The effect of extended exposure to hypersaline conditions on the germination of five inland halophyte species

In order to determine how salinity and exposure time affect seed viability and germination, seeds of five halophytes, Atriplex prostrata, Hordeum jubatum, Salicornia europaea, Spergularia marina, and Suaeda calceoliformis were exposed to 3.0, 5.0, and 10.0% NaCl solutions for 30, 60, 90, 365, and 730 d. Recovery experiments in distilled water indicated significantly different species responses to salinity over time. Percentage germination and rate of germination in H. jubatum were dramatically reduced following extended exposure and all seeds exposed to 10% NaCl for > 1 yr failed to germinate. Spergularia marina seeds were stimulated following short-term exposure to 3% NaCl; however, germination was delayed and overall germination was significantly reduced with exposure time in the two higher salinity levels. Percentage germination in A. prostrata decreased over time, but salinity level was not related to this reduction. Germination of S. europaea and S. calceoliformis, the most salt-tolerant species being tested, was stimulated by exposure to high salinity. Both species had a significant increase in percentage germination and in the germination rate when compared to seeds germinated in distilled water. Baseline germination data from seeds placed in 0, 1, 2, and 3% NaCl solutions indicated that S. europaea and S. calceoliformis were the only species to germinate in the 3% NaCl solution. Spergularia marina failed to germinate in the 2% NaCl treatment, and germination of A. prostrata and H. jubatum was significantly reduced at this salinity level. It is concluded that prolonged exposure to saline solutions can inhibit or stimulate germination in certain species, and the resulting germination and recovery responses are related to the duration and intensity of their exposure to salt in their natural habitats.     

Assessing the role of endophytic bacteria in the halophyte Arthrocnemum macrostachyum salt tolerance

• There is an increasing interest to use halophytes for revegetation of salt affected ecosystems, as well as in understanding their mechanisms of salt tolerance. We hypothesized that bacteria from the phyllosphere of these plants might play a key role in its high tolerance to excessive salinity.
• Eight endophytic bacteria belonging to Bacillus and closely related genera were isolated from phyllosphere of the halophyte Arthrocnemum macrostachyum growing in salty agricultural soils. The presence of plant‐growth promoting (PGP) properties, enzymatic activities and tolerance towards NaCl was determined. Effects of inoculation on seeds germination and adult plant growth under experimental NaCl treatments (0, 510 and 1030 mM NaCl) were studied.
• Inoculation with a consortium including the best performing bacteria improved considerably the kinetics of germination and the final germination percentage of A. macrostachyum seeds. At high NaCl concentrations (1030 mM), inoculation of plants mitigated the effects of high salinity on plant growth and physiological performance and, in addition, this consortium appears to have increased the potential of A. macrostachyum to accumulate Na⁺ in its shoots, thus improving sodium phytoextraction capacity.
• Bacteria isolated from A. macrostachyum phyllosphere seem to play an important role in plant salt tolerance under stressing salt concentrations. The combined use of A. macrostachyum and its microbiome can be an adequate tool to enhance plant adaptation and sodium phytoextraction during restoration of salt degraded soils.

     

THE EFFECT OF SALINITY AND TEMPERATURE ON THE GERMINATION OF POLYMORPHIC SEEDS AND GROWTH OF ATRIPLEX TRIANGULARIS WILLD.

Polymorphic seeds of Atriplex triangularis were germinated at various temperatures (5–15 C, 5–25 C, 10–20 C, 20–30 C) and salinity regimes (0 to 1.5% NaCl) in order to determine their germinability and early seedling growth under these conditions. Larger seeds generally had a higher germination percentage in saline medium. The rate and percentage of germination decreased with increased salinity stress. A thermoperiod of 25 C day and 5 C night, 12 hr/12 hr, temperature enhanced germination of seeds. Early seedling growth is promoted in larger seeds at lower salinity, and at high-day and low-night temperatures. Polymorphic seeds have different physiological requirements which provide alternative situations for seed germination in natural habitats.     

Alleviation of Salinity-Induced Dormancy in Perennial Grasses

All seeds of Aeluropus lagopoides and Urochondra setulosa germinated under non-saline conditions except for Sporobolus ioclados which showed only 40 % germination. Increase in salinity substantially inhibited germination and few seeds germinated at 400 mM NaCl. Germination at 200 mM NaCl was alleviated in U. setulosa by the application of gibberellic acid and fusicoccin, in A. lagopoides by thiourea, betaine, kinetin, fusicoccin and ethephon, and in S. ioclados by gibberellin and ethephon. High salinity (400 mM NaCl) induced germination inhibition was alleviated by proline, kinetin, fusicoccin and ethephon only in A. lagopoides.     

Germination responses of <Emphasis Type="Italic">Cymbopogon schoenanthus</Emphasis> to salinity

Germination studies of Cymbopogon schoenanthus (Poaceae) distributed along southern Tunisia were carried out to assess the effects of salinity. A preliminary experiment showed 30°C as the optimum germination temperature for seeds of this species. After that, seed germination was studied at different salinity levels. Our results revealed a decrease in germination percentage with increasing salinity. Germination rate, however, was maintained up to 200 mM NaCl and drastically declined at 300 mM NaCl.     

Effect of Salinity on Seed Germination,Growth, and Ion Accumulation of Atriplex patula (Chenopodiaceae)

Seeds and seedlings of the halophyte Atriplex patula were exposed to 0–2% NaCl to determine the effect of salt stress on germination and growth. Seeds germinated and plants survived and grew in solutions of up to 2.0% NaCl. Both seed germination and dry mass production were negatively affected by increased salinity. Dry mass production declined to 1% of controls and seed germination to 17% of controls in the 2% NaCl treatments, indicating that seeds were less inhibited than growing plants. Also, recovery treatments indicated that high salinity did not permanently injure seeds. Percent ash, and Na⁺ and Cl⁻ ions increased in shoots with each salt increment, while the K⁺ ion content decreased sharply. Atriplex patula is a facultative halophyte, and is limited to low and moderately saline sites because both seed germination and growth are severely reduced at salinities > 1% NaCl.     

盐度及种间相互作用对海三棱藨草、互花米草萌发及生长的影响

盐度和种间作用是影响湿地植物群落构建的关键因子。然而,已有研究主要集中于植物成体阶段,我们对生活史早期更新阶段的种间相互作用了解十分有限。崇明东滩国家级自然保护区是位于长江口的重要湿地,外来入侵植物互花米草对优势土著物种海三棱藨草的竞争排斥对当地生态系统造成了严重的负面影响。通过受控实验探讨了盐度及种间作用对海三棱藨草和互花米草种子萌发及生长的影响,以深入了解更新过程在盐沼湿地植物群落构建中的作用。结果表明,在培养皿中盐度对海三棱藨草的萌发有显著抑制作用,互花米草的萌发率受盐度影响不显著但萌发进程被延迟。混种处理对两者的萌发存在一定促进效应,且其作用强度受到盐度的调控。海三棱藨草与互花米草种子在萌发阶段的相互促进并非是通过化感作用实现的,可能是由于萌发过程对盐分的吸收减弱了盐胁迫的影响。盆栽条件下,两物种混种时的萌发及生长表现（高度、地上生物量）较单种时有所下降,但差异不显著。种间竞争受环境胁迫程度及生活史阶段的影响,竞争作用在胁迫较弱的淡水环境及生活史后期更强。盐沼湿地植物群落在形成早期受到盐度等环境因子的影响较大,不同植物对盐胁迫的响应是影响种群建成的主导因素,后期种间竞争的重要性不断增加,最终决定了植物群落的整体格局。     

Effects of salt,alkali and salt–alkali mixed stresses on seed germination of the halophyte Salsola ferganica (Chenopodiaceae)

Salsola ferganica L. (Chenopodianceae) is an annual halophytic species. Experiments were carried out in laboratory to determine the effects of temperature, perianths and various types of salinity on seed germination and germination recovery. Seeds were germinated at 6 levels of temperature with perianths, plus perianths and removed perianths in complete darkness for 9 days. The germination responses of the seeds without perianths at 25 °C were determined over a wide range of NaCl, NaHCO₃ or NaCl–NaHCO₃ mixed stress for 13 days. Perianths seriously affected germination as a barrier for seed germination and the optimal temperature was at 25 °C. Highest germination percentage was obtained under control and seed germination was progressively inhibited with the increase of salinity concentration. The negative effect of NaHCO₃ at the same concentration on germination was stronger than that of NaCl and NaCl–NaHCO₃ mixed. When substrate salinity was removed, seeds exposed to a high NaCl concentration (400–800 mM), NaHCO₃ (50–200 mM) and NaCl–NaHCO₃ mixed (100–400 mM) germinated well. Final germination of Salsola ferganica seeds was significantly affected by types of salt at the low salinity (?200 mM) and with increased salinity it was influenced mainly by salinity concentration for various proportion of salt–alkali mixed stress.     

Bracteoles affect germination and seedling establishment in a Mediterranean population of Atriplex portulacoides

The germination and subsequent seedling establishment of Atriplex portulacoides from a population in SW Spain were investigated in response to the presence or absence of attached bracteoles, at a range of NaCl concentrations (0–6%). Increasing salinity reduced both the final germination percentage and the speed of germination. The presence of bracteoles greatly inhibited germination and this effect was more marked with increasing salinity; bracteoles completely inhibited germination at salinities higher than 2%. The effects of salinity were substantially reversible, as cumulative germination after transfer of ungerminated seeds to distilled water was similar in all salinity treatments. This enforced dormancy could serve to prevent germination of floating fruits during dispersal in seawater. However, after transfer to distilled water the germination of seeds with bracteoles was still significantly lower than those without them, as a result of both higher dormancy and lower viability (as revealed by tetrazolium testing). Bracteoles thus also appear to enforce some physical dormancy. Seedlings derived from seeds with bracteoles demonstrated higher survival rates in fresh water than those derived from seeds without bracteoles but at 2% salinity there was no difference, and at higher salinities no seedlings of either type survived.     

The role of salinity in seed maturation of the euhalophyte Suaeda salsa

Controlled conditions were used to investigate how salinity maintains the salt tolerance of seeds and seedlings of the euhalophyte Suaeda salsa. Seeds were harvested from S. salsa plants that had been treated with 1 or 500 mM NaCl for 113 days in a glasshouse. The results showed that high salinity (500 mM NaCl) increased chlorophyll concentration and oxygen production in embryos of maturing seeds. At 500 mM NaCl, the phosphatidylglycerol and sulfoquinovosyldiacylglycerol levels and the digalactosyldiacylglycerol/monogalactosyldiacylglycerol ratio were higher in young seedlings derived from seeds whose source plants were cultured in 500 mM rather than in 1 mM NaCl. When seeds were incubated with 600 mM NaCl, the conductivity and malondialdehyde concentration in the embryos was greater if the source plants had been cultured in 1 mM rather than in 500 mM NaCl. The opposite pattern was evident for seedling survival and shoot weight. In conclusion, salinity during seed maturation may increase the salt tolerance of seeds and seedlings by increasing the oxygen production in the embryos of the maturing seeds and by changing the lipid composition of membranes in the seedlings.     

Effects of saline‐waterlogging and dryness/moist alternations on seed germination of halophyte and xerophyte

In arid zones, precipitation distribution is extremely uneven, with saline‐waterlogging and dry–moist cycles appearing frequently, which negatively impact on seed germination and seedling establishment. The responses of two halophytes, Suaeda physophora and Haloxylon ammodendron, and a xerophyte, Haloxylon persicum, to saline‐waterlogging and dry–moist cycles were studied. The results showed that aeration increased seed germination for all species when seeds were submerged in NaCl, especially for xerophyte. Compared with S. physophora and H. ammodendron, seed germination, recovery germination, and total germination of H. persicum were much lower when seeds were submerged in 700 mm NaCl, especially for the recovery germination and total germination of nongerminated seeds when the seeds were desiccated and then transferred to distilled water. However, when the seeds were submerged in 700 mm NaCl with aeration, the seed germination, recovery germination, and total germination of nongerminated seeds transferred to distilled water increased dramatically for H. persicum. No adverse effect of desiccation was found on those values of nongerminated seeds pretreated in NaCl with or without aeration for the two halophytes. In conclusion, seeds of the two halophytes were more tolerant to waterlogging and dry–moist cycles than seeds of the xerophyte during emergence under saline conditions; these traits may be important for halophytes to survive extreme saline environments during the seed germination stage.     

Full spectrum X‐ray mapping reveals differential localization of salt in germinating seeds of differing salt tolerance

Seeds of many coastal plants can survive exposure to seawater and may be dispersed long distances by the ocean. The salt tolerance or avoidance strategies of seeds are poorly understood, even though these traits may fundamentally influence dispersal and recruitment in coastal dunes. This research aimed to demonstrate how salt exclusion or localization within germinating seeds may affect salt tolerance. To determine the response of seeds to external salinity during imbibition (water uptake), it was necessary to quantify uptake and spatially resolve the internal distribution of salt. Flame photometry was used to quantify salt concentration in imbibing seeds and a new application of full‐spectrum X‐ray mapping allowed visualization of the spatial distribution and relative abundance of salt. As external salinity increased, salt‐sensitive Spyridium globulosum (Rhamnaceae) seeds accumulated sodium and chlorine in the seed embryo, while potassium was increasingly displaced and germination was reduced. Conversely, salt‐tolerant Ficinia nodosa (Cyperaceae) seeds avoided ion uptake and germination was not affected by imbibition in high sodium chloride (NaCl) concentrations. These results provide insight into mechanisms of salt tolerance/avoidance during imbibition and early germination and suggest that oceanic dispersal can be a viable explanation for the distribution of some plant species. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 129–142.     

SEED GERMINATION RESPONSE AND EVIDENCE FOR HEIGHT ECOPHENES IN SPARTINA ALTERNIFLORA FROM NORTH CAROLINA

A study was conducted to determine germination response to temperature and salinity and seedling response to salinity by three height forms of the salt marsh grass Spartina alterniflora Loisel. Germination tests showed that seeds cannot withstand drying at moderate temperature, as viability was lost within 40 days in seeds stored dry at 72 F. Cold storage at 43 F is adequate to prevent desiccation up to 40 days, but after 8 months viability is lost. Viability is retained at least 8 months when seeds are stored in sea water at 43 F. Germination response was good in a 65–95 F alternating diurnal thermoperiod but was poor in a 72 F constant thermoperiod. Germination response to salinity was an inverse curvilinear relationship with germination inhibition at high salinities apparently due to osmotic effects. The maximum tolerance limit for germination lies between 6 and 8 % NaCl. Seeds from short, medium, and tall plants responded similarly in storage and temperature studies. However, in salinity studies, seeds of the Ocracoke Island short form and the Oak Island tall form performed best. A logarithmic curve best described seedling growth response to various NaCl levels. Growth response as measured by seedling dry weight was best in 0.5 % NaCl solution. Seedlings grew taller in both 0.5 and 1.0 % NaCl than in 0 % NaCl. No significant difference in seedling growth response due to height form of the parent plant was detected. Thus, on the basis of germination and seedling responses, the height forms of S. alterniflora in North Carolina salt marshes are best described as ecophenes.     

High salinity impacts germination of the halophyte Cakile maritima but primes seeds for rapid germination upon stress release

Seed germination recovery aptitude is an adaptive trait of overriding significance for the successful establishment and dispersal of extremophile plants in their native ecosystems. Cakile maritima is an annual halophyte frequent on Mediterranean coasts, which produces transiently dormant seeds under high salinity, that germinate fast when soil salinity is lowered by rainfall. Here, we report ecophysiological and proteomic data about (1) the effect of high salt (200 mM NaCl) on the early developmental stages (germination and seedling) and (2) the seed germination recovery capacity of this species. Upon salt exposure, seed germination was severely inhibited and delayed and seedling length was restricted. Interestingly, non‐germinated seeds remained viable, showing high germination percentage and faster germination than the control seeds after their transfer onto distilled water. The plant phenotypic plasticity during germination was better highlighted by the proteomic data. Salt exposure triggered (1) a marked slower degradation of seed storage reserves and (2) a significant lower abundance of proteins involved in several biological processes (primary metabolism, energy, stress‐response, folding and stability). Yet, these proteins showed strong increased abundance early after stress release, thereby sustaining the faster seed storage proteins mobilization under recovery conditions compared to the control. Overall, as part of the plant survival strategy, C. maritima seems to avoid germination and establishment under high salinity. However, this harsh condition may have a priming‐like effect, boosting seed germination and vigor under post‐stress conditions, sustained by active metabolic machinery.     

沙枣和柠条种子萌发期耐盐性研究

采用室内控制实验的方法,系统研究了沙枣和柠条种子萌发、生长、活力以及生理过程;对萌发、生长及活力指标与盐胁迫进行相关与回归分析,发现了实验室条件下沙枣和柠条种子萌发期的耐盐临界值;对生理指标与盐胁迫,生理指标与相应的萌发及生长指标进行相关性分析,在生理水平对沙枣和柠条种子萌发期对盐胁迫的响应进行了解释。主要结果包括：(1)胚根相对干重含水量与盐胁迫无相关性,初始萌发时间、休眠率以及死亡率与盐胁迫呈显著正相关,其它指标均与盐胁迫呈显著负相关;(2)胚根相对干重含水量与萌发种子初期生长无相关性,休眠率、死亡率与萌发率呈显著负相关,其它指标均与初期生长呈显著正相关;(3)受盐胁迫的抑制程度：萌发速度>萌发启动>萌发率;胚根生长>胚轴生长>萌发率;(4)种子萌发期,沙枣耐盐性强于柠条,两者耐盐临界值均高于0.1 mol·L^-1。     

Seed germination of Pilosocereus arrabidae (Cactaceae) from a semiarid region of south‐east Brazil

We evaluated the effect of temperature regimes (six constant and four alternating temperatures), light qualities (five red : far red ratios) and water potentials (ΨW; seven NaCl and polyethylene glycol 6000 [PEG] solutions) on the percentage and germination rate, as well as the post‐seminal development morphology, that allow Pilosocereus arrabidae seeds to germinate in a hot semiarid climate on the south‐eastern Brazilian coast. The results showed that seeds germinated similarly between constant and alternating temperatures, with an optimal germination at 25/20°C and 20°C. Pilosocereus arrabidae seeds were photoblastic positive and the final germination percentage was inhibited at low red : far red ratios. Maximum germination was obtained in distilled water (0 MPa) and decreases of Ψ_W in the solutions reduced the germination, which was lower in NaCl than in iso‐osmotic PEG solutions. Germination inhibition appears to be osmotic because the recovery response was high when non‐germinated seeds from both iso‐osmotic solutions were transferred to water. Seeds of P. arrabidae are small and germination is phaneroepigeal. Despite the slow growth typically seen in seedlings and adults of Cactaceae, germination in this species depends on the ability of the seeds to appropriately sense and react to environmental cues that correlate with times and places under low‐risk growth conditions.     

Effect of oxygen availability and salinity on EARLY LIFE HISTORY STAGES OF SALT MARSH PLANTS. I. Different germination strategies of Spartina alterniflora and Phragmites australis (Poaceae)

Gradients in oxygen availability and salinity are among the most important environmental parameters influencing zonation in salt marsh communities. The combined effects of oxygen and salinity on the germination of two salt marsh grasses, Spartina alterniflora and Phragmites australis, were studied in growth chamber experiments. Germination of both species was initiated by emergence of the shoot and completed by root emergence. Percentage S. alterniflora germination was reduced at high salinity (40 g NaCl/L) and in decreased oxygen (5 and 2.5%). In 0% oxygen shoots emerged, but roots did not. P. australis germination was reduced at a lower salinity (25 g NaCl/L) than S. alterniflora, and inhibited at 40 g NaCl/L and in anoxia. However, a combination of hypoxia (10 and 5% O2) and moderate salinity (5 and 10 g NaCl/L) increased P. australis germination. When bare areas in the salt marsh are colonized, the different germination responses of these two species to combinations of oxygen and salt concentrations are important in establishing their initial zonation. In high salinity wetlands S. alterniflora populates the lower marsh and P. australis occupies the high marsh at the upland boundary.     

Germination responses of Diplotaxis harra to temperature and salinity

Diplotaxis harra (Forssk.) Boiss, an annual herb in the family of Brassicaceae, is widely distributed in many sandy and gypseous areas in southern Tunisia. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and recovery responses after seed transfer to distilled water. The germination responses of the seeds in complete darkness were determined over a wide range of temperatures (5, 10, 15, 20, 25 and 30 °C) and salinities (0, 50, 100, 150 and 200 mM NaCl). Germination was inhibited by either an increase or decrease in temperature from the optimal temperature (15 °C). Highest germination percentages were obtained under non-saline conditions and an increase in NaCl concentrations progressively inhibited seed germination. Rate of germination decreased with an increase in salinity at all temperatures but comparatively higher rates were obtained at 15 °C. Salt stress decreased both the percentage and the rate of germination. An interaction between salinity and temperature yielded no germination at 200 mM NaCl. Seeds were transferred from salt solution to distilled water after 20 days, and those from low salinities recovered at all temperatures. At NaCl concentration of 200 mM, the recovery of germination was completely inhibited.     

Effects of maternal salinity on salt tolerance during germination of Suaeda aegyptiaca,a facultative halophyte in the Arab Gulf desert

Suaeda aegyptiaca is a facultative halophyte found in saline and non‐saline habitats of the Arab Gulf desert, which produces small‐sized undispersible seeds. The interactive effects of maternal salinity and other environmental conditions, such as salinity, light and temperatures, that are prevailing during seed germination have received little attention for a facultative halophyte. This study tested the effects of maternal salinity on salt tolerance during seed germination of S. aegyptiaca under different light and temperature regimes. Seeds collected from both saline and non‐saline habitats of the United Arab Emirates (UAE) were germinated in 0, 50, 100, 200 and 400 mM NaCl, and incubated at 15/25°C, 20/30°C and 25/35°C in both 12‐h light/12‐h dark regimes and continuous darkness. Generally, seeds of the non‐saline habitat were 56% heavier and attained greater germination at the lower temperatures than seeds of the saline habitat. Seeds of the saline habitat germinated better in saline solutions at higher temperatures and in light. Germination was faster for seeds of the saline habitat than for seeds of non‐saline habitats. Germination recovery after transfer to distilled water was significantly greater for seeds from the non‐saline habitat, compared with seeds from saline habitats. Recovery was greater at lower and/or moderate temperatures, compared with at higher temperatures. Germination was significantly faster during recovery, compared with in the saline solutions. The study indicates that the maternal effect of salinity was confounded with the seed‐size effect and it cannot be conclusively confirmed.     

Seed Germination in Relation to Salinity and Temperature in Sarcobatus Vermiculatus

Sarcobatus vermiculatus (Hook) Torrey is a leaf succulent, sodium-accumulating shrub usually found in saline substrates of the Great Basin desert, Utah, USA. Laboratory experiments were conducted to determine the effect of salinity (0, 200, 400, 600, 800 and 1000 mM NaCl) and temperature (day/night: 5/15, 10/20, 15/25, 20/30, and 25/35°C) on seed germination. S. vermiculatus showed 100% germination in non-saline controls, at all thermoperiods. Percentage and rate of germination decreased with increases in salinity and few seeds germinated at even 1000 mM NaCl. High salinity exposure caused the loss of viability at higher temperature regimes, while some recovery was recorded in low salinity treatments.