Seed germination in Marathrum schiedeanum and M. rubrum (Podostemaceae)

Marathrum schiedeanum and Marathrum rubrum are annual Podostemaceae, thus their seeds are important to their dispersal and persistence in their habitat. We assessed the effect on germination of (1) light (white, red and far red) and darkness, (2) temperature (15, 20, 25, 30 °C and alternating 20/30 °C), (3) osmotic potential (0 to −0.8 MPa), (4) proximity to moisture sources and (5) seed storage. Seeds of M. schiedeanum and M. rubrum were non-dormant and had a high germination capacity (96%). Seeds were positive photoblastic; at 15 °C germination drop to zero, and germination rate was slower at 20 °C and at 20/30 °C than at 25 °C. A small proportion of seeds of both species germinated even at osmotic potentials as low as −0.6 MPa (11%) for M. rubrum and −0.8 MPa (70%) for M. schiedeanum. Seeds germinated only when near to the source of moisture (91.3–87.1% and 53.3–35.6% for M. schiedeanum and M. rubrum, respectively) and 2 years in dry storage did not modify their capacity to germinate. At the beginning of the rainy season, light and temperature in the rivers may be high enough for germination. The ability to germinate at low osmotic potential may be related to early germination during the rainy season. This may be because the seed mucilage assists in diffusion of water from the substrate to the seed. Both species germinated faster at −0.06 MPa, than in distilled water, which may indicate appropriate conditions for germination of these short-lived species.     

The effect of temperature, water level and burial depth on seed germination of Myriophyllum spicatum and Potamogeton malaianus

The effects of temperature, water level and burial depth on seed germination of two submerged species, Myriophyllum spicatum and Potamogeton malaianus, were investigated under controlled laboratory conditions. There was no significant difference in final germination of M. spicatum among water level treatments, but P. malaianus germinations at 1 cm and 12 cm water levels were better than at 0 cm water level at temperatures of 20 °C and 30 °C. Little to no germination was observed for either species at the temperature of 10 °C. At 15 °C, however, germination increased significantly to 66.3-70.6% for M. spicatum and to 29.4-48.1% for P. malaianus under all three water level treatments. Increased temperature from 15 °C to 30 °C had no significant effect on the final germination of M. spicatum except at the 1 cm water level, but enhanced significantly the germination of P. malaianus. Analysis of the mean time to germination revealed that M. spicatum was a faster germinator relative to P. malaianus. The two species’ germination differed markedly in response to burial depth. Germination percentage of M. spicatum was 71.3% at 0 cm burial depth, but decreased to 5.0% and to 2.5% at depths of 1 cm and 2 cm, respectively; whereas germination percentages of P. malaianus were 40.0%, 23.8%, 12.5%, 7.5% and 1.3% at depths of 0 cm, 1 cm, 2 cm, 3 cm and 5 cm, respectively. We concluded that the two species respond differently to germination strategies. The findings provided further insight into how germination strategy contributes to the seed bank formation and species invasion.     

Laboratory germination of seeds from 10 British species of Potamogeton

Factorial laboratory germination experiments were carried out on fruits from 10 British species of Potamogeton (Potamogetonaceae). Fruits had all been placed in a dry-room maintained at 15% RH and 15 °C for 3–6 months from the time of collection.     

Cold stratification,light and high seed density enhance the germination of Ottelia alismoides

The effects of cold stratification, light and seed clustering in petri dish on Ottelia alismoides seed germination were investigated. The seeds required light and an extended cold period in order to germinate, but neither treatment alone was effective. Seed germination significantly increased with length of the 4 °C cold stratification period. Freshly collected seeds failed to germinate while a 5-month period at 4 °C yielded 29 ± 9% germination in the light, but none in the dark. Treatment with sodium nitroprusside, a nitric oxide source, failed to promote germination in the light or dark. Seeds of O. alismoides showed an unusual and significant positive response to aggregation. Germination in the light, after 5-month 4 °C cold stratification, was stimulated to almost five-fold in the dishes that were more densely sown with seed (20 seeds versus 200 seeds). Likewise, clustering seeds in dense aggregations stimulated germination significantly. Germination more than quadrupled with an increase from 1 to 50 seeds per cluster (200 seeds per dish), reaching a value of 72 ± 4%. Linear regression analysis shows the correlation between seed cluster density (no. per cluster) and germination rate (%) was highly significant (R² = 0.85, P = 0.000). The extended cold stratification requirement is probably an over-wintering device. The mechanism of the density-dependent stimulation is unclear.     

Seed germination at different temperatures and water stress levels,and seedling emergence from different depths of Ziziphus lotus

Ziziphus lotus (L.) Lam. is a deciduous shrub with intricately branched stems in the Rhamnaceae family. It's a dominant and economically important species widely distributed in active sand dunes in the southern desert of Tunisia. To provide basic information for its conservation and reintroduction, we studied the influence of environmental factors on seed germination patterns. The germination responses of seeds were determined over a wide range of constant temperatures (10–50 °C), polyethylene glycol (PEG)-6000 solutions of different osmotic potentials (0 to − 1 MPa) and burial depths (1–10 cm). Temperatures between 15 and 45 °C seem to be favorable for the germination of this species. Germination was inhibited by either an increase or decrease in temperature from the most suitable temperature found (35 °C). The highest germination percentages (100%) were obtained under control conditions without PEG, and increasing moisture stress progressively inhibited seed germination, which was less than 5% at − 1 MPa. When tested for germination in distilled water, after PEG treatments, seeds germinated to the same extent as when fresh. When seeds buried deeply, there was a significant decrease in seedling emergence percentage and rate. Seedlings of Z. lotus emerged well at depths of 1–2 cm and could not emerge when sand burial depth was > 4 cm.     

Effects of pre-treatments and temperature on seed viability and germination of Juniperus macrocarpa Sm.

The effects of collecting season, collection site, laboratory pre-treatments and temperatures on seed viability and germination of Juniperus macrocarpa were investigated. Ripe cones were collected in four Sardinian dune systems, in two seasons, from plant and soil. Warm (W) and cold (C) stratifications, two combinations of them (W + C, C + W), and no pre-treatment (0) were applied. Seeds were incubated in a range of constant (10–25 °C) and an alternating (25/10 °C) temperature regime. Seed viability was low (ca. 40%) and varied significantly according to the collecting season. Seed germination was also low (ca. 10%), the 0 and W were the most effective pre-treatments on stimulating germination. The best germination temperature, without any pre-treatment, was 15 °C (ca. 20%). J. macrocarpa seeds are dormant and the achieved results suggested that the presence of secondary dormancy is induced by cold stratification. Spring appeared to be the best season for seed collecting, whereas autumn was the best for sowing. These results give new findings for restoration activities on this species.     

Seed flotation and germination of salt marsh plants: The effects of stratification, salinity, and/or inundation regime

We examined the effects of cold stratification and salinity on seed flotation of eight salt marsh species. Four of the eight species were tested for germination success under different stratification, salinity, and flooding conditions. Species were separated into two groups, four species received wet stratification and four dry stratification and fresh seeds of all species were tested for flotation and germination. Fresh seeds of seven out of eight species had flotation times independent of salinity, six of which had average flotation times of at least 50 d. Seeds of Spartina alterniflora and Spartina patens had the shortest flotation times, averaging 24 and 26 d, respectively. Following wet stratification, the flotation time of S. alterniflora seeds in higher salinity water (15 and 36 ppt) was reduced by over 75% and germination declined by more than 90%. Wet stratification reduced the flotation time of Distichlis spicata seeds in fresh water but increased seed germination from 2 to 16% in a fluctuating inundation regime. Fresh seeds of Iva frutescens and S. alternflora were capable of germination and therefore are non-dormant during dispersal. Fresh seeds of I. frutescens had similar germination to dry stratified seeds ranging 25-30%. Salinity reduced seed germination for all species except for S. alterniflora. A fluctuating inundation regime was important for seed germination of the low marsh species and for germination following cold stratification. The conditions that resulted in seeds sinking faster were similar to the conditions that resulted in higher germination for two of four species.     

Dormancy and germination in Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee seeds: Effects of short-time moist chilling and plant growth regulators

We investigated the germination requirements of the species Stachys germanica L. subsp. bithynica (Boiss.) Bhattacharjee (Lamiaceae). We studied the effects of scarification, short-time moist chilling (+4 °C) for 15 and 30 days, and various doses of gibberellic acid (GA₃; 0, 100, 150 and 250 ppm), Kinetin (KIN; 50 ppm) and a combination of 250 ppm GA₃ and 50 ppm KIN. The hormone and moist chilling treatments were carried out under both continuous darkness (20 °C) and photoperiodic (20/10 °C; 12/12 h, respectively) conditions. Seeds failed to germinate in response to short-time moist chilling treatments with distilled water under both continuous darkness and photoperiodic conditions. Seeds were found to have dormancy. Treatments with GA₃ or a combination of GA₃ and KIN were successful at breaking seed dormancy. A maximum of 37% of the seeds germinated after GA₃ application in all series. When only KIN was applied at a 50 ppm concentration, germination (12%) was found only with moist chilling for 30 days under continuous darkness. The highest germination rates were found in seeds treated with combination of 250 ppm GA₃ and 50 ppm KIN. In the combination treatments, while the moist chilling treatments for 15 days resulted in 68 and 73% germination, respectively, these rates were up to 95% in the moist chilling treatments for 30 days under continuous darkness and photoperiodic conditions. Mean germination time (MGT) in GA₃ and KIN combinations was lower than in other treatments. Scarification with 80% sulphuric acid did not promote germination. The characteristics of physiological dormancy of S. germanica ssp. bithynica seeds are consistent with conditions of existence in the in alpine habitat of this species.     

Germination performance of congeneric Styrax species from the Cerrado sensu lato areas and their distribution pattern in different physiognomies

When studying congeneric species, it is of reasonable importance to understand different ecophysiological performances which might determine the distribution of species in habitats with different natural resources. Styrax ferrugineus is exclusive and well adapted to the Brazilian Cerrado sensu stricto (s. str.); S. camporum is widely distributed in the Cerrado sensu lato (s. l.) areas, with young trees being observed at the edge of cerradão and other vegetation fragments; and S. pohlii occurs in permanently waterlogged soils of the Cerrado region, such as those of riparian forests. We tested the hypothesis that the higher the soil water content in the physiognomic gradient of the vegetation, the higher is the germination success of S. pohlii, but the lower is the germination success of S. ferrugineus. We also discuss whether gap conditions inside a cerradão fragment imply a high germination rates of seeds of S. camporum. Seeds from each of the three species were buried within nylon bags containing soil from the respective sites. Burial occurred in a Cerrado s. str., in understory and gap conditions of a cerradão, and in the understory of a riparian forest fragment, and lasted for 60, 120, 180 and 240 days, respectively, after the fruit dispersal time of each of the three species. After 60 days, a relationship was found showing that the percentage of germinated seeds diminished, and the percentage of damaged seeds increased as soil water content increased (Cerrado s. str. < cerradão gap < cerradão understory ? riparian forest). S. camporum still showed viable seeds 60 days after burial (DAB), and germinated seeds 120 DAB, indicating that it needed a longer time to germinate, which might be associated to its thicker seed coat, in relation to the other two species. The germination performance of each of the three species was the same in the gap and understory conditions of the cerradão. The higher concentration of adult S. camporum plants at the edge of vegetation fragments is not related to a particular high germination performance and seedling establishment.     

Seed germination of Lasia spinosa as a function of temperature,light, desiccation,and storage

Lasia spinosa seeds were not dormant at maturity in early spring. The most favorable temperatures for germination were between 25 and 30 °C, and final percentage and rate of germination decreased with an increase or decrease in temperature. When L. spinosa seeds were transferred to 25 °C, after 60 days at 10 °C (where none of the seeds germinated), final germination increased from 0% to 78%. Seeds germinated to high percentage both in light and in dark, although dark germination took more than twice as long as in the light. During desiccation of seeds at 15 °C and 45% relatively humidity, moisture loss decreased exponentially from 2.02 to 0.13 g H₂O g⁻¹ dry wt within 16 days, and only a few seeds (12%) survived 0.13 g H₂O g⁻¹ dry wt moisture content. Seeds stored at 0.58 g H₂O g⁻¹ dry wt moisture content at four constant temperatures (4, 10, 15, and −18 °C) for up to 6 months exhibited a well-defined trend of decreasing viability with decreasing temperature. Thus, we concluded that freshly harvested L. spinosa seeds are non-dormant and recalcitrant. Also, the seeds with 0.58 g H₂O g⁻¹ dry wt moisture content could be effectively stored for a few months between 10 and 15 °C although the most appropriate temperature for wet storage appears to be 10 °C, as it is close to the minimum temperature for germination and so there will be less pre-sprouting compared to 15 °C.     

Tolerance and recovery responses of playa halophytes to light,salinity and temperature stresses during seed germination

Halogeton glomeratus (M. Bieb.) C.A. Mey., Lepidium latifolium Linn. and Peganum harmala Linn. are distributed in temperate salt playa habitats of Upper Hunza, Pakistan. Seeds were germinated under various salinity (0–500 mM NaCl), light (12 h-light:12 h-dark and 24 h-dark) and temperature (5/15, 10/20, 15/25, 20/30, and 25/35 °C, dark/light) regimes for 20 days to determine the optimal conditions for germination and recovery of seeds from these factors when exposed to less than optimal conditions. Seeds that failed to germinate in dark were transferred successively to 12 h-photoperiod, salinity to distilled water and from various temperature regimes to 20/30 °C, to determine the effect of these stresses and the ability of these seeds to recover respectively. Highest seed germination (H. glomeratus and L. latifolium: 100%; P. harmala: 80%) was obtained in non-saline control at 20/30 °C in 12 h-photoperiod, however, increase in salinity progressively inhibited seed germination. Seed germination of H. glomeratus and P. harmala was substantially inhibited and that of L. latifolium was prevented in dark. Salinity and dark treatments have a synergistic effect in inhibiting seed germination of all species. No seed of any species germinated at 5/15 °C; germination was substantially inhibited at 25/35 °C both for H. glomeratus and P. harmala while L. latifolium failed to germinate at 25/35 °C. Rate of germination also decreased with an increase in salinity at all temperature regimes but this effect was minimal at optimal temperature regime of 20/30 °C. After successive elimination of light, salinity and temperature stresses, final seed germination was identical to respective controls. The results indicate that seeds of these temperate halophytes could endure environmental stresses without losing viability and germinate readily when these stresses are removed. Under the extremely variable conditions of the playa habitat these species are highly opportunistic exploiting the windows of opportunity available during spring or early summer.     

Morphological characteristics of annual Zostera marina shoots at various germination temperatures

The timing of the transition from seed, seedlings and development into flowering is paramount importance in annual-type Zostera marina, because flowering is the first step of sexual reproduction. A majority of plants use environmental cues to regulate the transition to their developmental stages because plants must flower synchronously for successful outcrossing and must complete their sexual reproduction under favorable external conditions. The morphological characteristics (seeds and lateral shoot production, branch number, and inflorescence length) of reproductive shoots of Z. marina L. were examined in outdoor mesocosms to better understand the reproductive strategies of annual populations. Seeds in the germination experiment were divided into two groups: those exposed to cold (7 °C; vernalized group) and those left untreated (25-21 °C; non-vernalized group). All 600 seeds (300 from each group) were cultured for 2 months at 7, 10, 15, 20, and 25 °C in an indoor incubator. In the vernalized group, the germination rates were almost significantly higher than in the non-vernalized group. However, germination rates were not significantly affected by germination temperature. In outdoor mesocosms, production of vegetative shoots was observed in plants germinated at 15 and 20 °C in the vernalized group and at 10, 15 and 20 °C in the non-vernalized group. The highest number of vegetative shoots produced (35) was observed in plants germinated at 20 °C in the vernalized group, whereas seeds of either group failed to produce vegetative shoots when germinated at a low temperature (7 °C).In the flowering phase, the number of branches per shoot in the vernalized group was significantly higher than in the non-vernalized group. The total number of spadices on the 1st branches of plants in the vernalized group (germination at 20 °C) was significantly lower than that in the non-vernalized group at the same germination temperature. The total number of spadices per reproductive shoot in the vernalized group (germination at 10 °C) was also higher than in the non-vernalized group. Thus, both low temperature (vernalization) and seed germination temperature have implications for the sexual and asexual propagation of annual Z. marina populations.     

Influence of environmental factors on Vallisneria americana seed germination

Over the course of a growing season (April–October) water quality (water temperature, light, salinity, dissolved oxygen) and reproductive phenology (biomass, production of flowering shoots and seed pods, seed bank densities) were quantified in three Vallisneria americana beds in Nanjemoy Creek, MD, a tributary to the Chesapeake Bay. Clonal production of V. americana biomass increased at all sites when water temperatures rose above 25 °C. Flowering occurred during peak biomass (August–September) and resulted in the production of up to 16,000 seeds m⁻² at the end of the growing season. However, observed seed bank densities represented <1% of seed production. Laboratory experiments quantified the effects of dissolved oxygen (0.29–8.00 mg l⁻¹), light (0–160 μmol m² s⁻¹), temperature (13–29 °C), salinity (0.1–17.4 psu), sediment composition (3–86% sand; 0.9–8.3% sediment organic content), and burial depth (0.2–10 cm) on V. americana seed germination. Germination of V. americana seeds was enhanced (greater overall germination and shorter time to germination) under oxygenated conditions (8.00 mg l⁻¹), temperatures >22 °C, salinities of <1 psu, and in sediments composed of ≤3% organic content and >40% sand. Light (<160 μmol m⁻² s⁻¹) and burial depth (0.2–10 cm) had no significant effects on germination. Temperatures most favorable for seed germination (>22 °C) occurred in June, 2 months in the growing season just prior to development of peak vegetative standing stock. Seedlings were therefore at a distinct disadvantage to plants developed from over wintering buds. A lack of viable seed retention and inadequate environmental conditions at critical times in the growing season may be limiting seed germination success and subsequent seedling establishment within V. americana beds in the Chesapeake Bay. However, ungerminated seeds were found to maintain high viability, especially at salinities of 10 psu that can have significant negative effects of shoot growth survival. This suggests that seeds may serve as a source of reproductive material for bed recovery after periods of drought or other stressful conditions in estuarine systems.     

Effect of temperature on sporulation of Neozygites floridana isolates from different climates and their virulence against the tomato red spider mite, Tetranychus evansi

The fungal pathogen Neozygites floridana Weiser and Muma has been evaluated as a classical biological candidate for introduction into Africa against the invasive tomato red spider mite Tetranychus evansi Baker and Pritchard. In this study, the effect of temperature on sporulation, germination and virulence of three isolates of N. floridana collected from T. evansi in three climatically distinct regions of Brazil and Argentina was determined. Six constant temperatures of 13 °C, 17 °C, 21 °C, 25 °C, 29 °C and 33 °C were tested for their effect on the ability of the three fungal isolates to sporulate, germinate and kill the mites. Six alternating-temperature regimes of 17-13 °C, 21-13 °C, 29-13 °C, 33-13 °C, 33-23 °C, 33-28 °C under a 12 h photophase were also tested to estimate virulence of the three isolates against T. evansi. The Vipos isolate discharged more conidia than isolates from Recife or Piracicaba at all temperatures and sporulation was strongly temperature dependent. Optimal sporulation rates were observed at 25 °C while optimal germination rates were observed at 25 °C and 29 °C. At 29 °C, the shortest mean survival time of T. evansi (3.16 days, 95% CI of 3.05-3.27) was observed for the isolate from Vipos, while the longest LT₅₀ (3.47 days, 95% CI 3.34-3.59) was observed for the isolate from Piracicaba. Mortality of mites increased as the differences between alternating day and night temperatures increased from 8 °C (21-13 °C), to 10 °C (33-23 °C), to 16 °C (29-13 °C), with smallest and highest temperature differences of 4 °C (17-13 °C) and 20 °C (33-13 °C), both producing low mortalities. The overall results suggest that the Vipos isolate is better adapted to a wider range of temperatures than the other isolates tested.     

Suitable water temperature for seed storage of Zostera japonica for subtropical seagrass bed restoration

Restoration of Zostera japonica is needed. Laboratory culture experiments to know the germination characteristics might be helpful for implementation of actual restoration. As a part of germination experiments, we explored suitable water temperature for long-term storage of Z. japonica seeds. This work was based on earlier reports of Zostera marina, which presumably has similar physiological properties to Z. japonica. This study consisted of two experiments: (1) preservation experiments to investigate the fate of stored Z. japonica seeds and (2) germination experiments to investigate the germination potential of the stored seeds. The results of the preservation experiments suggested that seed condition, that is, germinated, degraded, unstable, stable, etc., showed variations between the seeds stored at 4 and 23 °C. The majority of the seeds stored at 4 °C were germinated, while those at 23 °C seemed to be degraded, presumably by bacteria and mold. The germination experiments suggested high germination potential of seeds stored at 4 °C even after 302 days had elapsed. In conclusion, including previously reported results on Z. marina, low temperature was suitable for the preservation of seeds to maintain germination potential.     

Intraspecific variation of seed floating ability in Sparganium emersum suggests a bimodal dispersal strategy

Water-mediated spread of seeds (hydrochory) plays an important role in the dispersal of aquatic plants. In this study we investigate intraspecific variation in floating ability and germination capacity of Sparganium emersum seeds in relation to seed mass, within three natural populations along the Rur River (the Netherlands–Germany). Our results suggest that S. emersum produces two types of seeds: (i) short-floating seeds (SFS) that sink within 4 weeks (approximately 71% of all seeds), and (ii) long-floating seeds (LFS) that float at least for 6 months (approximately 28% of all seeds). Our study further shows that short-floating seeds display a significantly higher germination (%) (SFS = 89.9% vs LFS = 32.6%), a faster germination rate (SFS = 8.71 ± 3.3 vs LFS = 9.32 ± 3.1 days to germination) and a higher mean seed mass (SFS = 15.17 ± 4.5 vs LFS = 11.25 ± 3.8 mg), compared to long-floating seeds. It is argued that the production of these two types of seeds by S. emersum plants, each type with a different potential for water-mediated dispersal, represents a bimodal hydrochoric dispersal strategy.     

An efficient method for organic acetylation and use of dl-phosphinothricin as a negative selection agent in argE transgenic rice

We present an efficient method for the production of N-acetyl-l-phosphinothricin (N-AcPt) from commercial dl-phosphinothricin (DL-PPT) by organic acetylation for use as a negative selection agent (NSA) that induces cell death in argE transgenic rice. DL-PPT was efficiently converted into N-AcPt with tetrahydrofuran (THF) and acetic anhydride (Ac₂O). Chemical changes were confirmed using NMR and ATR-FTIR analyses. DL-PPT was toxic but N-AcPt did not show cytotoxic effects on leaf discs or seed germination of wild-type rice. Conversely, in argE–hpt transgenic rice, non-toxic N-AcPt showed the negative selection (NS) effect by inducing cell destruction in leaf discs and restricting seed germination. For inducing NS, ?0.1 mg ml⁻¹ and ?0.5 mg ml⁻¹ of N-AcPt were effective in leaf and seed assays, respectively. Further, the NS effect occurred faster in the leaf assay compared with the seed germination assay, again indicating the leaf assay was a more sensitive indicator of N-AcPt as an NSA to argE transgenic rice than the seed germination assay. This negative selection approach could be useful for the development of selectable marker free transgenic plants in the economically important monocot species and its commercialization for multiple gene transformation.     

Germination and early growth of Nymphaea odorata at different water depths

We experimentally determined the effects of water depth on seed germination and seedling growth and morphology, and we documented the transition from submerged to emergent plants in the white water lily, Nymphaea odorata. Seeds of N. odorata were germinated at 30, 60, and 90 cm water depth in outdoor mesocosms and percent germination and morphology measured after a month. The presence of self-seeded seedlings in pots at the same 3 water levels was also recorded over two years. To examine juvenile growth, seeds planted in soil were placed at the same mesocosm depths; germination and growth were monitored for three months, when the plants were harvested for morphological and biomass measurements. N. odorata germinated equally well in 30, 60 and 90 cm water; seedlings grew as submerged aquatics. After one month, seedlings in 90 cm water had less biomass than those in 30 cm (1.1 vs. 3.3 mg and 1.0 vs. 1.8 mg for different seed sources, respectively) and allocated relatively more biomass to shoots (97.5 vs. 67.8% and 73.1 vs. 58.0%, respectively). Seedlings in 60 cm water were intermediate. After 3 months of submerged growth, plant biomass remained less in 90 vs. 60 and 30 cm water (22.5 vs. 36.4 and 33.3 mg, respectively). Plants in 90 and 60 cm water had greater biomass allocation to shoots than plants in 30 cm water (85.7 and 72.6% vs. 64.4%, respectively) and produced larger laminae on longer petioles (lamina length = 33.3 vs. 25.2 mm in 90 vs. 30 cm; petiole length = 99.0 vs. 36.0 mm, respectively). After about 3 months, submerged plants produced floating leaves that had 39% shorter laminae but 267% to 1988% longer petioles than submerged leaves on the same plant. Lamina length to width allometric relations of submerged leaves were >1 at all water levels, distinguishing them from the equal allometry of adult floating leaves. The switch from production of submerged to emergent leaves resembles submergence-escape growth in other aquatics, but because the seedlings have been submerged throughout their life, submergence itself cannot be the stimulus to produce emergent leaves in these totally immersed plants. Our data show that N. odorata plants can establish from seeds in up to 90 cm water and that seedlings grow as submerged aquatics until they switch abruptly to production of floating leaves.     

Effect of desiccation level and storage temperature on green spore viability of Osmunda japonica

In order to effectively preserve green spores, which have relatively higher water content and lose viability more quickly than non-green spores, we studied the effect of desiccation level and storage temperature on Osmunda japonica spores. The water content of fresh spores was 11.20%. After 12 h desiccation by silica gel, the water content decreased to 6% but spore viability did not change significantly. As the desiccation continued, the decrease in water content slowed, but spore viability dropped. For almost all storage periods, the effects of storage temperature, desiccation level, and temperature × desiccation level were significantly different. After seven days of storage, spores at any desiccation level stored at 4 °C obtained high germination rates. After more than seven days storage, liquid nitrogen (LN) storage obtained the best results. Storage at −18 °C led to the lowest germination rates. Spores stored at room temperature and −18 °C all died within three months. For storage at 4 °C and in LN, spores desiccated 12 and 36 h obtained better results. Spores without desiccation had the highest germination rates after being stored at room temperature, but suffered the greatest loss after storage at −18 °C. These results suggest that LN storage is the best method of long-term storage of O. japonica spores. The critical water content of O. japonica spores is about 6% and reduction of the water content to this level improves outcome after LN storage greatly. The reason for various responses of O. japonica spores to desiccation and storage temperatures are discussed.     

Influence of heat on seed germination of seven Mediterranean Leguminosae species

The influence of high temperatures (dry heat and hot water) on germination of seven Mediterranean Leguminosae species typical of fire-prone ecosystems in southern Spain is analyzed, in order to know the response of seeds to wildfires and the possible implications in their regeneration after this disturbance. Seeds were heated to a range of temperatures (50 °–150 °C) and exposure times (1–60 min) similar to those registered in the upper soil layers during wildfires. Germination tests were carried out in plastic Petri dishes over 60 days. In general, the degree of seed germination promotion by dry heat treatments showed a wide interspecific variation, although the final germination level was increased in all the studied species except for Scorpiurus muricatus. The thermal pretreatment of 50 °C, however, was not effective for germination in any species, and rising the temperature to 70 °C only slightly enhanced the germination in Cytisus patens. The preheatings of 90 °C (5 and 10 min), 120 °C (5 and 10 min), and 150 °C (1 min) were the most effective in promoting seed germination. Hot water (100 °C) scarification also increased the final germination level in all cases, with the exception of C. patens. The germination rates after preheating were much lower than in mechanically scarified seeds and closely resembled those of the untreated seeds, except for C. reverchonii, whose seed germination rate decreased with heat. The response of species to heat shock had no clear relationship with life trait or with the specific post-fire regeneration strategy (obligate seeder or facultative resprouter). Those species coexisting in the same habitats had different heat optimal requirements for seed germination, an strategy suggested by some authors as minimizing interspecific competition in the secondary succession started after fire.