oak savanna. There were differences among the types of species that germinated from each of the habitats. The mean seed bank density increased across the successional gradient by habitat, from 376 to 433 to 968 seeds m⁻², but with foredune and secondary dune seed bank densities being significantly lower than the savanna seed bank density. The number of seeds germinated was significantly correlated with soil organic carbon, demonstrating for this primary successional sequence that seed density increases with stage and age. The seed bank had much lower species richness than that of the aboveground vegetation across all habitats. Among sites within a habitat type, the similarity of species germinated from the seed banks was very low, illustrating the variability of the seed bank even in similar habitat types. These results suggest that restoration of these habitats cannot rely on seed banks alone.     

Seed banks on Attalea phalerata (Arecaceae) stems in the Pantanal wetland, Brazil

Background and Aims

Seeds can accumulate in the soil or elsewhere, such as on the stems of palms when these are covered by persistent sheaths. These sheaths could act as a safe site for some species. Here, we studied whether persistent sheaths of the palm Attalea phalerata (Arecaceae) are available sites for seed accumulation in the Pantanal wetland of Brazil. We also investigated whether the composition, richness and diversity of species of seeds in the persistent sheaths are determined by habitat (riparian forest and forest patches) and/or season (wet and dry).

Methods

All accumulated material was collected from ten persistent sheaths along the stems of 64 A. phalerata individuals (16 per habitat and 16 per season). The material was then individually inspected under a stereomicroscope to record seed species and number.

Key Results

Of the 640 sheaths sampled, 65 % contained seeds (n = 3468). This seed bank included 75 species belonging to 12 families, and was primarily composed of small, endozoochoric seeds, with a few abundant species (Cecropia pachystachya and Ficus pertusa). Moraceae was the richest family (four species) and Urticaceae the most abundant (1594 seeds). Stems of A. phalerata in the riparian forest had 1·8 times more seeds and 1·3 times more species than those in forest patches. In the wet season we sampled 4·1 times more seeds and 2·2 more species on palm stems than in the dry season. Richness did not differ between habitats, but was higher in the wet season. Abundance was higher in forest patches and in the wet season.

Conclusions

Attalea phalerata stems contain a rich seed bank, comparable to soil seed banks of tropical forests. As most of these seeds are not adapted to grow in flooding conditions, palm stems might be regarded as safe sites for seeds (and seedlings) to escape from the seasonal flooding of the Pantanal.     

Role of soil seed bank along a disturbance gradient in an alpine meadow on the Tibet plateau

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.     

Seed bank,seed size and dispersal in moisture gradients of temporary pools in Southern France

Plants reduce risk of extinction due to unpredictable rainfall by soil seed banks, dispersal or large seeds. However, seed size also increases independently in dry habitats, and since seed size is in a trade-off with seed number, size of seed banks is expected to increase in moister habitats. Therefore, we wanted to test if seed abundance in soil increases in wet habitats, if seed size increases in dry habitats, and if spread of seeds along the gradient is higher for plants of intermediate habitats in local moisture gradients.We studied 15 temporary pools in three biogeographically separated wetlands in Southern France. For each pool we studied five different moisture levels, totalling 75 local plant communities. We quantified soil seed bank by the seedling emergence method, seed size and an index of spatial spread of seeds in the soil for every species. We also quantified water levels for each plot.We found increasing abundance of seeds in the soil with increasing water levels but lower seed size and higher spread at intermediate water levels. When we controlled for niche position, we found no trade-off between seed size, spread and abundance in the soil seed bank.Type and importance of risk reduction strategies thus appeared to be strongly driven by the plant species’ moisture niche and the spatial arrangement of water levels.     

The contribution of persistent soil seed banks and flooding to the restoration of alluvial meadows

Restoration of species-rich flood meadows impoverished by agricultural intensification is an important challenge. The relationships between flooding regime and soil seed bank were compared in three successive meadow communities (hygrophilic, mesohygrophilic and mesophilic) distinguished along a topographic and hydric gradient. Differences in flood duration and frequency between the three associations allowed the study of the contribution of floods to soil seed bank richness and density. No significant difference was found in species richness among the three soil seed banks, whereas the densities were significantly higher in the wettest community. The three seed bank compositions were clearly distinguished along the hydric gradient. In fact, the three seed bank types constituted a species poor version of the meadow communities to which they belong. Flood contributions appear to play a minor role in seed bank enrichment. Thus, seed dispersal by flood water would probably be insufficient to enable the restoration of alluvial meadows.     

Drought and aquatic community resilience: the role of eggs and seeds in sediments of temporary wetlands

1. A long‐lived bank of propagules consisting of eggs, seeds and spores is one mechanism that allows aquatic communities to survive drought. A drying (drought) event is, for aquatic organisms in a temporary wetland, a phase from which communities must recover. Such a dry phase is often considered a disturbance but should not be considered adverse or catastrophic for the organisms that have evolved to live in temporarily wet habitats. 2. This paper explores the parallels between the egg bank of zooplankton and the seed bank of aquatic plants as means of survival in temporary wetlands. The resilience of communities in temporary wetland ecosystems is assessed by examining dormancy, hatching, germination, establishment and reproduction of animals and plants from the egg and seed banks of wetlands with a range of wetting and drying regimes. 3. Both the zooplankton and aquatic plants of the temporary wetlands studied rely on their egg and seed banks as a means for surviving drying. These communities recover after the disturbance of drying by means of specific patterns of dormancy, dormancy breakage, hatching, germination, establishment and reproduction. Spatial and temporal patterns of species richness allow resilience through dormancy, as not all species are present at all sites and not all species hatch and germinate at the same time. Multiple generations in the egg and seed bank and complexity of environmental cues for dormancy breakage also contribute to the ecosystem's ability to recover after a drying event. A persistent egg and seed bank allows species‐rich communities to hatch, germinate and develop rapidly once dormancy is broken. Rapid establishment of species‐rich communities that reproduce rapidly and leave many propagules in the egg and seed bank also facilitates community recovery on flooding of a temporary wetland after a drying event. 4. To maintain the diversity of temporary wetland communities through droughts and floods we need to manage the dry and wet phases of wetlands. To conserve a wide range of wetland types, we need to maintain a variety of hydrological patterns across the landscape.     

黄土丘陵沟壑区主要物种植冠种子库动态及其生态策略

植冠种子库是植物适应环境并应对外界干扰的种子生态策略之一,研究了黄土丘陵沟壑区12种主要植物植冠种子库动态,结果表明:杠柳不具有植冠种子库,其他11种植物均具有植冠种子库;除了黄刺玫种子在翌年5月达到脱落高峰,其他植物大部分种子在冬季脱落,其中杠柳、达乌里胡枝子、茭蒿、黄柏刺和水栒子的大部分种子脱落集中偏早,铁杆蒿和土庄绣线菊的大部分种子脱落集中偏晚;植冠宿存对大部分植物种子的萌发特性表现为促进作用;但不同植物种子的萌发时滞对植冠宿存响应差异较大;9种植物种子在植冠上宿存至翌年2月底,其种子活力仍能维持达60%以上;该区植物表现出不同的植冠种子库策略,通过不同的方式来减少干扰的威胁,提高成功萌发与更新的几率,它们或具有较大规模的宿存量、或调控种子萌发特性、或提高种子维持活力的百分比。此外,全面了解该区植物形成植冠种子库的机理及对应的生态策略还有待于全面、深入的研究。     

Soil seed bank dynamics in alpine wetland succession on the Tibetan Plateau

The primary goal was to address several questions with regard to how soil seed banks change in a successional series. How does the composition of the viable seed bank change, and how does the relationship of the soil seed bank and vegetation change with succession? Can the seed bank be regarded as a potential as a source of seeds for wetland restoration? We collected soil seed bank samples and sampled the vegetation in four different successional stages and used the NMDS (nonmetric multidimensional scaling) to evaluate the relationship of species composition between the seed banks and vegetation. The difference of seed density and species richness in different habitats and soil depths also was compared. Viable seeds of half (37) the species in the early-successional stage were found in all the successional stages. Similarity between seed bank and vegetation increased with succession. Both seed density and species richness in the seed bank increased with successional age and decreased with soil depth. The majority of species from the early-successional stage produced long-lived seeds. Seed density and species richness increased with succession, mainly as a result of increasing seed production, and hypotheses predicting decreasing density of buried seeds and species richness were not confirmed. Seed banks play a minor role in contributing to the regeneration of vegetation, and managers cannot rely on soil-stored seed banks for restoration of wetlands.     

The influence of vegetation,salinity, and inundation on seed banks of oligohaline coastal marshes

Sea level rise may alter salinity and inundation regimes and create patches of open water in oligohaline coastal marshes, potentially affecting the composition and germination of seed bank species. We conducted seedling emergence experiments to: (1) examine the effects of standing vegetation on the seed banks of three oligohaline marsh communities in coastal Louisiana (dominated by Paspalum vaginatum Sw., Sagittaria lancifolia L., or Spartina patens (Ait.) Muhl., respectively); and (2) investigate the effects of salinity and inundation regime on germination of seed bank species. We also studied the effect of a temporary increase in salinity (to simulate a salt water intrusion event) on the viability of buried seeds. We found that the presence or absence of vegetation within a community affected the abundance of some species in the seed bank but had little effect on species composition. Also, the seed banks of the three communities exhibited considerable overlap in species composition and had similar species richness (10–11) and diversity (antilog Shannon-Weaver diversity index = 6.5–7.1), despite differences in vegetation type. Higher salinities and flooding reduced seedling emergence for most species; few species emerged at salinities above four parts per thousand (ppt), and only Sagittaria lancifolia and Eleocharis parvula germinated well under flooded conditions. A temporary increase in salinity did not affect species richness or seedling emergence of most species. Our results suggest that differences in vegetation may have little effect on the composition of seed banks of oligohaline marshes. However, higher salinities and greater depth and duration of inundation (anticipated as global sea level continues to rise) may decrease recruitment of seed bank species, reducing their abundance in oligohaline marsh communities.