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.     

Does salt stress increase the ability of the exotic legume Acacia longifolia to compete with native legumes in sand dune ecosystems?

Sand dune ecosystems are one of the areas most affected by the introduction of invasive species which represents a threat for biodiversity conservation. Their invasion patterns and spread may depend on their salinity tolerance, besides other factors. To test this hypothesis, we investigated the effects of salt stress on seed germination and on the activity of antioxidant enzymes (catalase, CAT; ascorbate peroxidase, APX; peroxidase, POX; and glutathione reductase, GR) in two legume species, an invasive, Acacia longifolia (Andrews.) Willd., and a native, Ulex europaeus (L.), very common in the sand dunes of the coast of Portugal. Salt stress was induced by adding NaCl at different concentrations, 0, 50, 100 and 200 mM, for 15 days. Results showed that the highest germination percentages were obtained in distilled water (control) and that, with increasing salt concentration, seed germination was delayed and decreased in both species. Inhibition of germination was higher in the native species, only 3% of seeds germinated at 100 mM and no seeds germinated at 200 mM NaCl. In the invasive species, the reduction was higher at 200 mM NaCl (16%). Considering the coefficient of germination velocity, a decrease in both species with increasing NaCl concentration was observed. The CAT and GR activities decreased in A. longifolia with increasing salinity. In turn, APX activity significantly increased as NaCl concentration increased while the POX activities declined at the highest NaCl concentration. On the other hand, at 50 mM NaCl lower activity of CAT and APX and higher GR and POX were found in U. europaeus. In both species, protein content increased as NaCl concentration increased. In addition, it seems that APX activities play an essential role in the scavenging reactive oxygen species (ROS). These results suggest that the seeds of the invasive legume A. longifolia are more tolerant to salinity than the native legume U. europaeus, and seem better equipped to handle the physiological stress of high salinity, which may contribute to its invasive ability in sand dunes.     

Differential salt-stress response during germination and vegetative growth in in vitro selected somaclonal mutants of Cenchrus ciliaris L.

Four somaclonal mutants (S1, S4, S6 and M10) and their parental Cenchrus ciliaris L. cultivar Biloela were characterized under salinity conditions at germination and vegetative growth stages. Seeds of all somaclonal mutants had higher germination percentages than cv. Biloela seeds in the control and salt treatments. At 150 mM, germination was significantly higher in M10, S6 and S4 (72.3%, 66.3% and 61.8%, respectively) than in cv. Biloela (35.5%). Mutants grown under salinity along with cv. Biloela for 35 days had a different relative growth rate. S6 had the highest growth rate, indicating its potential tolerance to salt stress, whereas M10 was the most sensitive, with Bi, S4 and S1 being intermediate tolerant genotypes. Catalase enzyme activity (CAT) in M10 decreased in response to salt stress and was significantly associated with malondialdehide content, suggesting salt injury, whereas higher levels of CAT activity in S6 during salt stress were associated with increased salinity tolerance. The present results indicate that somaclonal variation and in vitro mutagenesis offer an effective tool for improvement of C. ciliaris because the somaclonal mutants showed differential tolerance to salt stress with respect to their parental and could be a better choice for use in a breeding program.     

Role of calcium in alleviating effect of salinity on germination of Phragmites karka seeds

Phragmites karka (Retz.) Trin, ex. steud, a perennial reed with creeping rhizome from the family Poaceae, is distributed as pure population in brackish water swamps. Populations primarily propagate using ramets but also produce numerous seeds which form part of the seed bank after dispersal and are exposed to extremes of temperature, drought, and salinity stress. Seeds were germinated under a range of salinity (0, 100, 200, 300, 400, 500 mM NaCl) and temperature (10/20 °C, 15/25 °C, 20/30 °C, 25/35 °C, night/day) regimes in 12 h light:12 h dark photoperiod or in complete darkness with 0, 5, 10, 25 mM CaCl₂. Salinity, absence of light and high temperature (25/35 °C) reduced germination while calcium generally reversed this effect, more so at cooler temperature regimes. Calcareous soil around Karachi would help alleviate the salinity effect on the germination of P. karka and facilitate its survival.     

Silicon supply in soilless cultivations of zucchini alleviates stress induced by salinity and powdery mildew infections

In the present study, the hypothesis was tested as to whether silicon supplied via the nutrient solution is capable of enhancing the tolerance of hydroponically grown zucchini squash (Cucurbita pepo L. cv. ‘Rival’) to salinity and powdery mildew infections. Two experiments were conducted involving a low (2.2 dS m^?1, 0.8 mM NaCl) and a high salinity level (6.2 dS m^?1, 35 mM NaCl) in combination with a low (0.1 mM) and a high (1.0 mM) Si level in the nutrient solution supplied to the crop. The exposure of the plants to high external salinity restricted significantly the vegetative growth as well as the fruit yield of zucchini due to a reduction of both the number of fruits per plant and the mean fruit weight. However, the inclusion of 1 mM of Si in the salinized nutrient solution mitigated the salinity-associated suppression of both growth and yield. Part of the growth and fruit yield suppression at high salinity was due to restriction of net photosynthesis. The stomatal conductance was also restricted by salinity, whereas the substomatal CO₂ concentration was not affected by the NaCl or Si treatments. The supply of 1 mM of Si via the nutrient solution mitigated the inhibitory effect of salinity on net photosynthesis and this effect was associated with lower Na and Cl translocation to the epigeous plant tissues. Furthermore, the supply of Si via the nutrient solution suppressed appreciably the expansion of a powdery mildew (Podosphaera xanthii) infection in the leaves at both salinity levels. These results indicate that the supply of at least 1 mM of Si via the nutrient solution is capable of enhancing both tolerance to salinity and resistance to powdery mildew in soilless cultivations of zucchini squash.     

Exogenous nitric oxide improves seed germination in wheat against mitochondrial oxidative damage induced by high salinity

Effects of exogenous nitric oxide (NO) on starch degradation, oxidation in mitochondria and K⁺/Na⁺ accumulation during seed germination of wheat were investigated under a high salinity level. Seeds of winter wheat (Triticum aestivum L., cv. Huaimai 17) were pre-soaked with 0 mM or 0.1 mM of sodium nitroprusside (SNP, as nitric oxide donor) for 20 h just before germination under 300 mM NaCl. At 300 mM NaCl, exogenous NO increased germination rate and weights of coleoptile and radicle, but decreased seed weight. Exogenous NO also enhanced seed respiration rate and ATP synthesis. In addition, seed starch content decreased while soluble sugar content increased by exogenous NO pre-treatment, which was in accordance with the improved amylase activities in the germinating seeds. Exogenous NO increased the activities of superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6); whereas decreased the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), and superoxide anions (O₂^??) release rate in the mitochondria. Exogenous NO also decreased Na⁺ concentration while increased K⁺ concentration in the seeds thereby maintained a balance between K⁺ and Na⁺ during germination under salt stress. It is concluded that exogenous NO treatment on wheat seeds may be a good option to improve seed germination and crop establishment under saline conditions.     

Is broad-scale smoke–water application always a useful tool for improving seedling emergence in post-mining restoration? Evidence from jarrah forest restoration in Western Australia

It has been widely advocated that smoke–water application to topsoil can substantially improve restoration success by enhancing seed germination. This is despite few studies having tested the effects of smoke–water on seedling emergence in field-scale restoration trials. Here we report the effects of applying a commercially available smoke solution (Regen 2000®), at rates between 0 and 100 mL m^− 2, on jarrah forest sites being restored after bauxite mining in the southwest of Western Australia. Smoke solutions stimulated the seed germination of a range of species in laboratory experiments. In addition, smoke–water stimulated germination of Stylidium affine seeds sown directly into the first field experiment. However, apart from the effect on sown S. affine seeds, smoke–water application had no effect on subsequent seedling numbers, species richness or the relative proportion of seedlings in different growth-form categories in either of the two field experiments. These findings suggest that smoke–water application does not always ensure enhanced restoration outcomes.     

Effect of yak rumen content treatments on seed germination of 11 alpine meadow species on the Qinghai-Tibetan Plateau

The Qinghai-Tibetan Plateau is located in the ‘Third Pole’ of the world, characterized by a harsh environment. Despite this, the alpine meadow ecosystem have developed over a wide area but serious grassland degradation is threatening the ecological environment on the Plateau. Recruitment of new plants to the population, via germination and establishment, is vital to plant community survival. Previous work on the seeds in this area has mainly focused on community-wide germination strategies, seed germination characteristics and their correlations with seed size and seed mass. However, there have been no studies on the effects of soaking in rumen contents on the plant seed germination characteristics of alpine meadow species. The present study had two main objectives: (i) to determine the effect of fresh rumen content from yaks on seed germination characteristics and seedling growth of species common to the eastern Tibetan Plateau alpine meadow, and (ii) to develop an effective method to enhance seed germination. Seeds of 11 common species were collected together with fresh rumen content from three yaks that grazed there. Seed germination tests were conducted after they had been soaked in rumen content for one of six soaking periods (12, 24, 36, 48, 60 or 72 h). The seeds were incubated under natural light conditions of 8 h light at 25 °C and 16 h darkness at 15 °C, for the germination period of 34 days. The results showed that seed germination and seedling growth were affected by soaking time, seed coat completeness and seed type. After soaking in rumen content, the germination percentages of scarified (peeled or with the seed coat cut through) seeds of some species (true seeds Oxytropis ochrocephala and Medicago ruthenia var inschanica, nutlet Carex enervis, achenes Anemone rivularis and Polygonum sibiricum) and complete seeds of C. enervis, and A. rivularis were improved but the duration of soaking was also important. Seed germination of caryopsis Achnatherum inebrians (a toxic grass) was significantly inhibited by any exposure to rumen fluids. Scarified seeds generally had higher germination percentages than complete ones after treatment, but with the increase in soaking time, germination percentages declined and scarified seeds were more sensitive to the treatment than the complete seeds. After soaking in yak rumen content, the germination indices of scarified M. ruthenia at 12 h treatment, O. ochrocephala and achene Rumex acetosa at 12–24 h treatment, nutlet Kobresia humilis at 24 h treatment, P. sibiricum at 24–48 h treatment, C. enervis at 12–48 h treatment and A. rivularis at 12–60 h treatment were significantly higher than the control (P < 0.05), while the germination indices of complete C. enervis seeds at 12 h and 36 h treatment, and A. rivularis at 12–60 h treatment were significantly higher compared with the control. The germination indices of other species gradually decreased with the increase in soaking time. We concluded that yak rumen digestion could enhance, inhibit or not affect seed germination and seedling growth of the alpine meadow species, which might influence seedling recruitment, interspecific competition, and the plant community structure of the eastern Tibetan Plateau alpine meadow. Overall, yak digestion has a positive effect on alpine meadow seed germination and seed dispersal.     

Comparison of salinity tolerance of three Atriplex spp. in well-watered and drying soils

Members of the Chenopodiaceae are well adapted to both salt and drought stress and can serve as model species to understand the mechanisms of tolerance in plants. We grew Atriplex hortensis (ATHO), A. canescens (ATCA), and A. lentiformis (ATLE) along a NaCL salinity gradient under non-water-limited conditions and in drying soils in greenhouse experiments. The species differed in photosynthetic carbon fixation pathway, capacity for sodium uptake, and habitat preferences. Under non-water-limited conditions, ATLE (C4) maintained high growth rates up to 30 g L⁻¹ NaCl. ATHO (C3) had lower growth than ATLE at high salinities, while ATCA (C4) grew more slowly than either ATLE or ATHO and showed no net growth above 20 g L⁻¹ NaCl. ATHO and ATLE accumulated twice as much sodium in their shoots as ATCA, but all three species had increasing sodium levels at higher salinities. Potassium, magnesium and calcium levels were relatively constant over the salinity gradient. All three species showed marked accumulation of chloride across the salinity gradient, whereas nitrate, phosphorous and sulfate decreased with salinity. The effect of drought was simulated by growing plants in sealed pots with an initial charge of water plus NaCl, and allowing them to grow to the end point at which they no longer were able to extract water from the soil solution. Drought and salinity were not additive stress factors for Atriplex spp. in this experiment. NaCl increased their ability to extract water from the soil solution compared to fresh water controls. ATLE showed increased shoot dry matter production and increased water use efficiency (WUE) as initial salinity levels increased from 0 to 30 g L⁻¹ NaCl, whereas dry matter production and WUE peaked at 5 g L⁻¹ for ATHO and ATCA. Final soil moisture salinities tolerated by species were 85 g L⁻¹, 55 g L⁻¹ and 160 g L⁻¹ NaCl for ATHO, ATCA and ATLE, respectively. C4 photosynthesis and sodium accumulation in shoots were associated with high drought and salt tolerance.     

Germination response and viability of an endangered tropical conifer Widdringtonia whytei seeds to temperature and light

The tropical conifer Widdringtonia whytei Rendle is an endangered species endemic to Mulanje Mountain in Malawi. A study was conducted for the first time under controlled conditions in order to assess the effects of temperature and light on germination and viability of W. whytei seeds. Seeds incubated at a constant temperature of 20 °C attained the highest cumulative germination percentage (100%) followed by 87% germination under fluctuating temperatures of 15 °C night/25 °C day. No seed germination occurred at temperatures below 15 °C. Seeds that failed to germinate at temperatures below 15 °C showed the highest (> 90%) viability compared to the seeds incubated at 25 °C (60%). Across temperature regimes, germination was significantly higher under light (44.7%) than dark (35.6%) conditions. It is concluded that temperature is one of the critical factors for germination of W. whytei seed. The ability of W. whytei seeds to germinate both in light and darkness implies that the species would unlikely form a persistent soil seed bank, an attribute which is common in species that survive in habitats frequently disturbed by fires.     

Effects of various salts on the germination of three perennial salt marsh species

We studied the germination responses of Arthrocnemum macrostachyum, Juncus acutus and Schoenus nigricans to saline stress caused by different salt types. The germination percentage and mean time to germination data were obtained by incubating seeds for 30 d in 1, 2, 3, 4 or 5% saline solutions of NaCl, MgCl₂, MgSO₄ and Na₂SO₄ at 30/20 °C and with a 12 h photoperiod. A. macrostachyum was the most tolerant species to salinity during the germination (65% in 2% NaCl). S. nigricans showed the lowest germination (none germinated in salt and only 26% in distilled water). J. acutus showed intermediate behaviour between the two above species, its germination being inhibited by high salt concentrations. The sulphates had less inhibitory effect than the equivalent chloride concentrations.     

In vitro salinity tolerance of two pistachio rootstocks: Pistacia vera L. and P. atlantica Desf

Seedlings of Pistacia vera L. and Pistacia atlantica Desf. were cultured on hormone-free DKW medium supplemented with NaCl. The plants were subjected to low NaCl concentrations ranging from 0 to 80 mM for 45 days or to high salt concentrations (0, 131, and 158.5 mM for P. vera and 0, 131, and 240 mM for P. atlantica) for 25 days. Toxicity symptoms were recorded for seedlings exposed to low NaCl treatments. Plant growth, survival rates, mineral content, as well as proline and soluble sugar contents were determined and evaluated at the end of the culture period. The results indicated that low NaCl treatments yielded no instances of plant death in both species. At high salt conditions, however, significant mortality rates were noted for both species, being 22.86% at 240 mM NaCl for P. atlantica and 25.8% at 158.5 mM NaCl for P. vera. With regards to salinity effects, levels of 60 and 80 mM NaCl induced significant decreases of stem elongation and leaf number in the P. vera species. Salinities between 40 and 80 mM NaCl, however, induced a decrease in the root number of both species. The fresh weights of P. vera and P. atlantica also decreased significantly after 45 days of culture at NaCl concentrations between 40 and 80 mM and after 25 days of culture at 158.5 and 240 mM NaCl, respectively. The sodium and chloride uptake in plant organs seemed to be controlled more efficiently in P. atlantica than in P. vera. In both species, the K⁺ content was noted to undergo a significant decrease when salinity increased. While the K⁺/Na⁺ ratio was maintained above 2 at low NaCl treatments, it was sharply decreased at high NaCl conditions, suggesting a failure of K–Na selectivity mechanism. The Ca²⁺/Na⁺ ratio decreased significantly at 60 and 80 mM NaCl in P. vera and at 60 mM NaCl for P. atlantica. In both Pistacia species, high NaCl treatments (131–240 mM NaCl) induced a significant increase in proline content.     

Seed storage and germination in Kumara plicatilis,a tree aloe endemic to mountain fynbos in the Boland,south-western Cape,South Africa

Seed storage under appropriate conditions is a relatively inexpensive means of safeguarding plant genetic material for ex situ conservation. Post-storage germination trials are used to determine the viability of stored seeds, and hence the efficacy of the particular storage treatment. Kumara plicatilis (= Aloe plicatilis) is a tree aloe endemic to mountain fynbos in the Boland, south-western Cape. The viability and germination behaviour of K. plicatilis seeds were assessed for seeds stored for four and nine months at − 80 °C, 4 °C, 25 °C and under ambient conditions in a laboratory. Seeds were germinated under controlled conditions and germination rates and percentages determined. Ungerminated seeds were tested for viability using tetrazolium salt. Seed viability was not significantly reduced during storage. Seeds stored at − 80 °C for four and nine months exhibited the fastest germination rate overall (both 5.9 ± 0.3 weeks, mean ± S.E.), and slowest was for seeds stored under ambient conditions for four and nine months (both 7.8 ± 0.4 weeks). All seed lots showed similar percentage germination after four months of storage (78.0–90.4%). The highest percentage germination overall was for seeds stored at − 80 °C for four months (90.4%) and the lowest was for seeds kept at 4 °C and − 80 °C for nine months (39.2 and 39.6%, respectively). Respective percentage viability for ungerminated seeds in these two treatments was 82% and 87%, respectively, indicating the induction of secondary dormancy. Induced dormancy triggered by protracted cold temperatures may be an adaptation that enables seeds to survive prolonged extreme conditions that are unfavourable for germination. Further research on the long-term storage of aloe seeds would be beneficial for developing long-term seed storage and germination testing protocols for ex situ conservation.     

Differential tolerance to combined salinity and O2 deficiency in the halophytic grasses Puccinellia ciliata and Thinopyrum ponticum: The importance of K+ retention in roots

Saline environments of terrestrial halophytes are often prone to waterlogging, yet the effects on halophytes of combined salinity and waterlogging have rarely been studied. Either salinity or hypoxia (low O₂) alone can interfere with K⁺ homeostasis, therefore the combination of salinity or hypoxia is expected to impact significantly on K⁺ retention in roots. We studied mechanisms of tolerance to the interaction of salinity with hypoxia in Puccinellia ciliata and Thinopyrum ponticum, halophytic grasses that differ in waterlogging tolerance. Plants were exposed to aerated and stagnant saline (250 mM NaCl) treatments with low (0.25 mM) and high (4 mM) K⁺ levels; growth, net ion fluxes and tissue ion concentrations were determined. P. ciliata was more tolerant than T. ponticum to stagnant-saline treatment, producing twice the biomass of adventitious roots, which accumulated high levels of Na⁺, and had lower shoot Na⁺. After 24 h of saline hypoxic treatment, MIFE measurements revealed a net uptake of K⁺ (∼40 nmol m⁻² s⁻¹) for P. ciliata, but a net loss of K⁺ (∼20 nmol m⁻² s⁻¹) for the more waterlogging sensitive T. ponticum. NaCl alone induced K⁺ efflux from roots of both species, with channel blocker tests implicating GORK-like channels. P. ciliata had constitutively a more negative root cell membrane potential than T. ponticum (−150 versus −115 mV). Tolerance to salinity and hypoxia in P. ciliata is related to increased production of adventitious roots, regulation of shoot K⁺/Na⁺, and a superior ability to maintain negative membrane potential in root cells, resulting in greater retention of K⁺.     

Effects of seed storage on germination of two succulent desert halophytes with little dormancy and transient seed bank

Seeds of both Salsola imbricata and Haloxylon salicornicum have high germination level and germination speed, and form a transient seed bank in nature. The impacts of storage period and condition on germination level and speed were assessed in the two species. Storage for three months significantly increased both germination level and speed of seeds stored under the different conditions, compared to that of fresh seeds. In both species, nine months storage did not affect germination percentage in cold storage seeds, but completely inhibited it in field seeds. Storage for longer time in room and warm temperatures resulted in significant reduction or complete inhibition in the germination of the two species, so this was more pronounced in H. salicornicum. Storage significantly increased germinate rate index of seeds stored in all conditions till 17 months in S. imbricata and till 12 months in H. salicornicum. In both species, fridge storage had little effects on final germination and germination speed of seeds incubated at the different temperatures, compared to fresh seeds. However, room temperature and warm storages significantly reduced final germination and germination speed at the different temperatures, so the reduction was more pronounced at 35 °C, especially in H. salicornicum.     

Germination responses of Croton macrostachyus (Euphorbiaceae) to various physico-chemical pretreatment conditions

Croton macrostachyus Hochst. ex Del. (Euphorbiaceae) is a multipurpose, deciduous, and medium sized tree of pantropic occurrence. Because the species has numerous useful qualities (e.g., establishment and growth in disturbed sites, drought tolerance, fast growth rate, copious litter/necromass production, suitability for agroforestry, and ability to attract avian frugivores), its speedy restoration has become increasingly critical. Germination studies were therefore conducted on seeds pooled from five widely located provenances with a view to supporting efforts geared toward the speedy propagation and restoration of this valuable tree species. Seed pretreatments were achieved using various dilution levels of plant-derived smoke–water (1:1, 1:10, 1:100 and 1:1000), as well as gibberellic acid (GA₃) or potassium nitrate (KNO₃) ranging in concentration from 0.1 to 100 μmol. The control was to use distilled water for seed pretreatment. Seeds were germinated under either illuminated (ca 60 μmol m^− 2 s^− 1; cool-white fluorescent lamp) or non-illuminated conditions. Experiments on the impact of seed storage durations, as well as storage temperatures were also conducted. The study found that germination percentage (GP: ca 90%), and mean germination time (MGT: 14 days) were significantly (P < 0.001) better when seeds were pretreated with smoke–water and germinated under non-illuminated conditions, than when these were pretreated with various concentrations of GA₃ or KNO₃ (GP and MGT of ca 65% and 20 days, respectively). Germination percentage (GP) and germination vigor (GV) declined with increasing storage-time for all storage temperatures, but GV's decline was faster for seeds stored at 22 °C than for those stored at 5 and 15 °C. On the other hand, mean germination time (MGT) increased significantly (P < 0.01) with seed storage-time of up to 8 months at 5, 15, and 22 °C, but the increase was more marked for seeds stored at 22 °C than for those stored at 5 and 15 °C. From these investigations, it is concluded that germination of C. macrostachyus seeds through use of smoke–water is faster, cheaper, and technically less demanding, compared to that of either GA₃ or KNO₃. The study also concludes that C. macrostachyus is intermediate between orthodox and recalcitrant seeds, and that it is non-photoblastic.     

The maternal environment determines the timing of germination in Pinus pinaster

Optimizing the germination timing is crucial for the establishment of new generations. We hypothesized that environmental maternal effects may be relevant in the fine tuning of this trait in a long-lived Mediterranean model tree. We analyzed the influence of maternal genotype, maternal environment and their interaction on the germination success and germination phenology of 8725 Pinus pinaster seeds collected from genotypes clonally replicated in two contrasting environments. Besides maternal genetic effects, the maternal environment significantly affected both the percentage and the timing of germination. Seeds from the more favourable environment germinated 7.5 days earlier and showed higher germination rate (0.93 ± 0.01 vs 0.85 ± 0.03). Seed weight significantly influenced germination time, but seed weight differences between maternal environments were not enough to explain this form of transgenerational plasticity. The effect of the maternal environment varied depending on the genotype, indicating that genetic variation in the sensitivity to the maternal environment in this pine species does exist.     

Eco-physiological responses to salinity changes across the freshwater-marine continuum on two euryhaline bivalves: Corbicula fluminea and Scrobicularia plana

The influence of global climate change will potentially alter the salinity of aquatic ecosystems. This represents a tremendous challenge for societies worldwide. Different sources of salinization (natural or anthropogenic) amplify the introduction of salt in rivers and streams, causing an increase of salt flowing down to estuarine and coastal areas. In this study, Corbicula fluminea and Scrobicularia plana have been selected because of their large tolerance for salinity variation (euryhaline organisms). They will allow the study of effect on the whole spectrum of salinity from fresh to marine waters respectively. The aim was to study the impact of experimental salinity stress at physiological, biochemical and behavioral levels by exposing both species to a salinity close to their limit range of tolerance, 15 practical salinity unit (psu), and at their field salinity (1.5 psu and 30 psu for C. fluminea and S. plana respectively) in the presence or absence of food during 2 and 7 days of exposure. Negative impacts of hyper saline condition for C. fluminea (15 psu) and hypo saline condition for S. plana (15 psu) have been measured at biochemical, physiological and behavioral levels. At sub-individual and individual levels, structural and energetic parameters and behavioral impairments seemed to be suitable biomarkers to assess salinity stress on C. fluminea and S.plana. After exposure to the limit of salinity tolerance (15psu) for both organisms, fitness modifications could appear, and may participate in endangering populations.     

Tropical seagrass species tolerance to hypersalinity stress

The long-term sustainability of seagrasses in the subtropics and tropics depends on their ability to adapt to shifts in salinity regimes, particularly in light of present increases in coastal freshwater extractions and future climate change scenarios. Although there are major concerns world-wide on increased salinity in coastal estuaries, there is little quantitative information on the specific upper salinity tolerance of tropical and subtropical seagrass species. We examined seagrass hypersalinity tolerance under two scenarios: (1) when salinity is raised rapidly simulating a pulsed event, such as exposure to brine effluent, and (2) when salinity is raised slowly, characteristic of field conditions in shallow evaporative basins; the first in hydroponics (Experiments I and II) and the second in large mesocosms using intact sediment cores from the field (Experiment III). The three tropical seagrass species investigated in this study were highly tolerant of hypersaline conditions with a slow rate of salinity increase (1 psu d⁻¹). None of the three species elicited total shoot mortality across the range of salinities examined (35–70 psu over 30 days exposures); representing in situ exposure ranges in Florida Bay, a shallow semi-enclosed subtropical lagoon with restricted circulation. Based on stress indicators, shoot decline, growth rates, and PAM florescence, all three species were able to tolerate salinities up to 55 psu, with Thalassia testudinum (60 psu) and Halodule wrightii (65 psu) eliciting a slightly higher salinity threshold than Ruppia maritima (55 psu). However, when salinity was pulsed, without a slow osmotic adjustment period, threshold levels dropped 20 psu to approximately 45 psu for T. testudinum. While we found these three seagrass species to be highly tolerant of high salinity, and conclude that hypersalinity probably does not solely cause seagrass dieoff events in Florida Bay, high salinity can modify carbon and O₂ balance in the plant, potentially affecting the long-term health of the seagrass community.     

Determination of seed viability of eight wild Saudi Arabian species by germination and X-ray tests

Our purpose was to evaluate the usefulness of the germination vs. the X-ray test in determining the initial viability of seeds of eight wild species (Salvia spinosa, Salvia aegyptiaca, Ochradenus baccatus, Ochradenus arabicus, Suaeda aegyptiaca, Suaeda vermiculata, Prosopisfarcta and Panicumturgidum) from Saudi Arabia. Several days were required to determine viability of all eight species via germination tests, while immediate results on filled/viable seeds were obtained with the X-ray test. Seeds of all the species, except Sa.aegyptiaca, showed high viability in both the germination (98–70% at 25/15 °C, 93–66% at 35/25 °C) and X-ray (100–75%) test. Furthermore, there was general agreement between the germination (10% at 25/15 °C and 8% at 35/25 °C) and X-ray (5%) tests that seed viability of Sa.aegyptiaca was very low, and X-ray analysis revealed that this was due to poor embryo development. Seeds of P.farcta have physical dormancy, which was broken by scarification in concentrated sulfuric acid (10 min), and they exhibited high viability in both the germination (98% at 25/15 °C and 93% at 35/25 °C) and X-ray (98%) test. Most of the nongerminated seeds of the eight species except those of Sa.aegyptiaca were alive as judged by the tetrazolium test (TZ). Thus, for the eight species examined, the X-ray test was a good and rapid predictor of seed viability.