Factors influencing seed germination of Cyperus capitatus, inhabiting the moving sand dunes in southern Europe

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.     

Critical conditions for successful regeneration of an endangered annual plant,Cryptantha minima: A modeling approach

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.     

Pre- and post-dispersal seed loss and soil seed dynamics of the dominant Bulnesia retama (Zygophyllaceae) shrub in a sandy Monte desert of western Argentina

In deserts and semi-deserts dominant plants seldom rely on a persistent seed bank to ensure their recruitment from sexual reproduction, which is generally based on the seeds produced in the last reproductive event. We studied pre- and post-dispersal seed loss of Bulnesia retama, a dominant shrub of the sandy Monte deserts (western Argentina). We hypothesised that pre- and post-dispersal seed depletion in B. retama regulate soil seed density and in turn decrease soil seed reserves. We also hypothesised that spatial patches induced by standing vegetation and other microsites additionally affect post-dispersal seed loss and soil seed density.We observed that as much as half the total seed production was lost due to pre-dispersal seed predation. Seed dispersal plus predation showed a negative exponential function with 61% of seeds falling during the first 28 days, and 99% after 90 days, when 34% of the seeds remained inside excluded branches. A significant patch effect was observed on soil seed density and seed dynamics, with a greater number of seeds and increased seed depletion rates below B. retama shrubs. However, spatial patches did not affect seed germination although they increased with burial time, from 22% to 70% after 75 and 276 days, respectively. Likewise, a similar trend was found in potential seed germination; seeds collected directly from mother plants had a low germination rate (less than 25%), which increased to 75% after 276 days of soil burial. About 15% of the dispersed seeds should persist to the next rainy season, thus contributing to a low-density but persistent seed bank.The delay in seed germination and temporal decrease in soil seed density that we observed for B. retama suggest that a set of mechanisms have been developed promoting germination events whenever soil water is available, at any moment of the year.     

Seed biology of Australian arid zone species: Germination of 18 species used for rehabilitation

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.     

Comparative study of seed germination and growth of Kochia prostrata and Kochia scoparia (Chenopodiaceae) under salinity

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.     

Seed germination of five Helianthemum species: Effect of temperature and presowing treatments

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.     

Factors controlling regeneration in a rare desert tree Acacia peuce: Limits to soil seed bank accumulation in time and space

We assessed reasons for rare recruitment in Acacia peuce, an Australian arid zone tree, by testing recruitment-limitation hypotheses relating to seed bank inputs and losses. Viable seed occurred in low density in the soil (<1 seed m²) whereas freshly produced seed was non-dormant and germination was high and fast, indicating small rain events can deplete seed banks without providing sufficient moisture for seedling survival. Seed bank seed had lower viability than fresh seed. Insect predation of seed was negligible but seed pod production and seed number/pod were low. Thus, seed bank accumulation is limited by low inputs and continual high seed losses through germination and potentially seed death. No seed shadow effect under adult canopies was found, but dispersal beyond existing stands was negligible. Seed dispersal from parent plants occurred by wind movement of unopened pods whereas the resident ant fauna did not transport seed. Microsite parameters strongly influenced horizontal distribution of buried seed, with all seed being retrieved from vegetated sandy mounds. Overall, we found that seedling recruitment is likely to be confined to large above average rainfall events because the species is unlikely to maintain a seed bank in below-average and average rainfall phases.     

Seedling recruitment in a semi-arid steppe: The role of microsite and post-dispersal seed predation

Grasslands dominated by Stipa tenacissima are important ecosystems in the arid and semiarid climates of western Mediterranean, where they have originated by degradation of open dry forests and shrublands. At present, although the level of exploitation in these ecosystems is very low, succession processes seem to have stopped. In this study, we explore the role of microsite and post-dispersal seed predation on the seedling emergence of two species from advanced successional stages (Rhamnus lycioides, Quercus coccifera), three species from degraded stages (Cistus clusii, Helianthemum violaceum, Anthyllis terniflora), and of the dominant species (Stipa tenacissima). Seeds of these species were sown in plots divided into two microsites: (i) under tussocks of S. tenacissima and (ii) in the bare soil between tussocks. Soil moisture was significantly higher in the tussock microsites. The interaction observed between microsite and time, reflected the slower drying process under tussocks. Seed predation was in general high and differed significantly between species but not between microsites. Q. coccifera was especially affected by predation. The only germination detected in gap areas was that of H. violaceum. The results pointed to a direct facilitative effect of tussock grass on the germination in R. lycioides (20.4±8.0%) and S. tenacissima (41.3±5.7%) while the corresponding figures for bare ground were 0%. These results suggest that the recovery of potential vegetation in this ecosystem is not possible or, at least, is very slow because the residual shrub patches do not generate a sufficient number of seeds able to disperse to favorable germination microsites. S. tenacissima may act as facilitator of seedling recruitment if there is a supply of diaspores.     

Passage time, viability, and germination of seeds ingested by foxes

Seed passage through the gut of vertebrates is critical for endozoochorus seed dispersal because it may influence seed viability and germination capacity. Foxes are important fruit-eaters and presumed seed dispersers in the Chaco ecoregion. We experimentally assessed the seed passage time (SPT) and its effect on seed viability and germination in two fox species (Pseudalopex gymnocercus and Cerdocyon thous) that occur in the Chaco. Passage time was measured using both artificial seeds of three sizes and wild seeds of four native fleshy-fruit species commonly consumed by foxes (Ziziphus mistol, Acacia aroma, Celtis tala, and Syagrus romanzoffiana). The average SPT was 6.8 h for the Pampa fox and 7.7 h for the crab-eating fox. Passage time did not differ either among seeds of different sizes or between fox species. Passage through digestive tract of both fox species did not affect seed survival, whereas germination rate was slightly improved. Our data suggest that both fox species are legitimate seed dispersers of the four species studied, having a positive effect on both germination rate and dispersal distance from the parent plant.     

Environmental control of seed dormancy and germination in the short-lived Olimarabidopsis pumila (Brassicaceae)

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.     

Effect of environmental heterogeneity on field germination of Opuntia tomentosa (Cactaceae,Opuntioideae) seeds

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.     

Disentangling Fabiana imbricata (Solanaceae) regeneration: The importance of disturbance and rainfall

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.     

Soil seed bank longevity of the exotic annual grass Bromus rubens in the Mojave Desert,USA

Although arid environments are often considered among the least invaded terrestrial biomes, the impacts of exotic plant species can be severe and long lasting. Bromus rubens (red brome) is an exotic annual grass species in the Mojave Desert known to outcompete native plant species, alter habitat, and promote accumulation of fuel that contributes to increasing fire frequency and severity. We assessed longevity of the exotic B. rubens seeds in the soil by burying seeds at four depths (0, 2, 5, and 10 cm) and recovering seeds 6, 12, 18, and 24 months after burial. Seed viability was reduced with greater burial depth and greater time since burial. A relatively small proportion of seeds retained viability for two years, suggesting that while the B. rubens seed bank can be large, it is relatively short-lived. Although B. rubens apparently relies more on the annual production, dispersal, and germination of seeds than on a long-lived seed bank for its annual recruitment, the numerous seeds produced by individual plants indicate that even a small proportion of seeds remaining viable for more than a year can aid recruitment from the seed bank and is an important factor in understanding population dynamics.     

Seed germination responses of Periploca sepium Bunge, a dominant shrub in the Loess hilly regions of China

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.     

Effects of seed beetles on the performance of desert legumes depend on host species,plant stage,and beetle density

Seeds of many arid habitat plants have a water-impermeable coat and can germinate only after being scarified. Bruchine seed beetles are important parasites of legume seeds in these environments, but their effect on germination can be unpredictable. Beetles deplete seed resources and can kill the embryo but also scarify seeds. We investigated the effects of a generalist parasite, Stator limbatus, on the germination and growth of two common legumes in the Sonoran desert, catclaw acacia (Acacia greggii) and blue paloverde (Parkinsonia florida). Feeding damage from a single larva greatly increased germination of paloverde but not acacia. This benefit was reduced if seeds were attacked by multiple larvae. Beetle-damaged seeds of both hosts germinated more quickly than did control seeds. Infestation by beetles reduced seedling size, though effects were greater for paloverde than for acacia. Our results demonstrate that the effect of S. limbatus can be highly host-specific. In addition, beetle infestation may enhance or reduce seedling recruitment, depending on the availability of other scarifying agents and the number of larvae per seed. Such contingencies make it difficult to predict the net effect of seed beetles on efforts to control invasive legume hosts or establish native hosts during aridland restoration.     

Seed germination of wild,in situ-managed,and cultivated populations of columnar cacti in the Tehuacán-Cuicatlán Valley,Mexico

Seed germination was compared among wild, in situ-managed (wild plants let standing in areas cleared for agriculture), and cultivated populations of the columnar cacti Stenocereus pruinosus, Polaskia chichipe, Myrtillocactus schenckii, and Polaskia chende, species representing a gradient from higher to lower management intensity, respectively. We hypothesized that seeds from cultivated populations have higher water requirements to germinate than seeds of other populations, and that such difference is stronger in species more intensely managed. Germination was evaluated under water potential treatments at 0.0, ?0.2, and ?0.4 MPa. Interspecific differences were identified; germination rates markedly decreased in S. pruinosus and P. chichipe as water potential reduced. M. schenckii seeds germinated better at ?0.2 MPa, and seeds of P. chende in all treatments. Seed germination of wild and cultivated populations was similar in all cases and, therefore, at the population level domestication does not appear to have influenced variations in germination of the studied cacti species. However, experiments to test whether germination of seeds from plants with clear signs of domestication differs with seeds from other plants and their differential germination and seedling survival in wild, in situ-managed and cultivated environments could help to precise the influence of domestication on these plants.     

Benefits of mycorrhizal inoculation in reintroduction of endangered plant species under drought conditions

Numerous human activities constitute threats to biodiversity. The effects of climate change, including increasing drought in already arid lands, pose an additional layer of uncertainty in the fate of rare species. In the case of plants, reintroduction is becoming an important active management practice in species conservation. We hypothesized that even under extreme drought inoculation with mycorrhizal fungi would increase growth rates of an endangered plant in experimental reintroduction. We selected a plant species, Abronia macrocarpa, and conducted the experiment in Texas while the area was experiencing mild and extreme drought intensities. Treatment plots were planted with seed inoculated with arbuscular mycorrhizal fungi and control plots were planted with seed coated with autoclaved inoculant. We analyzed measurements of growth and development of germinated plants. Mean number of leaves was greater in treatment plants (P = 0.005) and mean aerial diameter was larger in treatment plants (P = 0.02) than in control plants. Significantly improved growth suggests that inoculation is a viable technique to increase reintroduction success in plant species especially during periods of drought.     

Germination of Callitris seeds in relation to temperature, water stress, priming, and hydration–dehydration cycles

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.     

荒漠植物种子萌发研究进展

 对种子自身结构,水分、温度、光照、沙埋深度等对荒漠植物种子萌发的影响进行了综述。硬实种子的不透水性、不透气性以及物理障碍是影响种子萌发的重要因素,通过热水浸种、擦破种皮或果皮、浓硫酸浸泡、低温或辐射处理可以破除硬实的影响。有些荒漠植物果皮或种皮外包有粘液层,这种结构对种子的萌发及幼苗生长有促进作用;部分植物的种胚覆盖物含有生长抑制物质而抑制种子萌发;胚休眠与后熟是影响胚萌发的重要生理因素。雨量大小、分布,降雨次数及土壤湿度是决定荒漠植物种子萌发的重要生态因子;温度影响种子的萌发,变温促进萌发;部分荒漠植物种子的萌发需要光照,有些要在暗中萌发,有些则对光无特异的需求;沙埋深度可调节光照、土壤湿度和土壤温度,从而调节种子萌发。应重视荒漠植物种子对严酷环境适应的研究,从分子水平上阐述其对严酷生境的适应机制。     

Heliotropium europaeum only germinates following sufficient rainfall to allow reproduction

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.