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。     

Alpine species seed longevity in the soil in relation to seed size and shape – A 5-year burial experiment in the Central Alps

Long-term persistent seeds are generally expected to be small and spherically shaped. In contrast, transient seeds are often large, flattened and elongated. We hypothesized that alpine species follow these trends, and that most species of unstable alpine habitats have the potential to form long-term persistent seed banks. The latter would enable them to delay germination until favourable conditions are present in their environment thereby increasing the likelihood for establishment of seedlings. We selected nine alpine species of more or less unstable habitats (i.e. Achillea moschata, Artemisia genipi, Anthyllis vulneraria ssp. alpicola, Geum reptans, Linaria alpina, Oxyria digyna, Saxifraga aizoides, Saxifraga oppositifolia, and Trifolium pallescens) for this study. Seed longevity was estimated by a 5-year burial experiment in the field with seed excavations after 1 winter, 2 years and 5 years. Germination experiments in the growth chamber and viability tests were performed after each excavation. We detected longevity patterns ranging from transient to long-term persistent. Two species were classified as transient. All other species have the potential to form persistent seed banks, with almost half of the investigated species showing a trend for long-term persistence. Despite contradictory reports, long-term persistent seed banks are an important life history trait of species of unstable alpine habitats. We found that seed shape and hard-seededness are good predictors of seed persistence of alpine species. Seed size seems to be less important. The data from this study support the general hypotheses describing the relationship among seed size, seed shape and seed persistence in the soil.     

Burial increases seed longevity of two Artemisia tridentata (Asteraceae) subspecies

? Premise of the study: Seed longevity and persistence in soil seed banks may be especially important for population persistence in ecosystems where opportunities for seedling establishment and disturbance are unpredictable. The fire regime, an important driver of population dynamics in sagebrush steppe ecosystems, has been altered by exotic annual grass invasion. Soil seed banks may play an active role in postfire recovery of the foundation shrub Artemisia tridentata, yet conditions under which seeds persist are largely unknown. ? Methods: We investigated seed longevity of two Artemisia tridentata subspecies in situ by retrieving seed bags that were placed at varying depths over a 2 yr period. We also sampled naturally dispersed seeds in litter and soil immediately after seed dispersal and before flowering in subsequent seasons to estimate seed persistence. ? Key results: After 24 mo, seeds buried at least 3 cm below the soil surface retained 30-40% viability whereas viability of seeds on the surface and under litter declined to 0 and < 11%, respectively. The density of naturally dispersed seeds in the seed bank was highly heterogeneous both spatially and temporally, and attrition varied significantly by region. ? Conclusions: Our study suggests that Artemisia tridentata has the potential to form a short-term soil seed bank that persists longer than has been commonly assumed, and that burial is necessary for seed longevity. Use of seeding techniques that promote burial of some seeds to aid in formation of a soil seed bank may increase restoration potential.     

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.     

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 strategies in Patagonian semi-arid grasslands in relation to their management and conservation

We addressed the following questions: (a) May different seed bank functional types (SBFT), defined on the basis of singularities of their persistence in soil, be identified in the Festuca pallescens grasslands? (b) Do different above-ground vegetation states modify the expression of SBFT singularities? (c) Is the potential for vegetation recovery from the soil seed bank associated with the characteristics of their SBFT? To address these questions we examined the sizes of immediately and non-immediately-germinable seed banks (IGSB and NIGSB, respectively) in four different vegetation states of the steppe of F. pallescens resulting from the combined effects of topography and grazing. The results show that four lifeforms (perennial grasses, perennial graminoid non-grasses, annual dicots and annual grasses) display three characteristic SBFT. These are: (1) a transient type constituted by perennial grasses (SBFT1), (2) an intermediate type represented by annuals (SBFT2), and (3) a persistent type characteristic of one perennial graminoid non-grass (SBFT3). Other lifeforms (perennial dicots and biennials) could not be assigned to any of these types or characterized into a definite one. Seed bank functional types do not change among vegetation states in terms of the relative proportions of IGSB and NIGSB, although differences in the absolute and the relative size of each SBFT could be found. Species with persistent or mixed persistent/non-persistent seed bank types (SBFT2, SBFT3, etc.) colonize habitats disturbed by grazing with more success than those with non-persistent seed banks (SBFT1). Species with persistent seed banks are over-represented in the soil seed bank in relation to their contribution to above-ground cover. Management strategies for conservation in these grasslands could conveniently be targeted to increase the seed rain of perennial grasses as well as to the creation of suitable micro-environmental conditions to enhance their establishment.     

地中海沿岸沙丘土壤种子库的异质性

应用自然萌发法和物理筛选法相结合的方法,调查了地中海沿岸沙丘三种微生境土壤总种子库和永久种子库特征,用功能群的方法分析了微生境之间的土壤总种子库和永久土壤种子库的组成和结构差异,也分析了主要物种土壤种子库的微生境分布格局,分析了种子大小和土壤种子库中的种子永久性关系。发现地中海沿岸沙丘土壤种子库具有明显的空间异质性,即使在相同的微生境内,土壤种子库的分布也不是均匀的,甚至具有很大的差异;微生境对总的土壤种子库和各功能群的土壤种子库的分布格局具有显著的影响,开阔地区域具有最大的种子密度,而灌丛下和路径具有较小的种子密度;在永久土壤种子库中,豆科类植物种子在休眠种子中占有最大的比例,约为76％,而一年生和多年生禾草未发现休眠种子,豆类、伞形科类、多年生阔草、菊科类、一年生阔叶草和十字花科类等种子在土壤中的永久性比例依次下降,分别为50％、46％、41％、6％、6％和1％,微生境影响各功能群种子在土壤中的永久性。微生境显著影响大部分主要物种的土壤种子库分布;种子大小与其在土壤中的永久性为正相关,即大种子具有较高的永久性,小种子具有较低的永久性。     

Depth distribution and composition of seed‐banks in alien‐invaded and uninvaded fynbos vegetation

South African fynbos vegetation is threatened on a large scale by invasive woody plants. A major task facing nature conservation managers is to restore invaded areas. The aim of this study was to determine the restoration potential of fynbos following dense invasion by the Australian tree Acacia saligna. The impacts of dense invasion on seed‐bank composition and depth distribution were investigated to determine which fynbos guilds and species have the most persistent seed‐banks. Soil samples were excavated at three different depths for invaded and uninvaded vegetation at two sand plain and mountain fynbos sites. Seed‐banks were determined using the seedling emergence approach. Invasion caused a significant reduction in seed‐bank density and richness at all sites. There was a significant, but smaller, reduction in seed‐bank density and richness with soil depth at three sites. Seed‐bank composition and guild structure changed following invasion. Low persistence of long‐lived obligate seeders in sand plain fynbos seed‐banks indicates that this vegetation type will be difficult to restore from the seed‐bank alone following alien clearance. The dominance of short‐lived species, especially graminoids, forbs and ephemeral geophytes, suggests that regenerating vegetation will develop into a herbland rather than a shrubland. It is recommended that seed collecting and sowing form part of the restoration plan for densely invaded sand plain sites. As seed density remained higher towards the soil surface following invasion, there is no general advantage in applying a mechanical soil disturbance treatment. However, if the shallow soil seed‐bank becomes depleted, for example following a hot fire through dense alien slash, a soil disturbance treatment should be given to exhume the deeper viable seed‐bank and promote recruitment.     

土壤种子库研究综述

土壤种子库是指存在于土壤表面和土壤中全部存活种子的总和。土壤种子库研究是植物生态学研究的一个重要领域。研究土壤种子库是对生物多样性研究的一个重要补充 ,有助于对植被更新和植被演替动态的了解 ,对于植被重建与恢复具有指导意义 ,有利于指导我们的生产实践。本文从土壤种子库研究的取样方法、研究内容及进展等方面进行一个较系统的总结 ,为将来的研究提供一些有益的途径。     

Linking the pattern to the mechanism: How an introduced mammal facilitates plant invasions

Non‐native mammals that are disturbance agents can promote non‐native plant invasions, but to date there is scant evidence on the mechanisms behind this pattern. We used wild boar (Sus scrofa) as a model species to evaluate the role of non‐native mammals in promoting plant invasion by identifying the degree to which soil disturbance and endozoochorous seed dispersal drive plant invasions. To test if soil disturbance promotes plant invasion, we conducted an exclosure experiment in which we recorded emergence, establishment and biomass of seedlings of seven non‐native plant species planted in no‐rooting, boar‐rooting and artificial rooting patches in Patagonia, Argentina. To examine the role of boar in dispersing seeds we germinated viable seeds from 181 boar droppings and compared this collection to the soil seed bank by collecting a soil sample adjacent to each dropping. We found that both establishment and biomass of non‐native seedlings in boar‐rooting patches were double those in no‐rooting patches. Values in artificial rooting patches were intermediate between those in boar‐rooting and no‐rooting treatments. By contrast, we found that the proportion of non‐native seedlings in the soil samples was double that in the droppings, and over 80% of the germinated seeds were native species in both samples. Lastly, an effect size test showed that soil disturbance by wild boar rather than endozoochorous dispersal facilitates plant invasions. These results have implications for both the native and introduced ranges of wild boar, where rooting disturbance may facilitate community composition shifts.     

Resilience of soil seed banks to site degradation in intermittently flooded riverine woodlands

Questions: (1) What is the recovery potential of soil seed banks of intact, average and degraded floodplain woodlands? (2) Will soil seed banks of different functional groups (native and exotic, dryland and wetland) display contrasting responses to site degradation? Location: Semi‐arid, seasonally flooded woodland of eastern Australia. Methods: Diversity, abundance and composition of soil seed banks were assessed using a glasshouse study. Surface soil samples were taken from a total of nine sites with three levels of degradation (intact, average, degraded) from three microsites (sub‐canopy, canopy edge, open). Results: A total of 26 662 individuals of 82 species germinated. Seed abundance increased tenfold from intact to degraded sites, but there was no effect on richness. Species composition of all functional groups varied significantly among degradation states. Seeds of native wetland and exotic dryland species were more abundant in degraded than in intact sites. However, the abundance of native dryland germinants did not differ among degradation classes and no seeds of exotic wetland species were observed. Richness of exotic dryland species was significantly higher in degraded sites. Conclusions: Increasing disturbance promoted seed banks of exotic but not native dryland species and native but not exotic wetland species. Unexpectedly, disturbance promoted the abundance of native seeds more than exotics, although this was driven by a single species. Our results suggest that the dryland phase of the floodplain community is more resilient to degradation than predicted.     

Edaphic patchiness influences grassland regeneration from the soil seed‐bank in mountain grasslands of central Argentina

The soil seed‐banks in the main natural vegetation patches that make up mountain grasslands on granite substrates in central Argentina were studied. The main natural vegetation types are moist swards, tall‐tussock grasslands and stony grasslands. Ten compound soil samples from each community at two soil depths (0–5 and 5–10 cm) were taken. The density of soil seed‐banks was highest in moist swards, intermediate in stony grasslands and lowest in tall‐tussock grasslands. Low levels of similarity were found between the established vegetation and total soil seed‐bank in tall‐tussock grasslands and stony grasslands, but the similarity was higher in swards. In all three communities the seed‐bank was most frequently transient in nature. Short‐term persistent and long‐term persistent seed‐banks were less frequent. Regeneration from the seed‐banks after disturbance is expected to differ among communities on different edaphic patches. On the basis of the density and longevity of the soil seed‐banks and the similarity to the established vegetation, potential for in situ regeneration should be lower in tall‐tussock grasslands, intermediate in stony grasslands and higher in moist swards.     

Non‐native conditions favor non‐native populations of invasive plant: demographic consequences of seed size variation?

Trait differences between native and non‐native populations may explain the greater abundance and impact of some organisms in their non‐native ranges than in their native ranges. Here, we conducted reciprocal common gardens in southwestern Turkey (home) and central Argentina (away) to explore the hypothesis that the greater success of the invasive ruderal Centaurea solstitialis in Argentina than Turkey is partially explained by differences between home and away populations. Unusual among common gardens, our experimental design included seed additions to explicitly evaluate population level responses, as well as disturbance and no‐disturbance treatments. We documented seed mass in native and non‐native populations, and during the experiment, we periodically measured density, plant size, and herbivory. After six months, we determined the establishment of plants for populations from both origins in both home and away common gardens. Seed mass was two times larger for Argentinean than Turkish populations. Density, plant size and final establishment were also greater for plants from Argentinean than from Turkish populations, but only in the common garden in Argentina. In Turkey, no differences between population origins were detected for these variables. Herbivory was similar for populations from both origins in both common gardens. As expected, disturbance generally increased plant performance in both regions. Our results suggest that increased seed size in non‐native populations may have demographic consequences under non‐native conditions that can contribute to the invasive success of C. solstitialis. This is the first reciprocal common garden that supports the idea that seed size variation contributes to demographic differences for an invasive species between native and non‐native distributions, but our findings further suggest that seed size effects on demography depend on the ecological context in which population processes occur.     

Modeling and Analysis of a Density-Dependent Stochastic Integral Projection Model for a Disturbance Specialist Plant and Its Seed Bank

In many plant species dormant seeds can persist in the soil for one to several years. The formation of these seed banks is especially important for disturbance specialist plants, as seeds of these species germinate only in disturbed soil. Seed movement caused by disturbances affects the survival and germination probability of seeds in the seed bank, which subsequently affect population dynamics. In this paper, we develop a stochastic integral projection model for a general disturbance specialist plant-seed bank population that takes into account both the frequency and intensity of random disturbances, as well as vertical seed movement and density-dependent seedling establishment. We show that the probability measures associated with the plant-seed bank population converge weakly to a unique measure, independent of initial population. We also show that the population either persists with probability one or goes extinct with probability one, and provides a sharp criteria for this dichotomy. We apply our results to an example motivated by wild sunflower (Helianthus annuus) populations, and explore how the presence or absence of a “storage effect” impacts how a population responds to different disturbance scenarios.     

The coupling of recruitment and disturbance by fire in two resprouting Proteaceae species

Recruitment in plant populations is often tightly coupled to major disturbances such as fires. For species with persistent seed banks, fire-related cues may allow or enhance germination. The litter layer influences germination and may modify the impact of seed predators on seeds and seedlings. The litter layer is obviously affected by fire, providing one mechanism by which disturbance can determine recruitment. We tested the role of litter in the disturbance–recruitment coupling of two species with contrasting seed release timing after fire—Banksia serrata (canopy seed bank) and Telopea speciosissima (transient seed bank) by planting their seeds both early and late in the post-fire recruitment period (PRP) and manipulating litter density in orthogonal treatments. Vertebrate seed predators were excluded. Both species established more seedlings late in the PRP, although results were strongly influenced by very poor establishment at one site. Invertebrate seed predators consumed more T. speciosissima seeds in sites early (69.5%) than late in the PRP (51.2%), while consumption of B. serrata seeds was lower overall and comparable across sites (average 47.3%). Surprisingly, litter had very little effect on establishment and none on invertebrate seed predation, suggesting that other factors are more important. Recruitment was only loosely coupled to disturbance for the canopy seed bank species; for the transient seed bank species, the coupling was tighter but separated in time from the disturbance. Understanding both the strength and temporal aspects of the disturbance–recruitment coupling is necessary for appropriate management of plant functional diversity in fire-prone habitats.     

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.     

Dispersal and microsite limitation in Australian old fields

The recovery of native communities after cultivation may be constrained by (a) the failure of species to reach a site or (b) their failure to survive once there. Although seed addition is a common method to test for seed versus microsite limitation, most studies do not follow populations beyond seedling establishment, nor do they measure seed dispersal. We examined dispersal across native grassland/old field boundaries and investigated the relative importance of seed and microsite limitation across multiple life-history stages and generations. Seed trapping showed little movement of native seeds into old fields and that most species had extremely localized dispersal. Consequently, there was no pattern of seed density with distance from boundaries, and similarity between the seed rain and standing vegetation was moderate to high. Seed addition showed that two annual species were able to establish in all, and flower in most, subplots in the first year, and that seedling establishment increased with sowing density, consistent with seed limitation. However, the relative importance of microsite limitation increased over the lifespans of the species. Density dependence reduced the number of flowering plants, resulting in a large decline in seedling density in the following generation. This decline continued so that the initial positive effect of sowing density on seedling numbers disappeared by the fourth generation and hence the persistence of populations is uncertain. Thus, by monitoring seed dispersal and following experimental populations beyond seedling establishment, we showed that dispersal limits species distributions, but microsite plays an important role in limiting population growth and persistence.     

Patterns of seed persistence in South African fynbos

In fire-prone communities such as fynbos, many species rely on regeneration from seed banks in the soil. Persistent seed banks are particularly important for species with life spans shorter than the average fire cycle, in order to counter local extinction. Persistent seed banks also give potential for restoring ecosystems following disturbances such as alien plant invasion. This study investigated the seed persistence patterns of 25 perennial species, representing several growth forms and life histories, during a three-year burial. Long-term persistence (i.e., seed bank half-life exceeding two years) was found in the hard-seeded Fabaceae and Pelargonium, and the nut-fruited Proteaceae. In this group, germinability was low and dormancy increased further following burial, resulting in a highly viable, dormant seed bank after three-year's burial. A second group with potentially long-term persistent seeds includes four taxa (Pseudopentameris, Passerina, Elegia and Restio) that either have low germinability or develop secondary dormancy following burial. Dormancy in the latter group was partially countered by exposure to smoke-seed primer. Of the small-seeded species, only two Erica species with high initial dormancy had long-term persistent seed banks. The other species mostly displayed high initial germinability and short-term persistent seed banks (i.e., seed bank half-life less than two years). This group included taxa with short to medium life-spans (Syncarpha, Roella) that were expected to have long-term persistent seeds in order to buffer against local extinction following average to long fire-return intervals. We hypothesize that light may play a role in overcoming secondary dormancy in those species, and could have resulted in an underestimate for seed persistence in this study. Alternatively, those short to medium life-span species persist via inter-fire recruitment in gaps or long-distance dispersal (of the smallest seed). No correlations were found between seed persistence and seed mass or variance in seed dimensions. Nor was a correlation found between seed persistence and phenol concentration. In fynbos, seed burial of larger seeds by ants and rodents are major processes that operate in conjunction with passive burial of small seeds. Selection for persistence can be expected to operate across all seed sizes and shapes in fire-prone communities.     

Methodological bias in the seed bank flora holds significant implications for understanding seed bank community functions

• Persistent seed banks are a key plant regeneration strategy, buffering environmental variation to allow population and species persistence. Understanding seed bank functioning within herb layer dynamics is therefore important. However, rather than assessing emergence from the seed bank in herb layer gaps, most studies evaluate the seed bank functioning via a greenhouse census. We hypothesise that greenhouse data may not reflect seed bank‐driven emergence in disturbance gaps due to methodological differences. Failure in detecting (specialist) species may then introduce methodological bias into the ecological interpretation of seed bank functions using greenhouse data.
• The persistent seed bank was surveyed in 40 semi‐natural grassland plots across a fragmented landscape, quantifying seedling emergence in both the greenhouse and in disturbance gaps. Given the suspected interpretational bias, we tested whether each census uncovers similar seed bank responses to fragmentation.
• Seed bank characteristics were similar between censuses. Census type affected seed bank composition, with >25% of species retrieved better by either census type, dependent on functional traits including seed longevity, production and size. Habitat specialists emerged more in disturbance gaps than in the greenhouse, while the opposite was true for ruderal species. Both censuses uncovered fragmentation‐induced seed bank patterns.
• Low surface area sampling, larger depth of sampling and germination conditions cause underrepresentation of the habitat‐specialised part of the persistent seed bank flora during greenhouse censuses. Methodological bias introduced in the recorded seed bank data may consequently have significant implications for the ecological interpretation of seed bank community functions based on greenhouse data.

     

Seed dormancy and hybridization effect of the invasive species,Helianthus annuus

Helianthus annuus is an invasive alien species naturalised in the central region of Argentina where it shares an extended area with the sunflower crop. As this species has also invaded several other sunflower crop growing areas in the world, it severely restricts the use of new technologies, for example herbicide tolerance by genetic modification. The natural seed dormancy of the wild Helianthus strains from the centre of origin in North America is well known, but the seed dormancy of the invasive biotypes is still unknown. Dormancy is a fitness trait related to the establishment, dispersion and persistence of invasive weeds. Four experiments were designed to investigate the effect of the pericarp, light, temperature, the after‐ripening period and hybridization with the DK3880CL sunflower crop (F1) on the seed dormancy of five invasive H. annuus biotypes. The results showed that pericarp scarification increased imbibition of the whole achene by 19%. Light stimulation only increased germination in the wild biotype without any effect on the domesticated sunflower. A period of 12 months after‐ripening at 5°C reduced seed dormancy in the wild biotype and its progeny; the optimal temperature for seed germination at this period was found to be 15°C. Mechanical scarification was the best treatment for overcoming seed dormancy with a differential germination, in the biotypes with the highest response, superior to 63%. Hybridization with domesticated sunflower had a minimal or no effect on seed dormancy but the germination rate was improved in three F1 crosses. Wild biotype dormancy appears to be governed by the maternal pericarp and intrinsic hormone regulation. An increased germination rate of some progenies could constitute an advantage during seedling establishment but only in winters without any frost.