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。     

松嫩草地水淹干扰后的土壤种子库特征及其与植被关系

研究了松嫩平原羊草草地不同强度水淹干扰对土壤种子库种类组成、物种多样性及其与植被物种组成的相似性关系等的影响。结果表明：（1）随着水淹强度的加重或水淹持续时间的延长,相应地段的土壤种子库物种数目和种子存量都呈减小趋势;（2）土壤种子库的种类成分在干扰样带和对照样带间差异明显,而受水淹干扰的样带之间种子库的种类组成差异不大,表明洪水漂移行使了繁殖体传播和散布的功能;（3）随水淹干扰强度增加,种子库物种多样性指数减小;（4）种子库与地上植被物种组成相似性普遍较低,其原因是主要靠营养繁殖以更新种群的多年生根茎植物经常在植被中出现而不在种子库中出现;（5）种子库与地上植被物种组成相似性随水淹干扰强度增加而下降,表明了水淹干扰对种子库与地上植被物种组成相似性有一定程度的影响。     

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。     

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。     

铜尾矿废弃地与相邻生境土壤种子库特征的比较

土壤种子库是植被群落的重要组成部分,其特征决定了群落的演替方向。对铜陵杨山冲尾矿库6个植被群落及相邻两处生境的土壤种子库进行了研究。结果表明,尾矿内各植被群落种子库的种子密度间存在较大差异,变化范围为57—593粒/m2,平均种子密度为370粒/m2,尾矿坝体和周围山体种子库种子密度分别为999和121粒/m2,各样地土壤中种子均主要集中在0—5 cm范围内。尾矿种子库与坝体种子库间的相似性指数大于其与周围山体种子库的相似性指数,但尾矿内各植被群落种子库间的相似性较差,相似性指数的变化范围为0.308—0.636。可见,群落微生境对土壤种子库的种子密度和物种组成产生了较大的影响。尾矿种子库种类与地上植被的平均相似指数为0.355,低于坝体种子库种类与地上植被相似性系数。3处样地土壤种子库的物种多样性、丰富度和均匀度指数均表现为坝体>尾矿>山体。尾矿种子库在农田土壤中萌发并正常生长的幼苗为16科44属53种,而在尾矿基质中仅为9科36属45种,均以禾本科、菊科和豆科植物萌发和生长状况较好,这3科构成了尾矿地上植被的主要类型。尾矿种子库在尾矿基质中萌发成活率为62.2%—91.2%,约为坝体和山体土壤种子库在尾矿基质中萌发成活率的2倍。说明,组成尾矿种子库的种子大部分已经适应了尾矿的极端恶劣环境或者其本身就是耐性极强的植物类型。     

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.     

西双版纳热带森林土壤种子库与地上植被的关系

通过实验研究探讨了西双版纳几类热带森林的土壤种子库与地上植被的关系．结果表明,在森林演替的初期,土壤种子库与地上植被共有的种类和种子储量较多,随着林龄的增大,外来种子的比例逐渐增加,到季节雨林阶段,土壤种子库中的种子大部分为来自群落外的先锋种类．这些种子在郁闭的林冠下很难萌发,一旦森林受到干扰出现林窗或空旷地,这些潜在的种源将迅速萌发,参与植被的恢复或演替     

湿地土壤种子库与地上植被相似性关系研究评述

土壤种子库与地上植被的关系是土壤种子库研究的重要组成部分。当前,湿地生态系统面临严重威胁,研究湿地土壤种子库和地上植被关系既可以加强对土壤种子库和植物群落特征的认识,又可以为湿地保护与管理提供理论指导。检索了科学引文索引扩展版(SCIE)数据库中收录的1900—2012年间研究湿地土壤种子库与地上植被关系的文献,通过分析土壤种子库与地上植被的Srensen相似性系数,结果发现:不同湿地类型的土壤种子库和地上植被的相似性存在显著差异,河流湿地中两者的相似性最小;不同植被类型中土壤种子库与地上植被的相似性差异显著:草本群落的相似性大于乔木群落;不同气候带的湿地中两者的相似性也存在显著差异,其中亚热带地区相似性最小。总结了湿地种子库与地上植被相似性关系的时空变化特征。二者的相似性通常随着植物群落的演替而减小,在空间上也随着环境梯度而变化。分析了两者关系的影响因素,如种子传播、环境条件和繁殖策略等。对研究中存在的问题及发展方向提出建议。     

沙坡头地区生物结皮覆盖区土壤种子库组成及垂直分布特征

采用野外随机取样和室内萌发试验相结合的方法,对沙坡头人工植被区的藓类结皮、地衣结皮和裸沙覆盖区土壤种子库的组成及垂直分布特征进行了研究。结果表明:1)人工植被区土壤种子库的物种组成简单,以1年生草本为主,相较于裸沙,两种生物结皮的存在显著增加了土壤种子库的密度(P0.01),但降低了土壤种子库的物种多样性及其与地上植被的相似性;2)两种生物结皮覆盖区土壤种子库的总密度虽无显著差异,但在0—2 cm土层中,地衣结皮土壤种子库的密度显著高于藓类结皮(P0.05),而在2—5 cm和5—10 cm土层中,藓类结皮土壤种子库的密度高于地衣结皮,但差异不显著;3)不同生物结皮覆盖区土壤种子库的垂直分布特征存在差异,藓类结皮覆盖土壤中有活力的种子主要分布在0—5 cm土层中,而地衣结皮和裸沙覆盖土壤中有活力的种子主要分布在0—2 cm土层中,且随着深度的增加,土壤中有活力的种子急剧减少。该研究表明,相较于裸沙,生物结皮的存在不仅增加了土壤种子库的大小,还改变了土壤种子库的垂直分布格局。生物结皮层下仍有相当比例有活力的小种子,这些种子欠缺萌发条件,对地上植被的贡献作用较小,但它们的存在对荒漠生态系统健康及可持续发展具有重要意义。     

淡水湿地种子库的研究方法、内容与展望

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.种子库的研究是深入探讨湿地植被结构、功能与动态等方面的重要基础,同时也是对湿地生物多样性研究的一个重要补充,对于了解植被演替动态、植被更新和受损湿地植被重建与恢复具有指导意义.本文结合国内外淡水湿地种子库研究现状,对湿地种子库的形成、研究方法以及湿地种子库时空格局、种子库与地表植被的关系、水文变化对湿地种子库的影响、湿地种子库在湿地恢复中的应用等主要研究内容进行了系统的总结;同时对湿地种子库的时间动态、种子库的分类、种子库与地表植被的关系、湿地恢复重建及湿地景观营造等研究进行了展望.     

Species trait shifts in vegetation and soil seed bank during fen degradation

Fens in Central Europe are characterised by waterlogged organic substrate and low productivity. Human-induced changes due to drainage and mowing lead to changes in plant species composition from natural fen communities to fen meadows and later to over-drained, degraded meadows. Moderate drainage leads to increased vegetation productivity, and severe drainage results in frequent soil disturbances and less plant growth. In the present article, we analyse changes in plant trait combinations in the vegetation and the soil seed bank as well as changes in the seed bank types along gradient of drainage intensity. We hypothesize that an increase in productivity enhances traits related to persistence and that frequent disturbance selects for regeneration traits. We use multivariate statistics to analyse data from three disturbance levels: undisturbed fen, slightly drained fen meadow and severely drained degraded meadow. We found that the abundance of plants regenerating from seeds and accumulating persistent seed banks was increasing with degradation level, while plants reproducing vegetatively were gradually eliminated along the same trajectory. Plants with strong resprouting abilities increased during degradation. We also found that shifts in trait combinations were similar in the aboveground vegetation and in soil seed banks. We found that the density of short-term persistent seeds in the soil is highest in fen meadows and the density of long-term persistent seeds is highest in degraded meadows. The increase in abundance of species with strong regeneration traits at the cost of species with persistence-related traits has negative consequences for the restoration prospects of severely degraded sites.     

Regenerative role of seed banks following an intense soil disturbance

Our main aim was to determine the contribution of the seed bank to vegetation regeneration following a disturbance consisting in a deep ploughing and a thorough homogenisation of a perennial grassland. In the seed bank prior to disturbance, seed distribution through the vertical soil profile was evaluated to determine the initial seed species structure. Then, several characteristics of the shallow seed bank and the extant vegetation were evaluated prior and following field disturbance: seed species composition and abundance, and species composition of the aboveground vegetation. The contribution of seed rain versus seed bank was evaluated by means of the comparison of the vegetation developed in plots filled with sterilised soil (seed bank removal) and the vegetation developed in non-sterilised plots in the field. The distribution of seeds through the profile indicated a sharp decline in abundance with depth, and it was probably linked to propagule morphology, with small and rounded seeds proner to being buried deeper than larger seeds. In the grassland prior to disturbance, the aboveground vegetation and seed bank species composition showed very low similarity index, most likely because during the 5 years following field abandonment, sheep pressure had caused a faster change in aboveground vegetation species composition than in seed bank species composition. Ploughing and homogenisation of the grassland led to low seed abundance in the shallow soil layer caused by dilution of the seed bank. Regardless of impoverishment in seed abundance and species richness, comparison between sterilised and non-sterilised plots showed that the seed bank acted as an effective source of colonising species and determined the aboveground species composition. To summarise, this study outlines the importance of considering several characteristics of the seed bank, such as species composition and seed abundance, in the understanding of the function of seed bank and dynamics of the vegetation following a deep ploughing and homogenisation treatment.     

The relationship between soil seed bank,above‐ground vegetation and disturbance intensity on old‐field successional permanent plots

Questions: How does disturbance and successional age influence richness, size and composition of the soil seed bank? What is the potential contribution of the soil seed bank to the plant community composition on sites differing in their successional age or disturbance intensity? Location: Experimental Botanical Garden of Göttingen University, central Germany. Methods: Above‐ground vegetation and soil seed bank were studied on formerly arable fields in a 36‐year‐old permanent plot study with five disturbance intensities, ranging from yearly ploughing via mowing to long‐term uninterrupted succession. We compared species compositions, seed densities and functional features of the seed bank and above‐ground vegetation by using several methods in parallel. Results: The seed bank was mainly composed of early successional species typical of strongly disturbed habitats. The difference between seed bank composition and above‐ground vegetation decreased with increasing disturbance intensity. The species of greatest quantitative importance in the seed bank was the non‐native forb Solidago canadensis. Conclusions: The ability of a plant community to regenerate from the soil seed bank dramatically decreases with increasing time since abandonment (successional age) and with decreasing disturbance intensity. The present study underlines that plant species typical of grasslands and woodlands are limited by dispersal capacity, owing to low capacity for accumulation of seeds in the soil and the fact that most species do not build up persistent seed banks. Rare and target species were almost absent from the seed bank and will, after local elimination, depend on reintroduction for continuation of their presence.     

Soil seed bank characteristics in Cameroonian rainforests and implications for post-logging forest recovery

The soil seed bank is considered as an important component for resilience of climacic vegetation. Whereas several related studies have been conducted in Asian, American and some African tropical forests, no investigation has ever been conducted in Central African rainforests, especially in logged forests where the soil seed bank could contribute to regeneration of timber of trees species. We studied the soil seed bank characteristics in relation to the standing vegetation in three Cameroonian forest zones with different disturbance regimes. There was no significant difference between sites in terms of density of the seed bank; the average mean density was 87.6 seeds m⁻². But dissimilarities of the floristic compositions between sites were quite high. Overall, seeds came from 43 species including three commercial tree species. Whereas the seedlings emerging from soil samples mostly came from weedy and short-lived pioneer species, climax species predominated in the extant vegetation, leading to a very weak similarity between soil seed flora and the surrounding vegetation: Sorensen's index ranged from 3.5 to 7.6%. Canopy openness could significantly affect the species richness of soil seed stocks but not the seed density. These results show that the soil seed bank contribution to the resilience of mature tropical forests is low. In particular, very few timber tree species could benefit from soil seed stocks for their regeneration. Therefore, the development of enrichment techniques including use of the soil seed bank as a source of tree regeneration in such a context would be irrelevant.     

The role of soil seed banks in the restoration of dry acidic dune grassland after burning of Ulex europaeus scrub

Question: Can the seed bank play a significant role in the restoration of plant communities of dry acidic dune grassland where fire has destroyed Ulex europaeus scrub? Location: Northern French Atlantic coast. Methods: One year after the fire, the seed bank and vegetation were sampled in 1 m × 1 m plots along three transects from the oldest scrub vegetation towards the grassland. Differences in species richness, seed density and contribution of ecological groups in the seed bank and vegetation along the transects were analysed. Results: Seed density and species richness in the seed bank decreased significantly from the grassland towards the centre of the scrub vegetation; 50% of the seed bank consisted of core species of the target plant community, such as Carex arenaria, Aira praecox, Rumex acetosella and Agrostis capillaris. Seeds of these species were also found in the deeper soil layers beneath the oldest scrub vegetation, indicating that they can be considered to be long‐term persistent. Beneath the youngest scrub vegetation, seeds of rare satellite target species also occurred. However, no target species were established on the burned site after one year, resulting in a large discrepancy between seed bank and vegetation. Conclusions: Although the seeds present in the soil indicate that restoration of the acidic grassland based on the seed bank is possible, additional management actions such as mowing and soil disturbance may be necessary to restrict resprouting of Ulex and to stimulate the germination of seeds of target species in the deeper soil layers.     

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.     

The dynamics of three shrub species in a fire-prone temperate savanna: the interplay between the seed bank, seed rain and fire regime

A model was developed to assess how the seed rain and fire regime affect seed bank dynamics and seedling establishment of three native shrub species (Acanthostyles buniifolius, Baccharis pingraea and Baccharis dracunculifolia) with different regeneration strategies, in temperate South American savanna. Seed bank and seed rain were quantified for each species under different fire regimes, and their relative roles in regeneration were evaluated. All species had short-term persistent seed banks and high annual variability in seed production. A high proportion of seeds deposited in the seed rain produced seedlings after fire; few entered the soil seed bank. Fire killed a high proportion of the seeds in the soil seed bank. Seedlings derived from the seed rain had a higher probability of surviving for 2 years than seedlings emerging from the soil seed bank. In the absence of fire, establishment depended on germination both from the seed rain and the soil seed bank, whereas with annual fire, establishment was primarily dependent on germination of seeds arriving in the annual seed rain, regardless of species’ regeneration strategies. These results help to explain changes in the vegetation of South American temperate savannas as a result of changes in fire regime and grazing management during the last 50 years. By revealing the crucial roles of the soil seed bank and seed rain in regeneration, this study provides vital information for the development of appropriate management practices to control populations of shrub species with different regeneration strategies in South American temperate savannas.     

Effects of disturbance intensity on seasonal dynamics of alpine meadow soil seed banks on the Tibetan Plateau

Background and Aims

Information on soil seed bank processes is crucial for understanding vegetation dynamics. Despite the documented importance of soil seed banks in many ecosystems, their role is not fully understood in some sensitive habitats, such as the alpine meadows of the Tibetan Plateau.

Methods

We studied the seasonal dynamics of the germinable soil seed bank under four disturbance intensities in an alpine meadow on the Tibetan Plateau as well as seed size distribution relative to disturbance intensity. Composition of the seed bank was compared with that of the standing vegetation.

Results

Density of buried seeds increased with disturbance intensity, but species richness and species diversity decreased. Seed density and species richness of the seed bank varied seasonally in all layers (0–2, 2–7, 7–12 cm) and the whole (0–12 cm). The species composition of seed bank was not significantly influenced by season. There was no trend in seed size distribution as disturbance increased. Seasonal seed bank turnover rates increased with increase in disturbance. The result of the NMDS showed that species composition of seed bank and vegetation exhibited a fairly uniform pattern in each season.

Conclusions

Although as a whole the species composition of the vegetation and seed bank showed a relatively low degree of similarity in each season, similarity was highest in the most disturbed habitat. There was no alteration in species composition of seed bank regardless of disturbance intensity, but seed density decreased as disturbance increased. Disturbances in alpine plant communities might increase persistence of regeneration niches. Regeneration from the seed bank together with vegetative reproduction contributed to aboveground vegetation in highly disturbed habitats. Clonal species played an important role in regeneration of vegetation in slightly disturbed areas, where there was little contribution of ruderals from soil seed banks.     

Experimental demography of the rare Gentianella germanica: seed bank formation and microsite effects on seedling establishment

The persistence of populations of short-lived species requires regular reproduction and seedling establishment. A persistent seed bank can buffer populations against extinction in unfavourable years. We experimentally investigated seed fate in Gentianella germanica, an endangered biennial species characteristic for species-rich nutrient-poor calcareous grasslands in central Europe. We studied the effect of experimental gaps on seedling establishment from sown seeds and the fate of seeds buried in bags over two years. In December 1993 experiments were established at seven calcareous grassland sites in the Swiss Jura mountains. In spring 1994 seedlings emerged in all plots where seeds had been sown, including previously unoccupied patches. This suggests that limited dispersal within sites contributes to small population sizes. Significantly more seedlings emerged at sites with current populations of G. germanica than at unoccupied sites (5.95% vs 3.40%). Because this difference was not explained by germinations from the natural seed bank it indicates differences in habitat quality. Clipping of the vegetation and disturbance of the soil reduced vegetation cover in the following spring and enhanced seedling emergence. In undisturbed plots 4.5% of seeds sown produced a seedling in spring 1994, whereas in plots with clipped vegetation 9.9% and in disturbed plots 12.7% produced seedlings (p>0.01). This suggests that management measures which create gaps in the vegetation (e.g. grazing) could positively influence population size and persistence of G. geymanica. On average, we recovered 7.55% viable seeds after one year of burial in bags, and 4.05% after two years, indicating that G. geymanica has a persistent seed bank. The demographic data indicate that the number of viable seeds in the seed bank exceeds the number of established plants in a population at least by a factor of 20. Restoration of extinct populations of the species from the seed bank may thus be possible if appropriate management measures are taken within a few years.