共查询到20条相似文献，搜索用时 31 毫秒
1.
Morphological and functional characteristics of flowers may have major effects on their reproductive success. Here, we report a study on the characteristics of flowers of Petrocoptis viscosa, a herb species endemic to the northwest Iberian Peninsula, restricted to crevices in limestone outcrops, and currently occurring in only three populations within an area of less than 30 km2. We also investigated the effects of pollen source on indicators of reproductive success. The results show that Petrocoptis viscosa flowers are well adapted to autogamy. Inbreeding depression (as determined by comparison of results obtained after selfing and outcrossing) was negligible for fruit production (δ=−0.05) and mean seed number (δ=−0.11), low for seed germination percentage (δ=0.08), but relatively high for mean seed weight (δ=0.23). The spatial structure and small size of population of Petrocoptis viscosa may mean that inbreeding is frequent in natural habitats. Adaptation of plants to autogamy may therefore be energetically beneficial (i.e. less wasted expenditure on rewards and flowers). 相似文献
2.
Many ecological studies have pointed out maternal effects in plants and shown that plant maternal environment influences germination of their seed and subsequent seedling growth. However, few have tested for maternal effects induced by soil macroorganisms. We tested whether two earthworm species (Aporrectodea caliginosa and Lumbricus terrestris) trigger such maternal effects on seed germination and seedling growth of three plant species (Veronica persica, Poa annua and Cerastium glomeratum). Our results show that, through maternal effects, A. caliginosa enhanced seed germination (V. persica and P. annua) and seedling growth (C. glomeratum and P. annua) while L. terrestris reduced seed germination only in V. persica. In some cases, the increase in germination rates of seeds produced in the presence of earthworms was associated with a reduction of nitrogen content in seeds. These results show that earthworms induce maternal effects in plants and that the size and direction of these effects depend on the combination of plant and earthworm species. 相似文献
3.
Tropical forest fragmentation affects animal and plant populations in different ways. For plants, early stages (seed to seedling) are more sensitive to habitat alteration than adults, and can shape their future spatial patterns. Therefore, studying how seed germination and seedling growth and survival vary at different spatiotemporal scales enhances our understanding about plant recruitment in fragmented ecosystems. In this study we examine if, and to what extent, recruitment at early life-stages of Xymalos monospora (Monomiaceae), a bird-dispersed Afrotropical tree, differs between and within forest fragments that vary in size, surrounding matrix and microhabitats. Three years of field experiments (2004-2006) in south-east Kenya, revealed that patterns of seed germination and seedling survival and growth were largely inconsistent, both in space and time. Recruitment was not consistently higher in larger or less disturbed fragments. At smaller spatial scales within forest fragments, recruitment was subject to high between-year variation too, with decreased germination in gaps only in the dry year of 2004. However, performance of seeds and seedlings was consistently better away from than under conspecific fruiting trees. Our results imply that fragmented tree populations of X. monospora may become age-structured, or ultimately go extinct, if recruitment fails in subsequent years. This may especially affect populations in small, disturbed forest fragments, where seed dispersal and buffering against stochastic processes are generally reduced. Exotic plantations bordering indigenous forest fragments may provide suitable conditions for native tree recruitment; hence, forest expansion through enrichment planting should be considered in future conservation plans. 相似文献
4.
Recent studies have shown that the introduction of non-native earthworms in previously earthworm-free soils may have negative impacts on the recruitment of certain understory plant species in northern temperate forests. There is a need, therefore, to understand the mechanisms that may underlie this phenomenon. A microcosm study was conducted to test the effects of the anecic earthworm, Lumbricus terrestris L., on the number of days for germination, % seed germination, seedling survival and seedling biomass of 14 tree species native to southern Quebec (Canada). Seeds of these species were germinated and grown in the presence or absence of L. terrestris. The presence of earthworms significantly reduced % seed germination of seven tree species, as well as seedling survival of three tree species. The germination date of three tree species was significantly affected, either positively or negatively, by the presence of earthworms. Earthworms had no effect on seedling biomass. Results suggest that the introduction of L. terrestris into forested ecosystems of southern Québec may potentially alter overstory composition through several mechanisms that differentially affect the recruitment of various tree species in the understory. 相似文献
5.
以采集于河西走廊中部荒漠边缘的苦豆子(Sophora alopecuroides L.)和披针叶黄华(Thermopsis lanceolate L.)种子为试验材料, 以不同渗透势PEG-6000 溶液模拟干旱条件, 研究了2 种植物种子萌发和幼苗生长对干旱胁迫的响应特征。研究结果显示, 随着干旱胁迫程度的加剧, 2 种植物种子吸胀速率、萌发率、萌发指数、活力指数、苗高、根长和组织饱和含水量等指标均表现出明显降低趋势, 而幼苗干重、根干重和根冠比均呈先升后降趋势。2 种植物种子萌发对干旱胁迫均较为敏感, 苦豆子和披针叶黄华种子能够萌发的最低渗透势阈值分别为-0.65 MPa 和-0.42 MPa。2 种植物因干旱胁迫未能萌发的种子复水后萌发率均较高。分析认为, 2 种植物种子萌发和幼苗生长对干旱胁迫的响应特征对幼苗的成功定植和种群的自然更新具有重要生态学意义, 但在人工栽培时保证土壤墒情应是保障建植成功的关键措施。 相似文献
6.
Terrestrial orchids typically produce numerous small seeds that contain very small nutrient reserves. The seeds are structurally adapted for wind dispersal but little is known about their fate after dispersal. Some studies of seed viability in situ indicate survival for up to two years in temperate orchid species. Seeds stored in the laboratory may last much longer. We investigated seed viability of seven North American orchid species with seed packets buried in a range of soil and wood substrates within their natural habitats. In Goodyera pubescens most seeds germinated within one year. Four other species continued to germinate sparsely during the observation period, but after almost seven years many seeds were still viable. In one species, Liparis liliifolia, seeds that had been in situ for four years had germination rates as high as 68% when sown in vitro with a compatible fungus. The remaining two species did not germinate during the observation period but the seeds were judged to be intact and tested positively for viability after four years in the ground. These observations are interpreted as different species-specific strategies for in situ germination and their seed bank potential is discussed. 相似文献
7.
Flowering phenology, soil seedbank and the impact of fire, weeds and grazing were investigated in two rare Acacia taxa restricted to the agricultural district north of Perth Western Australia. Acacia aprica is known from six extant populations and one extinct population. Five of the extant populations are restricted to linear road reserves with the sixth population located in a small native vegetation remnant. Acacia cochlocarpa ssp. cochlocarpa is known from a single population also situated on a road verge. Size class structure, levels of canopy death and an absence of juveniles indicated that all populations are in decline. Flowering intensity and success varied between populations and years in A. aprica and between years in A. cochlocarpa ssp. cochlocarpa. Seed bank analysis indicated that seeds were patchily distributed while experimental fires demonstrated that such events could break seed dormancy and promote germination. Both taxa have similar germination physiologies and showed increased germination after seeds were exposed to heat. Following emergence, however, competition with annual weeds had a negative impact on seedling growth and survival in both taxa. While vertebrate grazing had some influence, weeds were the major inhibitory influence on recruitment. Reduced fire frequencies since fragmentation may be responsible for population decline in both taxa but other site specific factors such as weeds and grazing may affect the establishment of seedlings following fire. 相似文献
8.
Susana Guill��n Teresa Terrazas Erick De la Barrera Alejandro Casas 《Genetic Resources and Crop Evolution》2011,58(3):409-423
Germination of wild and managed populations of columnar cacti was compared to analyze differences associated to management intensity. The species studied: Polaskia chende, Escontria chiotilla, Myrtillocactus schenckii, Polaskia chichipe, and Stenocereus pruinosus are in a gradient from lower to higher management intensity, respectively. Within each species wild, silvicultural, and cultivated populations also represent a gradient from lower to higher management intensity. We hypothesized that seeds of plants under higher management intensity would require more water to germinate than others since managed environments are relatively wetter than unmanaged environments. Such pattern could be visualized within and among species according to management intensity. We tested germination of seeds from different populations of the different species to the water potentials: 0.0, ?0.2, ?0.4, ?0.6, ?0.8, and ?1.0 MPa. In all species studied seeds of managed populations had significantly more mass than seeds from wild populations. Each species had different susceptibility to water availability decrease, which could be related to particular adaptations to drought resistance. Stenocereus pruinosus and Polaskia chende were the most and least susceptible species, respectively. In control treatments of all species, seeds of managed populations had higher germination rate than seeds from wild populations, but when water availability decreased the pattern was the contrary. Our results suggest that artificial selection for larger fruits and heavier seeds in plants established in wetter environments have affected germination patterns. Although species have particular critical points of water availability for germination, differences in germination patterns are more pronounced according to management and artificial selection intensity. 相似文献
9.
Calcareous grasslands are among the most diverse habitats, supporting species-rich vegetation. Propagule limitation and availability of microsites for germination represent major constraints to the successful restoration of these grasslands. To date, little information is available on the effectiveness of seed addition and soil disturbance on the restoration success of encroached semi-natural calcareous grasslands. Here, we conducted a 1 year before – 9 year after control-impact (BACI) study aimed at testing the effect of the addition of seeds of native species and livestock grazing on calcareous grasslands. Each restoration measure and their combination differed in their impact on these communities and varied over time. Grazing had a significant, beneficial, impact on these communities, although the impact was species-specific. On average, grazed plots were characterized by a higher number of species and a lower vegetation cover. Nine years after treatment application, grazed site were dominated by Trifolium incarnatum subsp. molinerii, Xeranthemum cylindraceum, Orlaya grandiflora, Teucrium chamaedrys and Bromus erectus while ungrazed sites were dominated by B. erectus, X. cylindraceum, O. grandiflora and Prunus spinosa. Only 8 out of 34 species responded significantly to disturbance or/and disturbance and seed addition while 22 species were significantly affected by the sampling year and 18 by a blocking factor. The low recruitment from added seeds and the fact that seed addition is a time-and labor-consuming activity suggests that an adequate level of disturbance and natural regeneration represent the most cost-effective approach to the restoration of these calcareous grasslands. 相似文献
10.
A semi-annual eelgrass (Zostera marina L.) population became extinct in 2004. It had flourished for many decades at Terschelling in the western Wadden Sea, one of the most eutrophied locations where seagrass growth has been recorded. Semi-annual populations survive the winter season by seed (annual), and by incidental plant survival (semi-annual). We compared seed bank dynamics and fate of plants between this impacted site and a reference site in the winter of 1990-1991. Seed bank density at Terschelling was extremely low (5-35 seeds m−2) in comparison to the reference site (>60 seeds m−2) and also in comparison to seed bank densities of (semi-)annual eelgrass populations in other parts of the world. Plant survival during winter was nil. Nevertheless, the population more than doubled its area in 1991, implying maximum germination and seedling survival rates. However, from 1992 onwards the decline set in and continued - while the nutrient levels decreased. To establish the cause of the low seed bank density, we conducted a transplantation experiment in 2004 to study the relationship between seed production and macro-algal cover. The transplantation experiment showed a negative relationship between the survival of seed producing shoots and suffocation by macro-algae, which is associated with light limitation and unfavourable biogeochemical conditions. The plants died before they had started to produce seeds. Thus, it is likely that macro-algal cover was responsible for the low seed bank density found in Terschelling in 1990-1991. Both the recorded low seed bank density and absence of incidental plant survival during winter were related to eutrophication. These parameters must have been a severe bottleneck in the life history of the extinct population at the impacted site, particularly as Z. marina seed banks are transient. Therefore we deduce that this population had survived at the edge of collapse, and became extinct after a small, haphazard environmental change. We argue that its resilience during these years must have been due to (i) maximum germination and seedling survival rates and (ii) spatial spreading of risks: parts of the population may have survived at locally macro-algae-free spots from where the area could be recolonised. As a consequence, the timing of the collapse was unpredictable and did not synchronise with the eutrophication process. The lesson learnt for conservation is to recognise that eutrophication may be a cause for seagrass population collapse and its eventual extinction, even years after nutrient levels stabilised, or even decreased. 相似文献
11.
Earthworms were shown to significantly affect seeds and seedlings survival via their ingestion and digestion for nutritive purposes. Such selective feeding of earthworms on plant seeds is likely to favour certain plant species and to affect seed bank composition, plant recruitment and plant community structure. Relationships between earthworms and seeds, particularly seed traits that determine attractiveness of seeds for earthworms, are yet to be determined. In this study, the influence of six seed traits was tested on the ingestion, digestion and germination of seeds by two earthworm species (Lumbricus terrestris, anecic and Satchellius mammalis, epigeic). The seed traits tested were their length, width, weight, shape, oil content and the presence of trichomes on their surface. Each earthworm species was introduced into a microcosm with eleven seed species from a chalk grassland that represented those different traits. Ingested, digested and germinated seeds were counted after voiding the guts of the earthworms. Univariate and multivariate analyses showed that seed length, width, weight and seed oil content could significantly affect the ingestion of seeds for both earthworm species. Seed width and seed oil content were the two traits that influenced the digestion of seeds the most, but only for L. terrestris. We also found that seed ingestion was earthworm species-specific but we found no correlation between earthworm traits and number of ingested or digested seeds. Few seeds germinated from L. terrestris casts and no seeds germinated from S. mammalis casts. Implications in terms of plant evolution strategies are further discussed. 相似文献
12.
Colin J. Yates Carole Elliott Margaret Byrne David J. Coates Richard Fairman 《Biological conservation》2007,136(2):306-314
In this study we investigate the effect of population size on the proportion of flowers that produce a fruit (fruit set), the number of seeds per fruit (seed set), seed germinability, seedling mortality and growth in a range of population fragments for the bird-pollinated mixed mating system shrub Calothamnus quadrifidus R. Br. (Myrtaceae). We found no significant linear relationship (p < 0.05) between population fragment size and fruit set in any of the three years reproduction was studied. In contrast, we found a very strong positive correlation between the number of seeds produced per fruit and increasing population fragment size for each of the three years. We found no significant linear relationships between population fragment size and seed germination, or seedling growth and mortality. The most plausible explanation for the decline in seed set is increased inbreeding in smaller populations. Although a previous mating system analysis with allozymes did not reflect the above, we present evidence from other lines of inquiry to indicate that inbreeding does increase in smaller populations, but is masked by post-zygotic lethal systems that eliminate genetically incompetent homozygous embryos. We found no evidence that highly mobile pollinators transporting pollen among fragments rescue small fragments from inbreeding. We discuss the implications of our findings for the conservation of plant diversity in fragments of species rich Mediterranean climate shrublands. 相似文献
13.
干旱胁迫对窄叶鲜卑花种子萌发及幼苗生长的影响 总被引：1，自引：1，他引：0
[目的]研究干旱胁迫对窄叶鲜卑花种子萌发及幼苗生长的影响,为野生种驯化和种群恢复提供参考。[方法]以窄叶鲜卑花种子为实验材料,采用不同浓度聚乙二醇(PEG-6000)模拟干旱胁迫环境,研究干旱协迫强度对窄叶鲜卑花种子的吸胀速率、发芽率、发芽势、发芽指数、活力指数和种子抗旱萌发指数及幼苗生长情况的影响。[结果]随着干旱胁迫程度的加剧,窄叶鲜卑花种子的吸水过程表现出急速吸水期、缓慢上升期和吸水平稳期3个阶段;其发芽率、发芽势、发芽指数、活力指数和种子抗旱萌发指数及苗高、根长,苗重与胁迫强度均呈负相关;当PEG浓度达30%时,种子萌发完全被抑制。另一方面,种子群体萌动、萌发和出苗达50%所需时间随胁迫强度的增加而越发延迟,且各阶段对环境临界水势要求不同,出苗阶段最为严格,表明种子出苗过程对环境水分胁迫较为敏感,耐旱能力较弱。[结论]干旱胁迫显著抑制了窄叶鲜卑花种子的萌发和幼苗生长,也说明水分是窄叶鲜卑花种子萌发和幼苗形成的主导因素之一,在较干旱地区种植需要考虑水分的供给。 相似文献
14.
《Biological conservation》2002,103(2):151-161
In this paper we assess the conservation status of five of the most threatened species in the Pyrenean range (listed in the European Habitats Directive), and present updates of their distribution, reliable censuses to estimate population sizes, population growth rate, population structure, longevity, reproductive success and frequency of herbivory. Recent surveys and careful censuses revealed that the four taxa exclusively restricted to rocky habitats (Borderea chouardii, Androsace pyrenaica, Petrocoptis pseudoviscosa, Petrocoptis montsicciana) have more populations and/or individuals than previously thought. The remaining species, an orchid (Cypripedium calceolus), showed an important decline in population number. So while the rupicolous taxa might be considered naturally rare, the orchid is becoming rare. We failed to find evidence of current poor performance within populations, as recruitment was detected, population growth rate was quite stable in recent years, fruit and seed set was apparently adequate, and herbivory and predation were absent or very low. Additionally, most of the species show a long life span, which might buffer them against demographic and environmental stochasticity in absence of human disturbance. 相似文献
15.
Although conservation and restoration practitioners have focused on maximizing aboveground population size and seed set of rare plants, a clear understanding of seed bank dynamics is crucial to managing these species. Santa Cruz tarplant (Holocarpha macradenia) is a threatened annual forb restricted to coastal prairie habitats in central California. Holocarpha produces disk achenes germinating within a year of production and ray achenes forming a persistent seed bank. We constructed both deterministic and stochastic demographic models for a restored Holocarpha population, using demographic rates measured separately for unmanipulated plants and plants growing in plots where vegetation was clipped. The deterministic models indicated that regardless of germination from the seed bank, the population would decline without clipping or similar treatments that enhance survival and reproductive output. Deterministic models showed only a slight positive effect of increased ray seed germination rates on population growth, which would need to be balanced against a potential loss of buffering against environmental variation as the dormant seed bank was reduced. Our stochastic simulations suggested that extinction risk for Holocarpha populations would be minimized by intermediate levels of ray seed germination. Thus, managers should focus on improving the performance of aboveground plants before considering actions to stimulate germination, since the former will yield a greater increase in deterministic population growth and not sacrifice any buffering effect of the seed bank. This case study emphasizes the importance of considering dormant seeds and seed banks in designing successful restoration and management strategies for plant species at risk of extinction. 相似文献
16.
《Communications in Soil Science and Plant Analysis》2012,43(15-16):2013-2027
Abstract The effects of three levels of salinity [0, 50, and 100 mM of sodium chloride (NaCl)] and the addition of potassium, calcium, nitrogen, phosphorus, iron, manganese, and boron (K, Ca, N, P, Fe, Mn, and B) on seed germination and survival of Helianthus annuus L. plants grown in an inert medium were studied. Increasing levels of salinity significantly decreased germination percentage. The presence of NaCl affected seedling survival rather than germination. Nitrogen addition damaged seedling growth, especially in high saline conditions. Addition of some nutrients may alleviate the effects induced by NaCl. Calcium additions to the culture medium significantly improved germination percentage and seedling survival, which markedly decreased after addition of K and B under saline conditions. Iron addition, especially in the ferrous form, counteracted the effects of salinity on seed germination and seedling survival. Phosphorus addition showed detrimental effects on germination and especially in seedling survival; however, it benefited the surviving seedling's growth. 相似文献
17.
Nyambayar Dashzeveg Barbara Vornam Soninkhishig Nergui Andreas Buerkert 《Genetic Resources and Crop Evolution》2018,65(7):1857-1865
Glycyrrhiza uralensis Fisch. ex DC. (Chinese licorice) is an important medicinal plant in Mongolia. Despite its traditional role in local healing systems, little is known about the existing intra-specific diversity of this species. The aim of the present study therefore was to analyze morphological and genetic diversities of G. uralensis in the Bulgan River Basin in Western Mongolia and to test different treatments aimed at breaking seed dormancy in order to facilitate effective cultivation of this species. Morphological measurements were taken and leaf and seed samples were collected in eight populations of the Bulgan River Basin. Subsequently, DNA was extracted from leaves and analyzed employing amplified fragment length polymorphisms. A total of 11 treatments were used to test and enhance seed germination. Morphological characteristics differed among populations. Treatments used in the study affected total emergence and mean days to germination of the seeds differently, but populations did not differ in their response whereas differentiation within populations was high. Mechanical and acid scarifications were more effective compared to other treatments. The level of genetic diversity in the studied populations was lower than the average value of the short-lived perennial herbs, but close to that of the self-breeding species. Most of the genetic variation was within populations. Chinese licorice is suitable for cultivation in the Bulgan River Basin and effective scarification can increase germination of seeds across the populations collected in our study area. 相似文献
18.
Pinus gerardiana Wall. is an important nut-producing pine having restricted distribution in the world. It has been observed that natural regeneration in the species is extremely poor or entirely lacking. The species has erratic and infrequent seed years, dormancy-related problems, and slow growth of seedling, which reduces its regeneration process in natural habitats. Therefore, we investigated the effect of growing medium and seed size on germination and seedling growth of the Pinus gerardiana. The seeds were categorized into two sizes, viz, small (<2.35 cm) and large (>2.35 cm) and five growing medium treatments were used, viz, Soil:Sand:FYM; Soil:Sand:Moss:FYM; Soil:Moss:Vermicompost; Soil:Sand:Vermicompost; and Soil:Sand:Moss:Vermicompost, for assessing their impact on germination and seedling growth. It was observed that, among different growing medium treatments, higher germination and seedling growth parameters were recorded, when Soil:Sand:Moss:Vermicompost was used for the study. Between different seed sizes, higher germination and seedling growth were recorded when seed size was large. 相似文献
19.
Yvonne Herrerías-Diego Kathryn E. Stoner Yared Hernández-Flores 《Biological conservation》2008,141(1):241-248
Forests fragmentation reduces the density of natural plant populations forming patches of the remaining individuals. One of the biotic interactions that can be affected by forest fragmentation and is poorly studied is seed predation. We determined the effects of forest fragmentation on seed and fruit predation in Ceiba aesculifolia by comparing trees in continuous forest with trees in fragmented forest. We compared the following variables: (a) frequency of fruit predation by Collie’s squirrel (Sciurus colliaei) in each habitat; (b) frequency of the cotton-staining bug seed predator (Dysdercus, Orden Hemiptera) in each habitat; (c) the effect of seed predation on germination frequency and time; and (d) the effect of different life stages of Dysdercus on seed viability. In continuous habitat, 100% of the trees presented fruits with squirrel predation while only 34% of trees in fragmented habitats presented fruit predation. In continuous forest 27% of the trees contained fruits with the seed predator Dysdercus, while only 2% of the trees in fragmented forest presented Dysdercus. The initial weight of damaged seeds was greater than seeds that were not damaged indicating that seed predators select heavier seeds to feed upon. Frequency of seed germination was affected by different life stages; pre-adults decreased germination significantly more than nymphs and adults. Seed predation significantly increased the time it took for germination to occur. Our study shows that forest fragmentation significantly affects predation patterns of squirrels and cotton-staining bugs. Reduction of natural seed predators in forest fragments may have long-term consequences on forest structure and diversity. 相似文献
20.
Yanhong Xu Federico Rossi Giovanni Colica Songqiang Deng Roberto De Philippis Lanzhou Chen 《Biology and Fertility of Soils》2013,49(2):143-152
The importance of cyanobacterial polysaccharides of biological soil crusts in sand surface stabilization and soil nutrient retention has been long acknowledged. However, the role of cyanobacterial polysaccharides as a source of nutrition to vascular plants in crusted areas is ignored. In this study, the chemical composition of the polysaccharide synthesized by Phormidium tenue and the effects of its presence on seed germination and seedling metabolism of the shrub Caragana korshinskii were investigated. The crude polysaccharide synthesized by P. tenue was composed of 15 % protein and 58 % carbohydrate and showed the presence of 12 different types of monosaccharides. The addition of the polysaccharide significantly (P?<?0.05) increased seed germination and metabolic activity of the seedling of the shrub C. korshinskii. The optimal concentration for vigor index, root length, root vigor, and total N and P contents was 10 mg/L polysaccharide; for the germination rate, nitrate reductase activity, carbohydrate content, chlorophyll, and Mg2+ content, the optimal was 60 mg/L polysaccharide, while for K+ and Ca2+ contents, photosynthetic efficiency and superoxide dismutase activity was 120 mg/L. The presence of the polysaccharide increased seed germination rate, ion uptake, and photosynthetic activity by affecting the electron transport chain and decreased oxidative damage by eliminating reactive oxygen species in C. korshinskii, thus promoting shrub performance in crusted desert areas. 相似文献