Absolute Light Requirement For Germination Research Articles

Sunlight and red to far-red ratio impact germination of tropical montane cloud forest species

Context Australia’s tropical montane cloud forests (TMCF) exhibit exceptional species richness and endemism. Determinants of regeneration via seed of these species are next to unknown, limiting our ability to quantify and project their vulnerability to climate change. The ratio of red to far-red light (R:FR) has been shown to influence seed germination of many tropical species. Aims We investigated germination of six previously unstudied TMCF species in relation to the presence or absence of light (light/dark) and light quality (R:FR). We hypothesised that increased R:FR would lead to increased germination and that small-seeded species would be more likely to have a light requirement and be less sensitive to R:FR compared to larger-seeded species. Methods Sunlight and polyester filters were used to create a gradient of R:FR ranging from 0.1 to 1.14. Seeds were also sown in constant darkness. Key results Across species we saw varying germination responses. Three of the four smallest-seeded species exhibited an absolute light requirement for germination and did not discriminate between different R:FR. Germination of the small-seeded TMCF endemic Dracophyllum increased exponentially with increasing R:FR. Germination of the largest-seeded species was inhibited by both low and high R:FR, and germination was higher in constant darkness than diurnal light/dark. All six species were able to germinate at remarkably low R:FR values. Conclusions Light affects seed germination of Australia’s TMCF plant species in a variety of ways. Implications The findings of this study provide insights into plant recruitment in situ, and the acclimation potential of these species under reduced R:FR predicted for the future.

Thermal niche for seed germination of Xyris species from Brazilian montane vegetation: Implications for climate change

AbstractUnderstanding how climate change will affect regeneration from seeds is important for developing conservation strategies. We evaluated seed germination requirements for sympatric species of Xyris from montane rupestrian grasslands (campo rupestre) in Brazil to determine their thermal niche and thermal requirements for seed germination. We also assessed whether projected temperature increases would affect seed germination of the species. Seed germination was evaluated at a wide range of constant temperatures (10–40°C) under light (12‐hr photoperiod) and dark conditions. Base temperatures (Tb) and thermal times for 50% germination (θ50) were calculated for three species. The effects of projected mean temperature increase on seed germination percentage and timing were evaluated. All species revealed an absolute light requirement for germination. Thermal germination niche breadth was greatest for X. asperula (15 to 35°C) and narrowest for X. seubertii (20 and 25°C). Base temperatures for X. asperula, X. pilosa and X. trachyphylla were 9.0, 12.8 and 11.1°C, respectively. In the scenario with the highest temperature increase (A2), the greatest reductions in seed germination are observed for X. pilosa and X. seubertii. The lowest projected temperature increase (2°C) was sufficient to decrease by 1 day the germination time of X. asperula and X. pilosa. Species of Xyris do not present a pattern for thermal germination niche and thermal requirements values, indicating that the effects of climate warming on the regeneration of these seeds will probably vary among species.

Enhancing Conservation of a Globally Imperiled Rockland Herb (Linum arenicola) through Assessments of Seed Functional Traits and Multi-Dimensional Germination Niche Breadths.

Humans currently face an extraordinary period of plant biodiversity loss. One strategy to stem further losses involves the development of species-level recovery plans that guide conservation actions. Seeds represent an important component in the life history of plants and are crucial for conservation activities. Yet, most recovery plans contain meager seed biology information. We set out to examine seed functional traits and germination niche breadth of Linum arenicola seeds exposed to a range of thermal, photoperiodic, and salinity gradients to gain perspectives on the seed biology of this endangered species that may inform conservation decision making and assist recovery plan development. We found that fresh seeds possess non-deep physiological dormancy, which may be alleviated via a four-week dry after-ripening treatment. The germination response of non-dormant seeds is subsequently promoted by constant rather than alternating temperatures. The optimum germination temperature range is 20–22 °C. Non-dormant seeds do not possess an absolute light requirement for germination, but are sensitive to low levels of salinity (EC50 = 6.34 ppth NaCl). The narrow thermal and salinity germination niche breadths reported here suggest a specialized reproductive strategy that may require careful consideration when planning ex and in situ conservation activities.

Germination ecology of the perennial herb Xyris longiscapa: inter-annual variation in seed germination and seasonal dormancy cycles

AbstractGermination ecology was investigated in a natural population of Xyris longiscapa, a perennial herbaceous species endemic to the Brazilian campo rupestre. Seeds were collected over four consecutive years (2014 to 2017) to evaluate germination responses to a range of temperatures (from 15 to 30°C). The light requirement was evaluated in seeds collected in 2014. Seeds collected in 2014 were also buried in soil in the natural habitat of the species to evaluate changes in germinability at different temperatures over the time. Seeds showed an absolute light requirement for germination. Seed germination was affected by temperature, collection year and the interaction between these two factors. Seeds collected in 2014 showed a narrower temperature range for germination (15–20°C), compared with the seeds collected in 2015, 2016 and 2017 that germinated in a temperature range of 15–25°C. Buried seeds remained viable in soil for at least 14 months and exhibited seasonal dormancy cycling. Secondary dormancy was induced during the rainy season and alleviated during the dry season, following a conditional dormancy/dormancy cycle. The degree of primary dormancy appeared to be influenced by the environmental conditions experienced by seeds during maturation. Primary dormancy (when present), seed persistence in soil and seasonal dormancy cycles are strategies of X. longiscapa to enhance regeneration success in the harsh environment of the Brazilian campo rupestre.

Germination ecology of three endangered river corridor plants in relation to their preferred occurrence

As a contribution to conservation, we investigated germination requirements of three perennial, endangered river corridor plants of Central European lowlands coexisting in subcontinental flood meadows, but preferring particular zones of decreasing flooding frequency and duration along the elevational gradient of the banks. It was hypothesized that the species have specific germination requirements to respond successfully to open patch creation depending on their occurrence along the gradient of spring flooding in the field. This study involved controlled experiments and phenological studies. Juncus atratus and Gratiola officinalis, which frequently occupy flooded, naturally disturbed sites, have an absolute light requirement for germination, typical of pioneer species. Summer-dispersed, non-dormant seeds of J. atratus did hardly germinate at high temperatures and lacked a gap sensitivity based on temperature fluctuation. Since the temperature amplitude decreases beneath an insulating cover of vegetation or water, seeds seem to be prepared for rapid germination at open, wet, maybe even inundated sites. Late-summer-dispersed seeds of G. officinalis were in a state of conditional primary dormancy. Dormancy could be completely broken by cold–wet stratification, indicating spring germination. Similar to J. atratus, daily temperature fluctuations did not control germination at suitable microsites. In Cnidium dubium that occurs at higher elevated sites, the level of primary dormancy of seeds was sufficient to prevent germination following dispersal, but the level was dependent on the year of harvest. Buried seeds showed an annual dormancy/conditional dormancy cycle. Dormancy was only partially broken by cold–wet stratification. It was completely broken by application of a high concentration of gibberellic acid. C. dubium had no absolute light requirement for germination, but it was stimulated by high light levels and in contrast to the other two species, seeds were stimulated by daily temperature fluctuations. Germination would therefore be maximized by gaps in early spring when the flooding water has receded. Re-entering dormancy in the late spring fails to support that germination occurs immediately after early-summer mowing – an important factor at subcontinental flood meadows.

Morphophysiological dormancy in seeds of six endemic lobelioid shrubs (Campanulaceae) from the montane zone in Hawaii

The purpose of this study was to investigate seed dormancy breaking and germination requirements of six woody Hawaiian endemic lobelioids (Campanulaceae). Seeds of all species had underdeveloped, physiologically dormant embryos and thus morphophysiological dormancy. Fresh seeds of Clermontia pyrularia Hillebr. and Trematolobelia macrostachys (Hook. & Arnott) A. Zahlbr. did not germinate during 4 weeks of incubation in light at 15/6, 20/10, or 25/15 °C, whereas those of Clermontia fauriei H. Lev., Clermontia hawaiiensis (Hillebr.) Rock, Clermontia kakeana Meyen, and Cyanea angustifolia (Cham.) Hillebr. germinated to 61%–85% but only at 25/15 °C. Since seeds of the latter four species eventually germinated to 84%–100% when incubated for 12–36 weeks at the three temperature regimes, fresh seeds had conditional dormancy; the physiological component of morphophysiological dormancy was nondeep. Seeds of Trematolobelia macrostachys also came out of dormancy (and germinated to 90%) during 18 weeks of incubation at each of the three temperatures regimes, whereas those of Clermontia pyrularia did so only at 15/6 °C. Simulated seasonal temperature variations did not promote dormancy break and germination in any species except Clermontia pyrularia , in which a 12-week incubation period at 25/15 °C resulted in 90% germination after seeds were moved to 20/10 °C. Seeds of all species had an absolute light requirement for germination except those of Clermontia pyrularia, which germinated to 48% in darkness. Since seeds of the six species only require high temperatures for embryo growth and the breaking of physiological dormancy, they have nondeep simple morphophysiological dormancy.

Seed germination and propagation of Xyris tennesseensis, a federal endangered wetland species

Abstract The recovery plan for the U.S. federally endangered Xyris tennesseensis calls for increasing the size of some existing populations and establishing new ones in suitable sites. As a contribution to this goal, we investigated seed dormancy and germination and attempted to propagate the species in non-native soil. Freshly matured seeds were conditionally dormant and germinated to 0, 0, 92, 91, and 74% in light after two weeks at 15/6, 20/10, 25/15, 30/15, and 35/20°C, respectively. Seeds retained the ability to germinate to 80–100% in light at 25/15 and at 30/15°C throughout a 39.5-month period of burial in an unheated greenhouse. Following the first year of burial, however, germination at 20/10°C showed an annual cycle, with 79–86% of the seeds germinating in spring but only 0–1% in autumn. Under natural temperature regimes, seeds sown on native soil germinated from mid-May to early August. Seeds had an absolute light requirement for germination, and those incubated at 30/15°C required six days of ...

Effect of light and its interaction with nitrate and ammonium ions in seed germination of Caesulia axillaris

Seeds of Caesulia axillaris Roxb. displayed an absolute light requirement for germination throughout the period of dry storage at 28°C. The seeds were found to show a gradual increase in percent germination with storage time ‐ reaching a maximum value between 8‐14 months and then a sharp decline. Percent water uptake and photosensitivity were at maximum after a 5‐day imbibition period in the dark in both seedlots studied. Seedlot I, which was only marginally responsive to far‐red light, showed a nearly complete red‐far‐red reversal effect in contrast to seedlot II. The latter also displayed a considerable promotion of germination in far‐red light. Interestingly, a noticeable degree of heterogeneity, besides the one observed in both seedlots with reference to red light, was found to exist in seedlot II for far‐red light. Exogenous application of nitrate and ammonium, at the levels occurring in soil during seed germination/seedling emergence phase of the plant in nature, promoted a considerable proportion of high Ø‐requiring seeds to germinate under irradiation conditions establishing low Ø‐value. The probable ecological implication of this reponse has been discussed. Little correlation was found between the requirement for an exogenous supply of nitrate and the endogenous nitrate level in the seeds in their response to far‐red light.

Dormancy, Germination and Mortality of Seeds in a Chalk-Grassland Flora

SUMMARY (1) Seeds of thirteen herbaceous species from chalk grassland in The Netherlands were buried in their natural habitat. Samples were exhumed at regular intervals over 3 years. Mortality and germination in situ were recorded. The surviving seeds were tested for germination in light and darkness and with different temperature regimes. (2) Seed mortality was low, except in Gentianella germanica and Origanum vulgare. In Carlina vulgaris, Leontodon hispidus and Scabiosa columbaria disappearance of seeds was mainly caused by germination in the soil. (3) Freshly harvested seeds of Arenaria serpyllifolia and Linum catharticum had an absolute light requirement for germination which was retained during burial. Burial induced a light requirement for germination in Origanum vulgare. (4) All species that germinated showed some degree of primary dormancy and seasonal change in secondary dormancy. This was most pronounced in shortlived species. (5) The seasonal change in secondary dormancy of surviving seeds was most evident either from germinability in light (Arenaria, Daucus carota and Linum), in darkness ( Carlina, Leontodon, Plantago lanceolata and Scabiosa), or both (Centaurea scabiosa). The response of the seeds to temperature also varied seasonally. (6) The amplitude of seasonal change in dormancy tended to decrease during the 3-year of burial in some species (Arenaria, Linum and Daucus). (7) Rhinanthus minor and R. alectorolophus seeds only germinated in late winter and were dormant during the remainder of the year.

Role of temperature, light and date: seeds were exhumed from soil on germination of four wetland perennials

Seeds of the four wetland perennials Cyperus odoratus L., Gratiola viscidula Pennell, Penthorum sedoides L. and Scirpus lineatus Michx. were buried in soil and exposed to yearly seasonal temperature cycles. At monthly intervals for 30.5 or 31 months, seeds were exhumed and tested at daily alternating (12/12 h) temperature regimes of 15/6, 20/10, 25/15, 30/15 and 35/20°C in light (14 h photoperiod) and darkness. Seeds of all species had an absolute light requirement for germination. Freshly matured seeds of C. odoratus and P. sedoides were conditionally dormant, while those of G. viscidula and S. lineatus were dormant. Seeds of all species became non-dormant during winter; however, those of C. odoratus and G. viscidula never gained the ability to germinate at 15/6°C. Buried seeds of C. odoratus and P. sedoides remained non-dormant during the remainder of the study, while those of G. viscidula and S. lineatus exhibited an annual conditional dormancy/non-dormancy cycle.

Dormancy, germination and mortality of seeds in heathland and inland sand dunes

SUMMARY Seeds of seven dominant species from heathland and inland sand dunes were buried in their natural habitat and exhumed twice a year, in March and September, during a 2- or 3-year period. The number of dead, germinated and surviving seeds was recorded and the latter were subjected to a germination test in a fluctuating temperature regime of 12/22°C in light. All the seeds of Deschampsia flexuosa had germinated in situ within 6 months of burial. This was also the case for almost all seeds of Agrostis vinealis and the majority of the seeds of Corynephorus canescens; the remaining seeds survived until the end of the experiment (2 years). About 35% of the seeds of Molinia caerulea died or germinated in situ; the remaining seeds survived until the end of the experiment (3 years) and showed a seasonal pattern of changing dormancy that has been described for many summer annuals. Dormancy in the soil is enforced by a requirement for temperature fluctuation. The winter annual Spergula morisonii showed a dormancy pattern which was typical for that life form, i.e. alleviation of dormancy in summer and induction of dormancy during winter. The two dwarf shrubs Calluna vulgaris and Erica tetralix had an absolute light requirement for germination and no seeds germinated in the soil during the 3 years; the mortality of C. vulgaris was low, whereas 40% of the E. tetralix seeds died. No seasonal change in dormancy was detected in either species.

Sequential Photoregulation of Fern-Spore Germination

Summary Spores of Dryopteris filix-mas have an absolute light requirement for germination, which is mediated by phytochrome. The effect of a single red pulse 24 h after sowing is potentiated by a light pretreatment, given before the spores acquire competence to P fr . This pretreatment (the inducing effect of which is abolished by a far-red pulse) can consist of a single pulse as well; P fr has to be present for several hours, and is most effective towards the end of the pretreatment period. The effect does not require the maximum possible P fr level, and even a level of 10–20% P fr /P tot can significantly enhance the result of the subsequent inducing pulse. Generally, the pretreatment effect is greatest, if the inducing pulse is given with a non-saturating fluence or with a wavelength establishing an intermediate P fr level. It is assumed, and will be tested in future experiments, that P fr resulting from both pretreatment and inducing pulses act upon the same system, and that their products add to each other to surpass a threshold allowing germination.

Effect of storage, photoperiod and mechanical scarification on seed germination in Ocimum americanum

Seeds of Ocimum americanum L. display an absolute light requirement for germination. The minimal length of the daily photoperiod required to induce a high germination decreased with increasing seed age, but the length of the photoperiod under potential control of terminal far‐red light inhibition remained unchanged. There was a gradual escape from the far‐red inhibition with increase in the length of the photoperiod. Seeds developed flash photosensitivity after the first 13 h photoperiod. Scarification treatment did not allow the seeds to bypass the light requirement, but it enhanced the germination considerably. Under conditions of natural day length in the field, weakening of the testa by sand may abolish the need for a second exposure to light for most of the seed population, thus rendering them non‐photoperiodic.