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1.
Soils of arid regions of Central Asia contain salts of different types that may differentially affect seed germination and plant development. We studied effect of NaCl, Na2SO4, 2NaCl + KCl + CaCl2 and 2Na2SO4+K2SO4+MgSO4 on germination of Kochia prostrata and Kochia scoparia seeds under a range of concentrations from 0.5 to 5% and at two constant temperature regimes +22 °C and +6 °C. The observed salt tolerance limit of germination at constant temperature +22 °C for both species was 5-6%, while at low temperature (+6 °C) this limit was 2%. The salt tolerance of young plants (before flowering) was 3% for NaCl. Low concentrations of sulfuric and mixed salts had a stimulating effect on seed germination in K. prostrata. Despite similarity of salt-tolerance limits the studied species showed a significant difference in seed recovery ability, i.e. the ability of ungerminated, salt-soaked seeds to germinate after transfer to fresh water. K. scoparia demonstrated a full germination recovery after seed transfer to distilled water while K. prostrata showed only a partial recovery.  相似文献   

2.
Populations of the winter annual Eruca sativa in Israel are distributed along a climatic gradient, from Mediterranean mesic habitats in the north to semi-arid and arid habitats in the south. Seed cohorts of five populations sampled across the gradient were produced in a common-garden experiment, and their germination was tested under continuous light or darkness at 5–35 °C, as well as with alternating 30/20 and 25/15 °C temperatures under a 12/12 h photoperiod. Germination was enhanced by light and by increasing temperature. Under constant temperatures maximal germination of arid and semi-arid populations was lower than in the mesic populations, suggesting on higher levels of primary dormancy with increasing aridity. Seeds that did not germinate in darkness or at low temperatures in light, germinated almost fully when exposed to GA3 at 25 °C, indicating that imbibition under less favorable conditions induces secondary dormancy in E. sativa. Daily alternating temperatures did not affect or even reduced seed germination compared to constant 25 and 30 °C in continuous light. Exposure of dry seeds to 30 °C before imbibition increased germination to ≥80% in seed cohorts of all populations. These responses to light and temperature indicate that adaptation of E. sativa to the Mediterranean environment is associated with the ability to germinate under the relatively warm autumn temperatures, and is enhanced by exposure to high temperature during the dry summer.  相似文献   

3.
Experiments were conducted to determine the effects of temperature, light, osmotic stress, hydration-dehydration regime and stress relief on the seed germination of Periploca sepium Bunge (Chinese silk vine Asclepiadaceae), which is a native shrub in the Loess Plateau of Northwest China. Freshly harvested seeds germinated equally well in both light and darkness. Seeds germinated under all of tested temperature regimes, and much faster when temperature was maintained at 30, 35, and 30/20, 30/25, 35/25, 35/30 °C range, with more than 90% of seeds germinating within 2 days. Moderate osmotic stress did not inhibit germination at any tested temperature. At 30 °C, seed germination was not affected significantly above −0.8 MPa. The hydration-dehydration pretreatment showed none side effects on P. sepium seeds and the seeds germinated more rapidly as soon as optimal water condition was restored. These results show the advantages of P. sepium, which is a competitive and widespread shrub in dry areas, and provide useful information for vegetation restoration in these drought-prone regions.  相似文献   

4.
In Mediterranean ecosystems, fire influences plant population dynamics and changes plant community structure by affecting germination and establishment of seeder shrubs. Fabiana imbricata is a long-lived seeder shrub with a broad distribution in South America. In Northwestern Patagonia grasslands there are many records of F. imbricata recruitment after fires. We hypothesized that recruitment is promoted by: 1) soil erosion that exposes deeply buried seeds; 2) direct fire effects such as heat that could break seed dormancy; 3) indirect fire effects (i.e. increase of light availability and elimination of allelopathic substances) and 4) water availability in spring. In field conditions, we tested the effects of shading and soil disturbance on F. imbricata recruitment and seed availability and distribution in the soil profile. Under controlled conditions, we investigated the influence of leaf leachate, light, heat and water on seed germination and seedling emergence. Seed germination was inhibited by leachate, and seedling emergence was inhibited by seed heated to 80 °C and 120° for 5 min. F. imbricata seedlings only emerged in germination treatments that simulated wet and very wet spring conditions. Fire and postfire wind that favor seed exposure, combined with high precipitation early in the growing season, would be necessary for successful shrub recruitment. When F. imbricata shrubland colonizes the grassland, it strongly modifies local vegetation structure, reduces species richness and increases fuel loads. F. imbricata is a key species in the ecosystem specially related to fire regime. Information on the postfire regeneration of this species would provide valuable knowledge of the changes in biomass accumulation in a fire-prone Mediterranean ecosystem.  相似文献   

5.
Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination.  相似文献   

6.
Tiny cryptanthe (Cryptantha minima Rydb.) is an endangered annual plant adapted to prairie sand dunes of Canada. Thermal time and hydrothermal time models were used to quantify the effect of temperature and water potential on seed germination and to relate it to field conditions. Tiny cryptanthe seeds had a base temperature of ?3.9 °C for germination. Final germination percentage was highest at temperatures near the freezing point. Seeds required approximately 130.6 °C d to reach 50% germination under optimal water conditions. Seed germination was sensitive to water stress and large seeds had lower germination than small ones especially at reduced water potentials and higher temperatures. The high potential germination and low seed dormancy indicate that tiny cryptanthe lacks a dormancy mechanism, but the unique germination response to temperature enables it to fully utilize water from spring snowmelt before drought in the summer. Future climate change with higher temperatures could reduce regeneration success of this species unless there is an associated increase in winter and spring precipitation.  相似文献   

7.
The germination behaviour of five Helianthemum species (H. almeriense, H. appeninum, H. cinereum, H. hirtum, H. squamatum) has been studied under controlled conditions. Constant 15, 20 or 25 °C and alternating 25/15 °C temperature regimes and 16/8 h light/dark photoperiod conditions were used. Presowing treatments applied were manual scarification, boiling water, hot water, dry heat and sulphuric acid. Germination values recorded were final germination percentage and germination rate expressed as days to reach 50% of the final germination percentage (T50). Incubation temperature had no significant effect on final germination percentage for untreated seeds of the five Helianthemum species. However, variation due to temperature was significant for scarified seeds, with the lowest germination percentage attained at 25 °C. In all Helianthemum species studied, the highest germination percentages were obtained by manual scarification of seeds. Germination rate of scarified seeds decreased as germination temperature increased. The different presowing treatments investigated allowed some germination in some species, but none were any better than manual scarification. The high germination among most species studied, following mechanical rupture of the seed coat, shows that the mechanism of dormancy lies in the seed coat. The physical dormancy caused by impermeable seed-coat appears to be the main reason of poor germination of untreated seeds of Helianthemum species studied.  相似文献   

8.
Seeds ofAcacia origena,A. pilispinaandPterolobium stellatumhave a hard seed coat that hampers imbibition of water and prevents maximum, uniform and rapid germination. Therefore, the seeds were subjected to different treatments involving mechanical scarification, concentrated sulphuric acid and boiling water to break the dormancy imposed by the hard seed coat. To determine the effects of different constant temperature regimes on germination, scarified seeds were incubated on a thermogradient at 10, 15, 20, 25 and 30°C. Germination of scarified seeds was also tested in light and dark. Mechanical scarification resulted in 100% germination for theAcaciaspecies and 94% forP. stellatum. ForA. origena, sulphuric acid treatments for 60, 90 and 120 min resulted in significantly higher per cent germination (>95%) than all the other treatments. ForA. pilispina, sulphuric acid treatments for 45 and 60 min, as well as immersing seeds for 1 min in hot water, gave significantly higher per cent germination (97%) than all the other treatments. ForP. stellatum, mechanical scarification and all the acid treatments applied resulted in significantly higher per cent germination (>85%) than the control and all hot water treatments. All seeds ofP. stellatumimmersed in hot water, even for 1 min, rotted soon after sowing, indicating that they are sensitive to high temperatures. Scarified seeds of the twoAcaciaspecies germinated to a higher degree (≥90%) between 10 and 30°C, while germination of scarified seeds ofP. stellatumranged from 48 to 82% between 10 and 30°C. Scarified seeds of the three species germinated to a large extent (>70%) both in light and dark, indicating that seeds do not require light for germination.  相似文献   

9.
This paper presents data on the germination traits of five perennials (Allium polyrrhizum, Agropyron cristatum, Arenaria meyeri, Artemisia frigida and Artemisia santolinifolia) widespread in the mountain steppes of southern Mongolia. Germination and seed viability were assessed at three alternate temperatures (8/4 °C, 20/10 °C, 32/20 °C), three levels of osmotic stress (deionized water; −0.5 MPa, −1 MPa Mannitol solution), and under conditions of alternate light/darkness versus complete darkness. The results of a factorial ANOVA with treatments and species as main effects showed that all five species germinated best at higher temperatures, with only Agropyron cristatum showing some seed mortality. Osmotic stress reduced seed viability and total germination in all five species. Darkness had no influence on viability, but positively affected seed germination of Allium polyrrhizum and Agropyron cristatum. We therefore conclude that, in the field, germination of all five species is mainly controlled by ambient temperatures and water availability, both of which drop towards the end of summer when dispersal takes place and effectively delay seedling recruitment until the next vegetation period.  相似文献   

10.
Regions with Mediterranean climates are seasonally arid and provide a niche for ephemeral species which germinate following discrete and variable rainfall during summer. These species must be able to detect when conditions are suitable for completion of their life cycle. Common heliotrope (Heliotropium europaeum) is one such species. It is considered a weed in its naturalised habitat in southern Australia as it uses resources that could be used by ensuing crops, and is toxic to livestock.We examined common heliotrope's germination responses to temperature and water potential, the effect of simulated rainfall on seedling emergence and plant growth in lysimeters.Fresh seeds of common heliotrope have relatively high optimum temperatures and water potentials for germination (around 35 °C and 0 MPa). Germination percentage of seeds extracted from the soil seed bank varies seasonally. In the soil types and climate of the study area, 24.2 mm is the minimum amount of rainfall resulting in emergence. Evapotranspiration required to reach minimal reproductive output was 19.4 mm.Common heliotrope's germination requirements have been selected to ensure that it will only germinate after sufficient rainfall to allow reproductive output. This is the mechanism through which common heliotrope detects its temporal niche.  相似文献   

11.
The purpose of our study was to better understand seed germination ecology of the spring annual short-lived Olimarabidopsis pumila, which grows in the Gurbantonggut Desert, China. Seeds underwent after-ripening at 4, 20 ± 2 (room temperature) and 30 °C. After dormancy was broken, germination capacity was a function of temperature and presence of light. For the temperature range studied (4–30 °C), germination capacity was significantly higher between 15 and 25 °C than at temperatures above or below them. Alternating temperatures of 20/10, 25/10 and 25/15 °C were favorable for germination. Although GA3 did promote dark germination of seeds, GA3 did not replace light for germination. Seeds germinated to >75% if light exposure time was over 8 h and temperature and moisture conditions were favorable. Seeds were able to germinate at relatively low water potentials (83% at ?0.41 MPa), but decreasing water potentials produced detrimental effects on germination percentage and rate. Thus, dormancy characteristics and germination behavior of O. pumila seeds ensure that germination occurs in the desert only when soil moisture conditions are favorable for seedling establishment and survival.  相似文献   

12.
We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments.  相似文献   

13.
旱雀麦(Bromus tectorum)原产于欧亚大陆,18世纪传入北美,并成为该地区的入侵植物。然而,同为雀麦属的扁穗雀麦(Bromus catharticus)和无芒雀麦(Bromus inermis)并不具有旱雀麦的入侵性。本研究设置高温、低温和黑暗等处理,探讨温度和光照对3种植物种子萌发的影响,旨在从种子萌发的角度揭示旱雀麦的入侵性。结果表明：温度和光照对旱雀麦和扁穗雀麦种子的发芽率均无明显影响(p>0.05);高温和黑暗处理显著提高了无芒雀麦种子的发芽率(p<0.05),对旱雀麦、扁穗雀麦和无芒雀麦种子的发芽势、发芽指数、日均发芽率、发芽系数、发芽峰值和发芽值有一定的促进作用,而低温处理则表现出相反的效应;高温和黑暗处理对3种植物种子的平均发芽天数和萌发持续时间有一定降低的作用,而低温处理则表现出相反的效应。同一处理下旱雀麦种子萌发各项指标均优于另两种植物,这可能是旱雀麦具有较强入侵性的重要原因。  相似文献   

14.
In semi-arid environments plants should be selected to germinate at times most suitable for seedling establishment. Germinability, rate of germination and temperature preference for germination (12 or 28°C constant) were analysed with respect to growth form (grass, forb, woody), longevity and seed size. Short-lived species showed preferential germination at either high or low temperature, whereas long-lived species tended to be indifferent to season. Germinability was >20% for 28 spp., 17 species were <10% and 21 species did not germinate under any circumstances. Growth form or life-span did not influence germination. Woody species germinated rapidly. Germinability and germination rate were positively associated.  相似文献   

15.
We studied in Opuntia tomentosa the effect of plant shade (orientation and distance), and the place where the seeds remained before germination. Seeds were collected in 1998 and a) sown immediately on soil (non-buried seeds), b) stored in the laboratory and sown on soil during the 1999 rainy season (control) or c) buried after collection (under the shade of a tree, a rock and in an open space), exhumed 7 months later and sown in 1999 (exhumed seeds). Seeds were sown under or outside the shade of several trees; or on the northern, eastern and western sides of a 14-m-tall tree. In 1999, germination was high in all samples, but the control seeds had delayed germination. After two rainy seasons, non-buried seeds had the lowest germination rate. Germination was not affected by the distance from the tree. Outside of the plant's shade, germination was low. Germination was affected more by the environmental heterogeneity than by the individual plant shade. Germination probabilities were the highest at 16–19 °C; field germination was zero at 20.6 °C. Seed polymorphism and microenvironmental heterogeneity spread germination across two rainy seasons creating a permanent seed bank.  相似文献   

16.
Colonization processes in semi-arid Mediterranean old-fields   总被引：3，自引：0，他引：3  
Semi-arid Mediterranean ecosystems undergo a slow process of secondary succession after disturbance which is dependent on rainfall. We tested the hypothesis that colonization of abandoned lands in semi-arid SE Spain was slowed down by seed dispersal and species-specific responses to climatic variability. In field and glasshouse experiments we analysed germination of the two main colonizer species, their appearance in the field as seedlings, their relationships with climate and the resulting population structure. Seed germination of the two dominant legume species, Anthyllis cytisoides and Retama sphaerocarpa, was enhanced by scarification, but triggered in the field by temperature and rainfall, respectively. There was no evidence of allelopathic effects affecting germination in the field. Population structure reflected high inter-annual variability in shrub establishment, which was related to rainfall in spite of self-thinning and other processes that modeled current shrub numbers. Colonization of abandoned lands in semi-arid, Mediterranean environments in SE Spain seems to be primarily limited by seed dispersal, but also affected by climatic variability, which produced temporally separated recruitment events.  相似文献   

17.
The effects of temperature, water stress, hydration–dehydration cycles and seed priming on the germination of Callitris verrucosa and Callitris preissii, two Australian semi-arid coniferous tree species, were investigated. Optimum germination occurred at 18°C, with a minimum germination time of 8–9 days for both species. At this temperature, germination was inhibited at osmotic potentials lower than −1·0 MPa, but the capacity to germinate at low osmotic stress increased as the temperature decreased. Seed priming and hydration–dehydration cycles did not reduce seed viability, and Callitris seeds appear to retain the physiological changes induced by short-term hydration, as the time to the onset of germination was decreased to about 3 days. The capacity of Callitris seeds for incremental germination is likely to increase overall germination success in a low rainfall environment.  相似文献   

18.
We investigated the effects of soil water potential (SWP) and temperature on seed germination of six coexisting species of an inter-tropical desert. These species include three life-forms; the shrubs Cercidium praecox andProsopis laevigata ; the columnar succulents Neobuxbaumia tetetzo and Pachycereus hollianus; and the arborescent semi-succulents Beaucarnea gracilis and Yucca periculosa. In the six species germinability increased and germination time and speed of germination (t50) decreased as SWP decreased. The SWP treatments were 0 MPa, −0·12 MPa, −0·2 MPa, −0·41 MPa and −0·66 MPa. There was, however, a SWP threshold below which germination time and t50increased and germinability decreased. The shrubs had the highest germinability whereas the columnar succulents had the lowest. The shrubs also had shorter germination time andt50 than arborescent semi-succulents whereas seeds of the columnar succulents were indeterminate. In all species except P. laevigata germinability increased and the germination time and t50decreased as temperature increased. The temperature treatments were 12°C, 20°C and 26°C. The shrubs had the shortest t50and germination time and the highest germinability at all temperatures. Arborescent semi-succulents had the lowest germinability and longest germination time and t50at the three temperatures treatments. Our results support the hypothesis that in desert environments different plant life-forms utilise different germination strategies to persist.  相似文献   

19.
We report on the phenology, seed production, and three assays (field, greenhouse and laboratory) to detect the optimal temperature for germination (OPT) and the temperature with fastest germination rate (TFASG) of seven Mimosa species, all endemic to Mexico: Mimosa adenantheroides (M. Martens and Galeotti) Benth., M. calcicola B. L. Rob., M. lacerata Rose, M. luisana Brandegee, M polyantha Benth., M. purpusii Brandegee and M. texana (A. Gray) Small var. filipes (Britton and Rose) Barneby. Flowering and fruiting take place during the wet season (May–September). Though flowering periods overlap among species, no hybrid species were found. The reproductive strategy includes a large number of seeds produced (4000–15000 per plant); however, a high percentage (30–75%) is not viable due to bruchid predation (Acanthoscelides mexicanus (Sharp) and Stator pruininus Horn). In the laboratory, OPT was established at (23°C)24°C(27–28°C) and TFASG at (20°C)25°C(30°C), with 100% of germination in six of the seven Mimosa species. In the field, the maximum germination rate (MAXG) was 92% to 100%, whereas in the greenhouse this value was 56% to 80%. Our results show that heat and moisture do not necessarily stress Mimosa seedling germination, but shade seems to be an important factor influencing germination.  相似文献   

20.
Revegetation of disturbed land, particularly in arid environments, is often hindered by low seedling establishment. Information on seed biology and germination cues of keystone species is lacking, particularly in arid Australia; a major zone for mining developments. This study investigated seed characteristics and germination of 18 common species required for rehabilitation of disturbed areas at Shark Bay Salt in the Shark Bay World Heritage Area, Western Australia. Untreated seeds of seven species (Aphanopetalum clematideum, Atriplex bunburyana, Austrostipa elegantissima, Melaleuca cardiophylla, Pembertonia latisquamea, Rhagodia baccata, Salsola tragus) exhibited high germination percentages. Seeds of two species (Acacia tetragonophylla, Stylobasium spathulatum) had low imbibition, which increased with hot-water treatment, hence require scarification for germination. Gibberellic acid, smoke water and karrikinolide (a butenolide isolated from smoke) substantially increased germination percentages of three species (Anthocercis littorea, Diplolaena grandiflora, Solanum orbiculatum). Seeds of the remaining six species (Dioscorea hastifolia, Eremophila oldfieldii, Nitraria billardierei, Ptilotus exaltatus, Thryptomene baeckeacea, Zygophyllum fruticulosum) had low germination percentages regardless of treatment. Most species germinated equally well at 26/13 °C and 33/18 °C, however seven species had improved performance at 26/13 °C. This study is significant to land managers and conservation agencies with an interest in optimising germination of arid zone seeds for restoration.  相似文献   

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