Effect of sheep grazing on seed circulation on the Loess Plateau

In grazing ecosystems, mature seeds fall directly to the soil to form the soil seed bank (SSB), or are ingested by grazing livestock to become part of the dung seed bank (DSB; i.e., seed circulation). Both the SSB and DSB form the basis for the natural regeneration of vegetation. However, little is known about the relationships between the SSB, DSB, and aboveground vegetation (AGV) community under different stocking rates (SRs). This study investigated the relationships between the SSB, seeds in Tan sheep (Ovis aries) dung, and AGV at different SRs (0, 2.7, 5.3, and 8.7 sheep ha^–1) in a semiarid region of the Loess Plateau in China. We found that Tan sheep grazing increased the species richness heterogeneity of grassland vegetation, and negatively influenced the density of AGV. Under natural conditions, 17 species from soil‐borne seeds and 10 species from Tan sheep dung germinated. There was low species similarity between the soil and DSBs and AGV. Sheep SR and the seed banks (soil and dung) were negatively correlated with AGV. Seeds are cycled from herbage to livestock to soil during cold season grazing; the seasonal nature of this seed dispersal is an adaptation to harsh, semiarid environments. Increased seed bank diversity under sheep grazing facilitates grassland regeneration on the Loess Plateau, similarly to other semiarid regions globally.     

生物土壤结皮对荒漠土壤种子库和种子萌发的影响

研究了腾格里沙漠东南缘在不同自然条件（风、温度、水分）下,人工固沙植被区（24龄、41龄、50龄）和相邻天然植被区的两种生物土壤结皮对荒漠土壤种子库和种子萌发的影响。结果表明,荒漠土壤种子库在苔藓结皮上的储量显著高于藻类结皮。随着生物土壤结皮的发育,种子萌发量在苔藓结皮上增加,在藻类结皮上减少。生物土壤结皮层的含水量对种子萌发有显著的影响（p〈0.05）,植物种子在湿润处理的生物土壤结皮上的萌发量高于干燥处理的生物土壤结皮上的种子萌发量。生物土壤结皮表层温度和亚表层温度对荒漠植物种子萌发无显著影响（p〉0.05）,但总体而言,对于苔藓结皮,植物种子在较高温度下的萌发量略高于在较低温度下的萌发量,而对于藻类结皮,植物种子在较低温度下的萌发量略高。     

Annual plants in arid and semi-arid desert regions

Annual plants are the main vegetation in arid and semi-arid desert regions. Because of their unique traits, they are the optimal experimental subjects for ecological studies. In this article, we summarize annual plants’ seed germination strategies, seedling adaptability mechanism to environments, seed dispersal, and soil seed banks. We also discuss the biotic and abiotic factors affecting the composition and dynamics of annual plant populations and communities. Because annual plants have important ecological functions in desert vegetation systems, this study on annual plants will be of great benefit to the conservation and restoration of desert ecosystems, the rational utilization of resources, and the sustainable development of desert regions. __________ Translated from Chinese Journal of Ecology, 2006, 25(7): 851–856 [译自: 生态学杂志]     

西藏种子植物分布新资料

本文报道了分布于西藏的4个中国新记录种, 即须弥四带芹(Tetrataenium wallichii)、巴洛特栎(Quercus baloot)、尼泊尔姜味草(Clinopodium nepalense)和喜马拉雅耳稃草(Garnotia emodi); 以及24个西藏新记录种, 即翼叶棱子芹(Pleurospermum decurrens)、线叶球兰(Hoya linearis)、尼泊尔菊三七(Gynura nepalensis)、一枝黄花(Solidago decurrens)、拟游藤卫矛(Euonymus vaganoides)、云南木鳖(Momordica subangulata subsp. renigera)、马㼎儿(Zehneria japonica)、攀援胡颓子(Elaeagnus sarmentosa)、四棱猪屎豆(Crotalaria tetragona)、大叶千斤拔(Flemingia macrophylla)、毛喉鞘蕊花(Coleus forskohlii)、独龙木姜子(Litsea taronensis)、长序大苞兰(Bulbophyllum purpureofuscum)、球花石豆兰(B. repens)、黄兰(Cephalantheropsis obcordata)、双角厚唇兰(Dendrobium forrestii)、密花兰(Diglyphosa latifolia)、云南盆距兰(Gastrochilus yunnanensis)、扁茎羊耳蒜(Liparis assamica)、耳唇兰(Otochilus porrectus)、疏花无叶莲(Petrosavia sakuraii)、长序羊角藤(Gynochthodes lacunosa)、黑蒴(Alectra avensis)和赤杨叶(Alniphyllum fortunei), 其中无叶莲科为西藏新记录科, 一枝黄花属(Solidago)、马㼎儿属(Zehneria)、千斤拔属(Flemingia)、鞘蕊花属(Coleus)、密花兰属(Diglyphosa)、无叶莲属(Petrosavia)、羊角藤属(Gynochthodes)、黑蒴属(Alectra)和赤杨叶属(Alniphyllum)等9个属为西藏新记录属。凭证标本均存放于中国科学院昆明植物研究所标本馆(KUN)。     

Effect of the filling season on aquatic plants in Mediterranean temporary ponds

Aims Pond environmental conditions may differ among years with regards to the season in which ponds begin to fill. We experimentally evaluated how seedling emergence, plant growth and phenology differed among years in which filling occurred in winter, autumn or spring.Methods We collected sediments from a natural temporary pond and located them in aquariums. They were placed in a climatic chamber that simulated annual variation in field environmental temperatures and light conditions. Aquariums were assigned to one of three treatments, which differed in the date on which they were filled with water (autumn, winter and spring). We counted the number of seedlings of different species emerged and recorded data about the presence of flowers, seeds or spores every week. The experiment was finished in June, when we harvested the plants and estimated their biomass.Important findings In most species, seedling emergences were primarily related to time after filling, and thus synchronized their life cycles with the unpredictably timed wet phase of the ponds. Autumn filling resulted in the highest numbers of seeds/spores. However, winter filling promoted plant growth the most. In the spring filling treatment, more terrestrial plant seedlings emerged and fewer seeds/spores were produced. When ponds are flooded earlier, plants may produce a higher number of propagules. However, in years when inundation is delayed to spring and hydroperiods are short, seedling emergence deplete the seed bank and there is little to no seed production, while terrestrial monocots are able to colonize pond basin.     

Climate warming could shift the timing of seed germination in alpine plants

Background and Aims

Despite the considerable number of studies on the impacts of climate change on alpine plants, there have been few attempts to investigate its effect on regeneration. Recruitment from seeds is a key event in the life-history of plants, affecting their spread and evolution and seasonal changes in climate will inevitably affect recruitment success. Here, an investigation was made of how climate change will affect the timing and the level of germination in eight alpine species of the glacier foreland.

Methods

Using a novel approach which considered the altitudinal variation of temperature as a surrogate for future climate scenarios, seeds were exposed to 12 different cycles of simulated seasonal temperatures in the laboratory, derived from measurements at the soil surface at the study site.

Key Results

Under present climatic conditions, germination occurred in spring, in all but one species, after seeds had experienced autumn and winter seasons. However, autumn warming resulted in a significant increase in germination in all but two species. In contrast, seed germination was less sensitive to changes in spring and/or winter temperatures, which affected only three species.

Conclusions

Climate warming will lead to a shift from spring to autumn emergence but the extent of this change across species will be driven by seed dormancy status. Ungerminated seeds at the end of autumn will be exposed to shorter winter seasons and lower spring temperatures in a future, warmer climate, but these changes will only have a minor impact on germination. The extent to which climate change will be detrimental to regeneration from seed is less likely to be due to a significant negative effect on germination per se, but rather to seedling emergence in seasons that the species are not adapted to experience. Emergence in autumn could have major implications for species currently adapted to emerge in spring.     

植冠与土壤种子库储存种子的萌发特性及策略

为明确黄土丘陵沟壑区植物种子库如何调控种子萌发来提高个体适合度,选择研究区7种具有种子库的主要物种为研究对象,以刚成熟和室内储存种子为对照,比较植冠宿存(5个宿存期)和土壤埋藏(5a埋藏期)对植物种子萌发特性的影响,探讨植冠种子库与土壤种子库储存下的种子萌发策略。结果表明:7种植物种子经过不同种子库储存后萌发特性表现出明显的种间差异,黄刺玫(Rosa xanthina)和水栒子(Cotoneaster multiflorus)种子萌发力表现为植冠宿存不变型、土壤储存增强型,土壤储存明显提高水栒子种子萌发速率;达乌里胡枝子(Lespedeza davurica)和狼牙刺(Sophora davidii)种子萌发力表现为植冠宿存增强型、土壤储存减弱型,种子萌发历时表现为植冠宿存延长型,土壤种子库储存还可加快达乌里胡枝子萌发速率、缩短萌发历时;茭蒿(Artemisia giralaii)和铁杆蒿(Artemisia gmelinii),种子萌发率随植冠宿存时间先升高后降低,随土壤储存时间先降低后升高,土壤储存可推迟其萌发,铁杆蒿种子萌发速率在植冠与土壤储存后均加快;紫丁香(Syringa oblata)种子萌发率随植冠宿存先升高后降低,土壤储存明显加快其种子启动萌发与速率。在黄土丘陵沟壑区,植物种子经过植冠或土壤种子库储存,或增加、加快、提早萌发充分利用有利条件提高占据性,或减少、减缓、推迟萌发分摊不利条件的风险;而且该区植物植冠与土壤储存后种子萌发特性间的关系,体现各自适应环境与应对干扰的分工与协作策略,主要表现为:单一主导型和相辅相成型。     

Seed dynamics of resprouting shrubs in grassy woodlands: Seed rain,predators and seed loss constrain recruitment potential

Abstract Measuring the fate of seeds between seed production and seedling establishment is critical in understanding mechanisms of recruitment limitation of plants. We examined seed fates to better understand the recruitment dynamics of four resprouting shrubs from two families (Fabaceae and Epacridaceae) in temperate grassy woodlands. We tested whether: (i) pre‐dispersal seed predation affected seed rain; (ii) post‐dispersal seed predation limited seed bank accumulation; (iii) the size of the seed bank was related to seed size; and (iv) viable seeds accumulated in the soil after seed rain. There was a distinct difference in seed production per plant between plant families with the legumes producing significantly more seeds per individual than the epacrids. Seed viability ranged from 43% to 81% and all viable had seed or fruit coat dormancy broken by heat or scarification. Pre‐dispersal predation by Lepidopteran larvae removed a large proportion of seed from the legume seed rain but not the epacrids. Four species of ants (Notoncus ectatomoides, Pheidole sp., Rhytidoponera tasmaniensis and Iridomyrmex purpureus) were major post‐dispersal seed removers. Overall, a greater percentage of Hardenbergia (38%) and Pultenaea (59%) seeds were removed than the fleshy fruits of Lissanthe (14%) or Melichrus (0%). Seed bank sizes were small (<15 seeds m^?2) relative to the seed rain and no significant accumulation of seed in the soil was detected. Lack of accumulation was attributed to seed predation as seed decay was considered unlikely and no seed germination was observed in our study sites. Our study suggests that seed predation is a key factor contributing to seed‐limited recruitment in grassy woodland shrubs by reducing the number of seeds stored in the soil.     

Climate change and plant regeneration from seed

At the core of plant regeneration, temperature and water supply are critical drivers for seed dormancy (initiation, break) and germination. Hence, global climate change is altering these environmental cues and will preclude, delay, or enhance regeneration from seeds, as already documented in some cases. Along with compromised seedling emergence and vigour, shifts in germination phenology will influence population dynamics, and thus, species composition and diversity of communities. Altered seed maturation (including consequences for dispersal) and seed mass will have ramifications on life history traits of plants. Predicted changes in temperature and precipitation, and thus in soil moisture, will affect many components of seed persistence in soil, e.g. seed longevity, dormancy release and germination, and soil pathogen activity. More/less equitable climate will alter geographic distribution for species, but restricted migratory capacity in some will greatly limit their response. Seed traits for weedy species could evolve relatively quickly to keep pace with climate change enhancing their negative environmental and economic impact. Thus, increased research in understudied ecosystems, on key issues related to seed ecology, and on evolution of seed traits in nonweedy species is needed to more fully comprehend and plan for plant responses to global warming.     

Wheat seed ageing viewed through the cellular redox environment and changes in pH

To elucidate biochemical mechanisms leading to seed deterioration, we studied 23 wheat genotypes after exposure to seed bank storage for 6–16 years compared to controlled deterioration (CD) at 45?°C and 14 (CD14) and 18% (CD18) moisture content (MC) for up to 32 days. Under two seed bank storage conditions, seed viability was maintained in cold storage (CS) at 0?°C and 9% seed MC, but significantly decreased in ambient storage (AS) at 20?°C and 9% MC. Under AS and CS, organic free radicals, most likely semiquinones, accumulated, detected by electron paramagnetic resonance, while the antioxidant glutathione (GSH) was partly lost and partly converted to glutathione disulphide (GSSG), detected by HPLC. Under AS the glutathione half-cell reduction potential (E_GSSG/2GSH) shifted towards more oxidising conditions, from ?186 to ?141?mV. In seeds exposed to CD14 or CD18, no accumulation of organic free radicals was observed, GSH and seed viability declined within 32 and 7 days, respectively, GSSG hardly changed (CD14) or decreased (CD18) and E_GSSG/2GSH shifted to ?116?mV. The pH of extracts prepared from seeds subjected to CS, AS and CD14 decreased with viability, and remained high under CD18. Across all treatments, E_GSSG/2GSH correlated significantly with seed viability (r?=?0.8, p<.001). Data are discussed with a view that the cytoplasm is in a glassy state in CS and AS, but during the CD treatments, underwent transition to a liquid state. We suggest that enzymes can be active during CD but not under the seed bank conditions tested. However, upon CD, enzyme-based repair processes were apparently outweighed by deteriorative reactions. We conclude that seed ageing by CD and under seed bank conditions are accompanied by different biochemical reactions.     

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.     

Seed banks and seed population dynamics of halophytes

In this review I will describe the importance of seed banks and thepopulation dynamics of seeds on the distribution of species in salinehabitats. The main questions being examined in this review include: 1.Does the seed bank represent the flora of the entire salinity gradient or isit restricted to the species in each zonal community? 2. Is the size andspecies composition of the persistent seed bank regulated by the degree ofsalt stress in habitats along an environmental gradient? 3. Does thepopulation dynamics of seeds influence the temporal and spatial distributionof plant species in saline habitats? Seed banks may be transient orpersistent depending upon the physiological responses of species and thesoil environment in which the seeds are found. The formation of zonalcommunities in salt marsh environments is affected by changes in soilsalinity and flooding along an elevational gradient. Population dynamics ofseeds have been found to determine the spatial and temporal distributionof species along salinity gradients. The flora and relative density of speciesof zonal communities are significantly dependent upon the stress toleranceof species at different stages of development and the presence of transientor persistent seed banks. The occurrence of a seed bank is related to thesalinity tolerance of species at the germination stage of development, aseeds ability to tolerate hypersaline conditions and flooding, and whetheror not species are able to maintain a persistent seed bank until hypersalineconditions are alleviated.

     

持久土壤种子库研究综述

土壤种子库是指存在于土壤上层凋落物和土壤中全部存活种子,简单地可分为短暂土壤种子库和持久土壤种子库。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,休眠的种子组成了持久土壤种子库。持久土壤种子库具有在承受了空间或时间上不可预测的干扰的植被中发挥繁殖能力的潜势,因此,其在植被承受干扰后的恢复、管理和重建中常常起关键作用。研究持久土壤种子库能丰富生物多样性的内容,同时,可以为深入了解植被更新提供更多的信息。本文从持久土壤种子库的研究方法、分类方法、指示因子、生态意义,以及持久土壤种子库研究中存在的问题和今后的工作进行综述,试图为将来的工作奠定基础。     

28种禾本科植物种子形态学特征及其萌发对绵羊瘤胃消化的反应

采用瘘管羊瘤胃瘘管尼龙袋法,对北疆地区常见的28种禾本科植物种子进行不同时间段的瘤胃消化处理,对处理前后种子的长、宽、厚、形状指数、百粒重和萌发率进行了测量,研究种子对绵羊瘤胃消化的反应,以期丰富北疆地区植物种子消化道传播的内容.结果表明: 除臭草、剪股颖、鳞茎早熟禾、猫尾草和小麦以外,其余23种植物的种子均为椭圆或扁平状种子;小麦和燕麦种子百粒重分别为3.52和1.69 g,其余种子的百粒重均为0.01～1 g,属中等或偏小类型.种子经瘤胃消化后,颜色变深,种子结构被破坏,种子的芒、稃和颖等附属结构的长度随消化时间的延长逐渐减小;种子长、宽、厚、百粒重随消化时间的延长呈逐渐减小趋势,但变化不显著;种子经绵羊瘤胃消化后,萌发率显著降低,经瘤胃消化6 h后,除鹅观草和燕麦种子萌发率降为0外,其余26种植物仍有部分种子保持活力.     

Composition,size and dynamics of the seed bank in a mediterranean shrubland of Chile

Abstract Analysis was performed of the richness and abundance of woody species, forbs, and annual grasses in the easily germinating soil seed bank (henceforth seed bank) in a mediterranean shrubland of central Chile. The effects of successional development after fire and by microsite type (underneath or outside shrubs) on the density of seeds in the soil, and the relationship of species abundance in the seed bank with its abundance in the above‐ground vegetation was examined. A total of 64 plant species were recorded in the seed bank, of which 44 were annual or biannual. Eight species were woody and another eight were perennial herbs. Four could not be identified to species level. The highest richness of established herbaceous species was recorded in late spring, with 31 species. The regeneration of the herbaceous vegetation was driven by the annual production of seeds and by a reserve of short‐lived propagules in the soil. Density of all germinating seeds was significantly higher during late spring and late summer. Density of grass seeds was greater during late spring, while that of all other species was greater during late summer. Annual grass seeds accumulated in higher proportion at exposed microsites rather than under woody canopy, and in young (< 5 years old) and intermediate‐age patches (10–20 years old) rather than in mature vegetation (30–50 years old). The abundance of established woody and herb species was uncorrelated with that of the seed bank.     

Types of pollination and seed dispersal in Mediterranean plants

Abstract

Selected examples of pollen and seed dispersal in Mediterranean plants are described. The aspects of pollination considered are: comparison between cleistogamous and chasmogamous forms in the same species; differences in attractants and rewards; duration of pollen viability according to pollination syndrome. The aspects of seed dispersal considered are: presence or absence of specialized structures for dispersal; examples of active, passive and induced dispersal; animals involved in seed dispersal and their reward; type and functions of elaiosomes.     

冷蒿草原土壤可萌发种子库特征及其对放牧的响应

（１）采用萌发试验法对内蒙古冷蒿（Ａｒｔｅｍｉｓｉａ ｆｒｉｇｉｄａ）草原土壤种子特征及其在不同放牧压力下的变化进行了研究。（２）冷蒿草原可萌发种子库由４种多年生禾草,１１种种多年生杂草及３种１年生植物所组成。（３）每样中的可萌发种子是变化于４５到３０５之间,平均１０２／样。多年生禾草、多年生杂类草及１年生植物的土壤中种子量分别占总可萌发种子库的４６．５７％、５１．９６％和１．５７％。多年和禾 草     

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.     

面积和中间膨胀效应对丽江地区种子植物物种丰富度垂直分布格局的影响

滇西北地区是我国三大特有物种分化中心之一。作者利用地方植物志资料,结合数值高程模型(DEM)数据,研究了云南丽江地区种子植物物种丰富度的垂直分布格局,并分析了面积和中间膨胀效应(mid-domaineffect)对该格局的影响。研究结果表明:随着海拔的升高,各海拔段面积呈先增加后下降的分布格局;物种丰富度、物种密度和中间膨胀效应的物种丰富度预测值在海拔梯度上均呈单峰型变化格局。面积和中间膨胀效应对丽江地区物种丰富度的垂直分布格局有着显著的影响。其中,面积起主要作用,对物种丰富度的变异解释百分率达80.2%,而中间膨胀效应的影响作用相对较小,仅占11.3%。     

Ecological and morphological seed traits of Polygala sardoa and P. sinisica: A comparative study on two endemic species of Sardinia

Polygala sardoa Chodat and P. sinisica Arrigoni (Polygalaceae) are two exclusive endemics to Sardinia and P. sinisica is affiliated under “Critically Endangered” in the IUCN Red Lists. In this work comparative studies on two populations of P. sardoa and in the only one of P. sinisica were carried out. In particular, seed output calculations and morphometric measurements on seed and elaiosome sizes were carried out. The effect of chipping, constant (15 °C) and alternating (25/10 °C) temperature regimes and light (8 h irradiance/day and dark) on germination were investigated. Seedling vigor assessments and a study on seed persistence in the soil were also carried out. P. sinisica had a higher seed output than P. sardoa and P. sinisica seeds were smaller than those of P. sardoa, with lower elaiosome area and elaiosome ratio values. Neither species had alternating temperature or light requirements for germination. P. sardoa achieved high germination percentages (> 80%) at all the tested conditions. P. sinisica had a lower maximum germination (<60%), suggesting the presence of physiological dormancy, and took more than twice as long to reach the maximum germination percentage. Seedlings of P. sardoa were larger than those of P. sinisica, and neither species formed a persistent soil seed bank. These new data may help implement effective conservation measures for these two species and, more generally, for threatened endemic species of this genus.