Comparison of two methods characterising the seed bank of amphibious plants in submerged sediments

We analysed the submerged soil seed bank of three fishponds in the Waldviertel region in Austria. We aimed our study at comparing the efficiency of two methods in detecting seeds quantitatively from soil samples of four characteristic mud-flat species, i.e. Carex bohemica, Coleanthus subtilis, Elatine hexandra, and Eleocharis ovata: the seedling-emergence and the rinsing method. Additionally, the actual vegetation was described based on 65 phytosociological relevés. Soil seed bank analyses were based on 31 samples representing the vegetation zonation. Mixed soil samples were portioned into 62 subsamples further treated with the two methods in parallel.     

桂西南石漠化山地土壤种子库的基本特征及植被恢复对策

采用幼苗萌发法对广西平果县龙何示范区石漠化山地的土壤种子库进行初步研究。结果表明,该地区土壤种子库共有108种植物,隶属于33科81属,其中草本81种、灌木20种、藤本7种;其土壤种子库的种子密度为64.6~339.7粒.m-2,且在不同土地利用类型区及不同季节存在较大差别。在分析土壤种子库对其植被恢复作用的基础上,认为可采取自然封育和人工造林等措施,以促进现存植被的正向演替。     

秦岭北坡不同生境栓皮栎种子雨和土壤种子库动态

为了阐明栓皮栎种子雨和种子库动态,以秦岭北坡林下、林窗、林缘3种生境栓皮栎天然林为对象,采用离地和地面收集种子的方法,连续定位观测了栓皮栎种子雨、种子库的数量、质量动态,以及幼苗发育过程.结果表明:栓皮栎种子雨从8月中旬开始,9月中旬到10月上旬达到高峰期,11月上旬结束;3种生境种子雨降落历程、发生时间和组成不同;林下种子雨强度最大,为(39.55±5.56)粒·m-2,林窗种子雨降落时间最早,持续时间最长,种子活力最高,而林缘成熟种子占其种子雨的比例最大,达58.7％.从种子雨降落结束到翌年8月,土壤种子库总储量均以林下最大,林缘最小;各生境的土壤种子库中成熟、未成熟、被啃食种子数量和种子活力均随时间变化呈递减趋势,而霉烂种子数量则相反.各生境的土壤种子库中的种子均主要集中在枯落物层,其次为0～2 cm土层,2～5 cm土层中只有极少量种子存在.3种生境中栓皮栎幼苗的密度差异显著,林窗幼苗最多,林缘次之,林下最少.说明林窗更适合栓皮栎种子的萌发和幼苗生长.在栓皮栎林的经营中,通过适当间伐、增加林窗数量,可以促进栓皮栎林的天然更新.     

Germinable soil seed banks of anthropogenic native grasslands and grassy forest remnants in temperate south-eastern Australia

Soil seed banks of anthropogenic native grassland and grassy forest remnants on the Gippsland Plain in south-eastern Australia were studied using the seedling emergence method. Intact examples of both ecosystems are rare, owing to extensive agricultural development. Both ecosystems are assumed to have been derived since European settlement from the same original, grassy forest ecosystem. It was hypothesised that species now restricted to grassland remnants might persist in the soil seed bank of forest remnants, and vice versa. This hypothesis was not supported. In total, 25554 seedlings of at least 155 species emerged from forest and grassland seed banks collectively. Small-seeded, annual and perennial herbs were most abundant. Forest seedbanks differed substantially in composition from grassland seedbanks, and both essentially contained a subset of the species in the vegetation. Forest seedbanks contained significantly more species and individuals of annual and perennial native dicotyledons than grassland seedbanks. Seedbanks made a major contribution to local diversity, since many species in the seed bank at each quadrat were not recorded from the vegetation, but only a minor contribution to regional diversity. Species in the seedbank that were absent from all vegetation samples were recorded at few quadrats, except Juncus species, which were widespread and abundant in the seedbank. The apparent absence from forest seed banks of species that are best represented in grassland remnants (and vice versa), suggests that there is little opportunity of recruiting grassland-restricted species in forest remnants by instigating grassland management practices.     

Seed vigor and plant competitiveness resulting from seeds of Eupatorium adenophorum in a persistent soil seed bank

Seeds in a persistent soil seed bank (PSSB) provide an effective way to maintain plant population and community stability. Seeds that persist in soil incur physiological costs of maintaining viability and vigor, thus, the growth capability of resulting plants may be reduced. However, a lot of functional roles of the PSSB have been deduced from seed germination capability, and little consideration has been given to interspecific and intraspecific competitive ability of the resulting plants. Eupatorium adenophorum was used as the study species to compare germination of different artificially aged PSSB seeds and competition at different densities between resulting plants of aged and freshly produced seeds. Seed burial caused decreases in survival rates but not germination speed. During the 175-day growth period, the individual biomass, average height, basal stem diameter and leaf number of plants from aged PSSB seeds were little lower than that of plants germinated from freshly produced seeds. However, the differences were not significant at any densities. Thus, (1) although seeds stored in soil exhibited a very high death rate, they maintained a high vigor for germination, and (2) resulting plants from PSSB seeds exhibited good competiveness to plants from new seeds of the same population. The results further confirm the significance of PSSB in maintaining stability of plant populations and communities.     

辽东山区长白落叶松(Larix olgensis)种子雨和种子库

长白落叶松是东北地区主要的用材树种,其种子雨和种子库研究鲜见报道。在辽东山区用收集器收集的种子分析了长白落叶松种子雨组成、质量和扩散距离,每隔2个月调查1次种子库数量,并结合靛蓝染色法测定每次种子的活力来分析土壤种子库动态。结果表明,辽东山区的长白落叶松种子雨从8月中旬开始,9月末到10月初达到高峰期,11月初结束。在起始期,种子雨以干瘪的不完整种子为主,而从高峰期开始,种子雨以完整种子为主。整个长白落叶松种子雨中不完整种子约占种子雨总量的45％,这些不完整种子由被动物取食、空粒和病虫害危害种子组成。完整种子的平均生活力为56．4％,即有活力的种子仅占整个种子雨的30％。种子雨集中在母树周围,在林缘1次扩散距离一般不超过1．5倍树高。种子雨到达地面之后,主要分布在枯枝落叶层,土壤0—5em层有少量分布,土壤5em以下没有种子分布;土壤种子库的种子主要在翌年雪融化后开始萌发、被取食、搬运以及腐烂,其中腐烂种子数占45．4％,动物取食为30．0％。种子库的种子数量和活力在冬季没有明显变化,而在翌年,种子数量和活力明显减少,4、6月和8月份种子数量分别为（506．3±35．56）粒m^-2,（267．1±17．47）粒m^-2和（143．6±9．83）粒m^-2,对应的活力分别为47．8％±4．68％,19．4％±3．39％和0％,这表明长白落叶松种子不能在地面形成连续的种子库。     

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.     

Safe sites for establishment of Nymphoides peltata seedlings for recovering the population from the soil seed bank

The population of the endangered plant species Nymphoides peltata in Lake Kasumigaura, Japan, has been declining drastically recently, and seedlings that emerge from the remaining soil seed bank have entirely failed to establish. The decline has followed artificial control of the water level in the lake. To examine the environmental requirements at the seedling establishment stage, we investigated the survival and growth of emerged seedlings at various microsites on the lakeshore by manipulating environmental conditions such as exposure to waves, inundation, and light availability so as to include the conditions of the presumed safe sites. Seedling survival at the early stage was affected most by environmental variables relating to the susceptibility to inundation. Survival until seedling establishment was profoundly affected by light availability as well as by susceptibility to inundation. In all, 136 genets were established in quadrats less prone to inundation and with sufficient light availability, which is consistent with the presumed safe-site characteristics of the original water regime: bare ground exposed during the spring water-level drawdown. Recovering the original water regime with seasonal drawdown will be indispensable for recovering a self-sustainable population. However, as first-aid measures, active restoration efforts through adaptive management using the remnant soil seed bank are urgently needed before the soil seed bank becomes exhausted.     

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.     

中国矿区土壤种子库研究的必要性与挑战

土壤种子库是土壤及其表面凋落物中所有具生命活力的种子,可反映区域特有的生物多样性特征,其多数存在于表层土壤.作为植被恢复生长的基础和潜在的绿化材料,表土和土壤种子库是矿区不可再生的有限资源.土壤种子库研究是我国矿区土地复垦与生态重建领域的热点之一.由于矿业生产的特殊性,矿区土壤种子库研究不能仅仅关注土壤种子库中种子类型、数量及其与地表植被相互关系等常规静态内容,还需要借鉴特殊生境下土壤种子库的研究成果,并结合矿区土地利用特征,在研究体系和思路上寻求突破.本文总结了矿区土壤种子库研究的特殊性及相关研究进展,综述了特殊生境下土壤种子库的研究进展及启示,并提出了我国矿区土壤种子库研究所面临的挑战,为强化我国矿区土壤种子库研究、提高我国矿区土地复垦中表土及土壤种子库利用效率、加快植被恢复进程提供参考.     

Relationship between seed bank expression, adult longevity and aridity in species of Chaetanthera (Asteraceae) in central Chile

BACKGROUND AND AIMS: Broad surveys have detected inverse relationships between seed and adult longevity and between seed size and adult longevity. However, low and unpredictable precipitation is also associated with seed bank (SB) expression in semi-arid and arid areas. The relationship between adult longevity, SB formation, seed mass and aridity is examined in annual and perennial herbs of Chaetanthera (Asteraceae) from the Chilean Mediterranean-type climate and winter-rainfall desert areas over a precipitation range of one order of magnitude. METHODS: Seeds of 18 species and subtaxa (32 populations) were buried in field locations, and exhumed after two successive germination periods. Seeds not germinating in the field were tested in a growth chamber, and remnant intact seed tested for viability. Seed banks were classed as transient or persistent. The effect of life form, species, population and burial time on persistent SB size was assessed with factorial ANOVA. Persistent seed bank size was compared with the Martonne aridity index (shown to be a surrogate for inter-annual variation in precipitation) and seed size using linear regression. ANCOVA assessed the effect of life-form on SB size with aridity as covariate. KEY RESULTS: Three species had a transient SB and 15 a persistent SB. ANOVA revealed a significant effect of life-form on SB size with annuals having larger SB size and greater capacity to form a persistent SB than perennials. Significant inter-population variation in SB size was found in 64% of cases. Seed mass was negatively correlated with persistent SB size. Persistent seed bank size was significantly correlated with the Martonne aridity index in the perennial and annual species, with species from more arid areas having larger persistent SBs. However, when aridity was considered as a covariate, ANCOVA revealed no significant differences between the annual and perennial herbs. CONCLUSIONS: Persistent seed bank size in Chaetanthera appears to reflect environmental selection rather than any trade-off with adult longevity.     

Persistent soil seed banks and floristic diversity in Fagus orientalis forest communities in the Hyrcanian vegetation region of Iran

We assessed the size of seed bank, species diversity and similarity between seed bank and standing vegetation in four oriental beech (Fagus orientalis Lipsky) community types of the central Hyrcanian forests of northern Iran. For this purpose a total of 52 relevés was established in two associations and two subassociations of the beech forests, and six soil samples (20 × 20 cm square and to a depth of 10 cm) were collected in each relevé in mid-spring, after the germination season had ended. Soil seed bank was investigated using the seedling emergence method. A total of 63 species, 57 genera and 36 families was represented in the persistent soil seed bank of the forest communities. The seed bank contained 28 species not found as adult plants in the vegetation, but these were mostly early successional species. Size of the seed bank ranged from 3740 to 4676 individuals m⁻² in the Rusco hyrcani-Fagetum orientalis and Danae racemosae-Fagetum orientalis associations, respectively. Species composition of seed banks and aboveground vegetation had low similarity with an average of 24.3% in the four plant communities, because only 38% of the species were the same in the vegetation and the seed banks. Most seeds in the seed bank were from early successional species, and the only tree with a large persistent seed bank was the fast-growing pioneer Alnus subcordata. DCA ordination also demonstrated low similarity between soil seed bank and vegetation. The soil seed banks of the four beech communities did not differ significantly in size, composition, diversity and uniformity. Although above ground vegetation in the four community types is floristically distinct, there is considerable overlap among the soil seed banks because they contain in a similar way early successional species. Further, the absence of typical forest species in the soil seed bank indicates that restoration of forest tree species cannot rely on the soil seed bank.     

Seasonal variation in seed bank composition and its interaction with nutrient enrichment in the Everglades wetlands

In the Florida Everglades, nutrient enrichment from agricultural outflow and the change in hydrology have collectively contributed to the expansion of cattails (Typha spp.). To assess the effectiveness of prescribed fire in controlling cattails and to predict vegetation dynamics after the fire, it is important to understand the seasonal variation of the soil seed bank and how the seed bank is affected by nutrient enrichment and fire. This paper investigates the effects of season, nutrient enrichment, and fire on soil seed bank species composition, richness, and density along a nutrient gradient in Water Conservation Area 2A (WCA 2A) of the Florida Everglades. Species richness was significantly affected by nutrient enrichment and season but not their interaction. Total seed density, however, was significantly affected by the interaction between nutrient enrichment and season. Yet, at species level, the relationship between seed density, nutrient enrichment and season varied. The highest seed density of cattail occurred in summer at highly enriched sites, but that of sawgrass occurred in fall regardless of enrichment; the seed density of water lily was very low regardless of season and nutrient enrichment, and the highest Amarathus seed density occurred at highly enriched sites year round. Moreover, germination timing differed greatly among species. While cattail seeds had a short incubation period and started to germinate 2–3 days after initiation of the germination assay, sawgrass seeds generally started to germinate 4 weeks later. Further, both the prescribed summer fire at the highly enriched site and the natural winter fire at the moderately enriched site reduced the seed density of cattail but not of sawgrass. Our results suggest that fire application for vegetation recovery in WCA 2A would benefit from explicitly considering seasonal dynamics of the seed bank.     

Germination traits explain soil seed persistence across species: the case of Mediterranean annual plants in cereal fields

Background and Aims

Seed persistence in the soil under field conditions is an important issue for the maintenance of local plant populations and the restoration of plant communities, increasingly so in the light of rapidly changing land use and climate change. Whereas processes important for dispersal in space are well known, knowledge of processes governing dispersal in time is still limited. Data for morphological seed traits such as size have given contradictory results for prediction of soil seed persistence or cover only a few species. There have been few experimental studies on the role of germination traits in determining soil seed persistence, while none has studied their predictive value consistently across species. Delayed germination, as well as light requirements for germination, have been suggested to contribute to the formation of persistent seed banks. Moreover, diurnally fluctuating temperatures can influence the timing of germination and are therefore linked to seed bank persistence.

Methods

The role of germination speed measured by T₅₀ (days to germination of 50 % of all germinated seeds), light requirement and reaction to diurnally fluctuating temperatures in determining seed persistence in the soil was evaluated using an experimental comparative data set of 25 annual cereal weed species.

Key Results

It is shown that light requirements and slow germination are important features to maintain seeds ungerminated just after entering the soil, and hence influence survival of seeds in the soil. However, the detection of low diurnally fluctuating temperatures enhances soil seed bank persistence by limiting germination. Our data further suggest that the effect of diurnally fluctuating temperatures, as measured on seeds after dispersal and dry storage, is increasingly important to prevent fatal germination after longer burial periods.

Conclusions

These results underline the functional role of delayed germination and light for survival of seeds in the soil and hence their importance for shaping the first part of the seed decay curve. Our analyses highlight the detection of diurnally fluctuating temperatures as a third mechanism to achieve higher soil seed persistence after burial which interacts strongly with season. We therefore advocate focusing future research on mechanisms that favour soil seed persistence after longer burial times and moving from studies of morphological features to exploration of germination traits such as reaction to diurnally fluctuating temperatures.     

Aerial and soil seed banks enable populations of an annual species to cope with an unpredictable dune ecosystem

Background and Aims

Simultaneous formation of aerial and soil seed banks by a species provides a mechanism for population maintenance in unpredictable environments. Eolian activity greatly affects growth and regeneration of plants in a sand dune system, but we know little about the difference in the contributions of these two seed banks to population dynamics in sand dunes.

Methods

Seed release, germination, seedling emergence and survival of a desert annual, Agriophyllum squarrosum (Chenopodiaceae), inhabiting the Ordos Sandland in China, were determined in order to explore the different functions of the aerial and soil seed banks.

Key Results

The size of the aerial seed bank was higher than that of the soil seed bank throughout the growing season. Seed release was positively related to wind velocity. Compared with the soil seed bank, seed germination from the aerial seed bank was lower at low temperature (5/15 °C night/day) but higher in the light. Seedling emergence from the soil seed bank was earlier than that from the aerial seed bank. Early-emerged (15 April–15 May) seedlings died due to frost, but seedlings that emerged during the following months survived to reproduce successfully.

Conclusions

The timing of seed release and different germination behaviour resulted in a temporal heterogeneity of seedling emergence and establishment between the two seed banks. The study suggests that a bet-hedging strategy for the two seed banks enables A. squarrosum populations to cope successfully with the unpredictable desert environment.     

Seed bank versus seed rain in the regeneration of a tropical pioneer tree

Summary We used the tropical pioneer tree, Cecropia obtusifolia to evaluate the relative importance of different sources of seeds in the regeneration of species that depend on ephemeral sites. We studied seed production in a population established in a 5 ha plot, and dispersal, dormancy and seed predation in two recent treefall gaps (<1 year-old), two building or successional forest patches (10–15 since disturbed), and two mature forest patches (>35 years since disturbed) for a one year period at Los Tuxtlas (Mexico). Flowers and fruits were counted at monthly intervals. Annual fecundity per tree ranged from 1.4×10⁴ to 1.4×10⁷ seeds. Seeds were continuously available on the trees and on the ground. Average annual seed rain per m² (as measured by 0.5×0.5 m seed traps) varied from 184 to 1925 among the six sites. Distance to nearest seed source and patch type explained more than 60% of the seed rain variation among sites. Soil seed density, estimated by counting seeds from ten samples (78.5 cm²×10 cm deep) collected from each site in October and January, ranged among the six sites from 269 to 4485 seeds per m² in January and from 204 to 5073 in October. Soil seed viabilities were much lower (17.1% in October and 5.1% in January) than those of rain seeds (48.26%). Annual survivorships of 2.2% were estimated for seeds artificially sown on the soil surface of a gap and a mature patch, and 3.75% in a building patch. In two other experiments seed removal rates ranged from 27% to 98% in 4 days. Removal rates were significantly higher in gap and mature patches than in building patches. Ants (Paratrechina vividula) and grasshopper nymphs (Hygronemobius. sp.) were the main predators. We draw three main conclusions from our data: (1) Pathogens and predators determine low survivorship of C. obtusifolia's seeds in the soil and a rapid turnover rate (1.07 to 1.02 years) of its seed bank; (2) a continuous and copious seed production and an abundant and extensive seed rain replenish the soil seed pool in patches with different disturbance ages at least up to 86 m from nearest source; (3) more than 90% of the seeds contributing to C. obtusifolia seedling recruitment in gaps are less than one year-old. We discuss our results in the context of previous similar studies for tropical forests.     

Comparison between the soil seed banks of a burnt and an unburnt Quercus pyrenaica Willd. forest

Soil samples from burnt and unburnt sites dominated by Quercus pyrenaica Willd. forest in León province (NW Spain) were collected, separated into an upper layer (0–2 cm depth) from a lower layer (2–5 cm), put in a greenhouse, and seeds allowed to germinate.A total of 670 identified seedlings comprising 56 species and belonging to 24 families were recorded. Most seedling were herbaceous perennials (hemicryptophytes: 59%), followed by annuals (therophytes: 23%). Many species that germinated from buried seeds were not observed as plants at any site, and came from exogenous communities. The principal means of seed dissemination were anemochory (45%) and autochory (23%).The number of species as well as seedlings was not significantly different between soils from the burnt and unburnt sites, but seedlings were more numerous in samples from the unburnt sites, as the number of seedlings was always highest in the upper soil layer. Germination behaviour of four particular species was characterized.Seedlings from the seed bank temporarily were found in the early stages of recovery of the burnt Quercus pyrenaica forests.     

Red crabs in rainforest on Christmas Island,Indian Ocean: No effect on the soil seed bank

Red land crabs (Gecarcoidea natalis) are both abundant and widespread in intact rainforest on Christmas Island, Indian Ocean, occurring at densities of ~ 1 crab m^–2. We used an on-going exclusion experiment to test the hypothesis that through their activities as seed predators and soil disturbers, these omnivores are important determinants of the density and relative species abundance of seeds in the soil seed bank of undisturbed primary rainforest. After 6.5 y of continuous crab exclusion, there was no significant difference in the density of seeds in the top 3 cm of soil between the control (3671 ± 517 seeds/0.19 m²) and exclusion plots (3285 ± 801 seeds/0.19 m²), nor was there any significant treatment difference in relative species composition. There were also no significant treatment differences when Muntingia calabura, which accounted for 91.9% of all seeds in the seed bank, was excluded from the analyses. We attribute the lack of a significant impact of red crabs to their probable inability to handle the very small seeds which occurred in the seed bank, and the low level of soil disturbance at the study site. We conclude that the observed impact of red crabs on the abundance and diversity of successional species in natural light gaps on Christmas Island is due to their impact on germinating seedlings alone, rather than any additional impact on the soil seed bank.     

Impact of ploughing on soil seed bank dynamics in temporary pools

We examined the impact of ploughing on soil seed banks of plant communities living in temporary marshes located in agricultural fields. The quantity, quality and vertical distribution of seeds were quantified under ploughed or unploughed treatment at community level. We also focussed on a typical semi-aquatic species, Damasonium alisma, to investigate the impact of ploughing at population level. We used two complementary techniques to study seed banks: hand sorting and seedling emergence. We found that species richness of seeds, seed abundance and germination ability were strongly affected by ploughing at community level. Concerning D. alisma, most of the seeds (56%) were stored in the two deepest soil layers among the four considered in ploughed pools. Moreover, the germination rate was higher for buried seeds (84%) than for seeds collected at the surface (33.6%). These patterns were almost inverted in unploughed pools. Our results agree with the temporal storage effect generally suggested to describe the seed bank property of plant communities. But in addition, we showed that ploughing induces a spatial storage effect in accumulating species and individuals in the seed banks that favourably influence community dynamics. We conclude that, in contrast to what is usually thought, ploughing disturbance can be of benefit for such ephemeral wetland vegetation.