Differences In Germination Responses Research Articles

Among- and within-population variation in germination response shapes ecological resilience in the Mediterranean cliff species Brassica incana Ten.

Understanding how plant species respond to extreme conditions is crucial for predicting their ecological resilience under climate change. Here, we aim to forecast the ecological resilience of the Mediterranean cliff species Brassica incana (Brassicaceae) by estimating population variation in germination response under novel extreme environmental conditions. We investigated the thermal germination responses in 14 populations of B. incana by exposing seeds to temperatures within and outside conditions experienced in their local environment. Then, we quantified among- and within-population variation in germination response to extreme temperatures, estimated genotype-by-environment interactions (G × E) and tested if population performance at extreme temperatures is explained by local climate. We found significant among-population differences in germination response, a different level of within-population variability, and different mechanisms underlying G × E patterns. Also, populations experiencing warmer temperatures in their local environment showed a better performance at both cold and hot extremes while populations experiencing colder temperatures showed a limited ability to germinate under extreme conditions. Our results suggest that populations experiencing warmer temperatures in their local environment have a higher potential to face future thermal extreme conditions and their role is thus crucial to promote species ecological resilience.

Differences in germination response to temperature, salinity, and water potential among Prosopis laevigata populations are guided by the tolerance-exploitation trade-off.

Exploring the mechanisms that promote population divergence represents a central point in evolutionary ecology. Along their distribution, species commonly experience contrasting environmental conditions, which impose local selection pressures to which populations tend to adapt resulting, for example, in ways to deal with resource shortage or abundance. In this study, we explored if germination performance varies under different levels of temperature, water potential and salinity among populations of Prosopis laevigata, a widespread mesquite species from the arid and semi-arid zones of Mexico. Given the wide distribution of P. laevigata and the sensitivity of the germination phase to environmental conditions, we hypothesized the existence of differential responses during this crucial stage of plant development. Thus, we expected germination in populations of P. laevigata from more arid zones to be less sensitive to high temperatures, salinity, and water deficit. Also, we explored if the exploitation–tolerance trade-off guides the differentiation of P. laevigata populations in germination performance under varying conditions. Germination of all populations was very sensitive to water scarcity but not to variation in temperature or salinity. We identified two major axes of trait covariation in germination physiology: one defined by tolerance of germination to water and saline stress versus germination velocity, and the other defined by the tolerance to extreme temperatures. We found evidence that variation in tolerance among the populations was related with their distribution along environmental gradients. Overall, populations with a higher capacity to germinate under water deficit stress, salinity, and extreme temperatures inhabit warmer and more saline areas. Our study provides strong evidence of existing local adaptations during germination of P. laevigata from across its distribution in the arid lands of Mexico.

Variation in the seasonal germination niche across an elevational gradient: the role of germination cueing in current and future climates.

The timing of germination has profound impacts on fitness, population dynamics, and species ranges. Many plants have evolved responses to seasonal environmental cues to time germination with favorable conditions; these responses interact with temporal variation in local climate to drive the seasonal climate niche and may reflect local adaptation. Here, we examined germination responses to temperature cues in Streptanthus tortuosus populations across an elevational gradient. Using common garden experiments, we evaluated differences among populations in response to cold stratification (chilling) and germination temperature and related them to observed germination phenology in the field. We then explored how these responses relate to past climate at each site and the implications of those patterns under future climate change. Populations from high elevations had stronger stratification requirements for germination and narrower temperature ranges for germination without stratification. Differences in germination responses corresponded with elevation and variability in seasonal temperature and precipitation across populations. Further, they corresponded with germination phenology in the field; low-elevation populations germinated in the fall without chilling, whereas high-elevation populations germinated after winter chilling and snowmelt in spring and summer. Climate-change forecasts indicate increasing temperatures and decreasing snowpack, which will likely alter germination cues and timing, particularly for high-elevation populations. The seasonal germination niche for S. tortuosus is highly influenced by temperature and varies across the elevational gradient. Climate change will likely affect germination timing, which may cascade to influence trait expression, fitness, and population persistence.

Seed germination in tailings cake and cake-reclamation substrate mixtures with oil sands process water

We investigated the germination of 13 species commonly used in oil sands mining reclamation of boreal forest as influenced by substrate type (potting soil, tailings cake and mixtures of cake-sand, cake-peat and cake-forest floor mineral mix (FFMM)) and water quality (0, 50 and 100% oil sands process water). Germination responses clustered into three groups with trees and graminoids exhibiting the highest germination (84-99%), followed by shrubs and forbs with intermediate germination (46-69%), and the native forb species, Chamerion angustifolium, Achillea millefolium and Galium boreale, with the lowest germination (7-18%). Among substrates, potting soil supported the highest germination (69%), followed by cake mixed with peat (64%) or FFMM (63%), cake-sand (60%) and cake (57%). Concentrations of ions, e.g. sodium and chloride, were higher in cake and cake-sand than in cake-peat or cake-FFMM suggesting that mixing cake with FFMM or peat can alleviate salt stress and encourage germination. Process water had little or no effect on germination especially on cake and cake amendments possibly due to the high ionic content of these substrates. There were major differences in germination response among species. Trees and graminoids may be well suited for reclaiming oil sands tailings whereas native forbs may perform poorly when used for revegetating tailings.

Differences in germination response to smoke and temperature cues in ‘pyrophyte’ and ‘pyrofuge’ forms of Erica coccinea (Ericaceae)

Many plants in fire-prone ecosystems produce seeds that are cued to germinate after fire. However, fire is not uniform in the landscape, and there are often refugia where fire does not reach, like rocky outcrops or moist valleys. Erica coccinea, a heath shrub from the South African fynbos, has two distinct pyrophyte forms (a resprouter and a seeder) as well as a ‘pyrofuge’ form that only occurs in fire refugia. We measured germination response to smoke and incubation temperature in seeds from pyrophyte (resprouter and seeder) and pyrofuge populations to determine whether these forms responded differently to a fire-cue (smoke) and a general germination cue (temperature). We found that seeds from pyrofuge plants had high germination success (80.9–92.0%) at the lowest incubation temperature (15/8°C 12h day/night cycle) regardless of smoke exposure. In contrast, seeds from pyrophytes (resprouters and seeders) responded strongly to the smoke cue (71.2–95.0%) and were not as limited by temperature. These results show that fire presence and absence is driving divergence of the primary germination cue in Erica coccinea. Given the patchiness of many natural fire regimes worldwide, we expect there may be pyrofuge populations exhibiting a similar divergence of traits in other species and other fire-prone ecosystems.

Influence of altitude on local adaptation in upland tree species from central Argentina.

Steep climatic gradients boost morphological and physiological adjustments in plants, with consequences on performance. The three principal woody species of the Sierras Grandes Mountains of central Argentina have marked differences in sapling performance along their altitudinal distribution. We hypothesize that the steep gradient of climatic conditions across the species' altitudinal distribution promotes trait differences between populations of different altitudes that are inherited by the following generation. Seeds from different altitudes were exposed to three temperature regimes to assess differential germination responses. Saplings were then transplanted to a greenhouse to assess possible variations in attributes and performance after 18 months. The three species showed differences in germination responses to temperature among altitudes and/or in sapling attributes and performance. In Maytenus boaria and Escallonia cordobensis, germination success was higher under high temperatures for the highest-altitude, whereas lower temperatures boosted germination of the lowest altitudes. Polylepis australis showed no differences in germination among temperature treatments. In the greenhouse, saplings of the three species from intermediate altitudes showed high performance, whereas the upper and lower populations seemed to be adjusted to tolerating more stressful conditions (i.e., lower temperatures at the upper end and water stress at the lower end), showing lower performance toward both altitudinal limits. These patterns agree with those described for saplings growing under field conditions, suggesting adjustments in response to environmental changes undergone by populations along the altitudinal range. The marked adjustments of populations to the local environment suggest a potentially high impact of climatic change on species distribution.

Mass-based germination dynamics of Rudbeckia mollis (Asteraceae) seeds following thermal and ageing stress

AbstractSeed mass is an important plant functional trait linked to germination. For instance, higher-mass seeds often display greater germination compared to lower-mass seeds when exposed to non-stressful conditions. Yet, knowledge pertaining to germination dynamics for different mass-based seed fractions following exposure to abiotic stress is lacking. Here, we assess the germination response of relatively fresh, mass-separated Rudbeckia mollis (Asteraceae) seeds to various simulated seasonal temperatures, supra-optimal temperatures and increasing ageing stress duration. Air density separation yielded three mass-based classes, called light (393 ± 35 μg), intermediate (423 ± 29 μg) and heavy (474 ± 38 μg). Water uptake kinetics indicated that imbibition (0–6 h) and germination lag (6–24 h) were independent of seed mass. Similarly, germination and viability loss of fresh seeds following exposure to seasonal and supra-optimal constant temperatures were independent of mass. However, seed mass influenced germination following increasing ageing stress, with light seeds germinating to a significantly greater extent than intermediate or heavy seeds. For example, final germination per cent in light-class seeds was about 1.7 times greater than intermediate or heavy seeds after 20 d of saturated salt accelerated ageing (SSAA). Seeds stored for 1 year in the laboratory displayed mass-dependent germination patterns similar to seeds following SSAA. Mass-independent germination responses may be a strategy to maintain an annual life history in otherwise difficult environments when R. mollis seeds are relatively fresh. However, differences in germination response between aged and unaged seeds suggest that mass-dependent viability loss may occur in R. mollis.

Maternal temperature effects on dormancy influence germination responses to water availability in Arabidopsis thaliana

With climate change, germination cuing to water availability is expected to be especially important for seedling survival. Here, we examined germination responses to low water potential and tested whether dormancy status mediates these responses. We considered both genetically based dormancy (genotypes with allelic variation in dormancy genes) as well as dormancy imposed by the environment (low seed-maturation temperature or short duration of dry afterripening). We examined (a) germination capacity at low water potential, (b) germination acceleration in response to pre-incubation at low water potential, and (c) secondary dormancy induction by low water potential. We found that both environmentally imposed dormancy and genetically based dormancy influenced germination responses to low water potential. Specifically, dormancy established via introgression of a strong dormancy allele and dormancy induced by low seed-maturation temperatures both reduced the ability to germinate at low water potential. Pre-incubation at low water potential accelerated germination, but the rate differed between both dormancy-inducing environments and among dormancy genotypes. Prolonged incubation at low water potential induced secondary dormancy, and this effect was greater in fresher (more dormant) seeds and in seeds that were matured at low temperature (a dormancy-inducing treatment). Although genotypes also varied in secondary dormancy induction, their level of primary dormancy did not predict their induction into secondary dormancy. Environmentally induced dormancy also influenced the expression of genetic differences in germination responses to low water potential. Thus environmentally determined dormancy influences not only germination responses to low water potential but also their evolutionary potential.

Temperature and drought drive differences in germination responses between congeneric species along altitudinal gradients

Temperature and drought effects on germination were explored by comparing species from above and below the treeline of the Central Alps. This study should enhance the understanding of species recruitment under changing environmental conditions. The timing of germination, final germination percentage, and optimum temperature of 14 congeneric species pairs were investigated. We hypothesized that (i) temperature will affect the timing of germination, with species above the treeline having a more rapid germination time; (ii) final germination percentage (FGP) will be generally enhanced by higher temperatures; (iii) species below the treeline will have wider temperature ranges and will be more adapted to drought; (iv) species above the treeline will have higher optimum temperatures of germination, and (v) seed mass will affect the germination rates. Germination experiments were carried out using alternating temperature regimes (25°/10 °C, 20°/10 °C, 15°/5 °C) and decreasing water potentials (−0.3, −0.6, −0.9 MPa), generated using polyethylene glycol. Temperature significantly affected the timing and FGP; species above the treeline exhibited a delayed timing at lower temperatures and a generally lower FGP at all temperature regimes in contrast to their congeners below the treeline. The optimum germination temperatures were significantly higher for species above the treeline. Five of 28 species did not germinate at all. Drought generally affected all species; however, the negative response of the species above the treeline was more pronounced. The seed mass did not affect the FGP. We conclude that the germination traits of the species above the treeline may have major disadvantages in a changing climate, resulting in a weaker performance and delayed growth, whereas the species below the treeline may be considered pre-adapted for potential migration to higher altitudes.

Using thermal time models to predict germination of five provenances of silver birch (<i>Betula pendula</i> Roth) in southern England

Climate predictions indicate that growing conditions may become unfavourable for certain tree species in parts of Britain. Guidelines suggest some planting of seed sources from regions between 2° and 5° south of those currently used as part of a climate change adaptation strategy. However, there has been little research on the benefits and risks associated with the use of planting stock from more southerly seed sources. Seeds of five provenances of the ‘relatively’ dormant were germinated over a range of temperatures both with and without a pre-chill. Subsequently, a thermal time model was used to predict the impact of migrating these provenances to southern England. Results identified geographical differences in germination response; those from higher latitude were more sensitive to pre-chill.Betula pendula

An evaluation of germination efficiency in a range of genotypes of Thymus species differing in susceptibility to drought

The aim of this study was to compare the germination of a range of Thymus genotypes subjected to different levels of drought stress, in order to identify differences in germination response to water stress, important to inform plant breeders aiming to produce more drought tolerant crops. Germination is the first, and arguably the most important and vulnerable stage in the life cycle of plants. Thymus spp seeds from a range of genotypes were germinated under four external osmotic potentials (0, -2, -4 and -6 Bar) imposed using appropriate concentrations of PEG6000. Following 10 days of exposure to drought, fresh weight, dry weight, radicle and plumule length, water content, percentage germination and germination time were recorded. There was considerable variation between the genotypes in their response to drought. Under mild stress (-2 bar) T. serpyllum and T. vulgaris (Iran) were more tolerant than other varieties. However, under moderate stress (-4 bar), T. serpyllum (Spain) was the most tolerant. Under -6 bar (severe stress), T. vulgaris (Spain), T. zygis (Spain) and T. kotchyanous (Iran) were scored as tolerant.

Temperature regulates positively photoblastic seed germination in four ficus (moraceae) tree species from contrasting habitats in a seasonal tropical rainforest

Differences in seed germination responses of trees in tropical forests to temperature and light quality may contribute to their coexistence. We investigated the effects of temperature and red:far-red light (R:FR ratio) on seed germination of two gap-demanding species (Ficus hispida and F. racemosa) and two shade-tolerant species (F. altissima and F. auriculata) in a tropical seasonal rainforest in southwest China. A R:FR ratio gradient was created by filtering fluorescent light through polyester filters. Four temperature treatments were used to test the effect of temperature on seed germination of the four Ficus tree species across the R:FR gradient. Seeds of the four Ficus species were positively photoblastic. Seed germination of F. hispida and F. racemosa was not affected across the R:FR ratio gradient (0.25-1.19) at 25/35°C, but it was inhibited under low R:FR at 22/23°C. By contrast, germination percentages of F. altissima and F. auriculata were not inhibited along the entire light gradient in all temperature treatments. Differences in germination responses of Ficus species might contribute to differences in their habitat preferences. The inhibitory effect of understory temperatures in the forest might be a new mechanism that prevents positively photoblastic seeds of the gap-demanding species such as F. hispida and F. racemosa from germinating in the understory and in small canopy gaps.

English

Rapid and uniform seedling growth is a pre-requisite for better establishment of oil palm plantations. Chemical pretreatments can be used to increase the rate and uniformity of seed germination. Thiamethoxam and imidacloprid are insecticides classified in the broad-spectrum systemic neonicotinoid group and their use in seed treatment has been claimed to increase seed germination and vigor in some crops. Thiamethoxam at the rate of 0, 0.1, 0.3, 0.6 and 0.9 g ai. L-1 of water and imidacloprid at the rate of 0, 0.2, 0.5, 0.9 and 1.4 g ai. L-1 of water were evaluated using dry-heated seed (seed with 18% moisture content heated at 40°C for 60 days) to observe the differences in germination response and seedling vigor. The results revealed that imidacloprid at the rate of 0.5 g ai. L-1 of water significantly increased shoot length while thiamethoxam did not. Both neonicotinoids did not affect the germinated seed percentage, the time taken to reach 50% germination (T50) and root length. It can be concluded that imidacloprid could increase seedling vigor by stimulating the shoot growth of dry-heated oil palm seed. No phytotoxicity of thiamethoxam and imidacloprid following dry-heated seed germination was observed. Key words: Thiamethoxam, imidacloprid, germination, seedling vigor, tenera oil palm seed.

SKRINING UNTUK TOLERANSI TERHADAP STRES KEKERINGAN PADA 36 VARIETAS KEDELAI PADA FASE PERKECAMBAHAN

Water stress due to drought is the most significant abiotic factor limiting crop growth and development. Drought stress inhibit germination and seedling growth, and extention of inhibition in germination under drought stress condition is varying in varieties. The previous research result showed that the differences in germination response under drought stress can be used as early test for screening to drought tolerance in plants. The objectives of this experiment were to evaluate the germination response of 36 soybean varieties under drought stress simulated by polyethylene glycol (PEG), to know the drought-stress tolerance level of 36 soybean varieties based on germination response in medium containing PEG, and to identify drought tolerant varieties. Soybean seeds were germinated in sand medium containing several PEG (6000) at concentration 0%, 15% and 20% which equivalent to 0, -0,41 and -0,67 MPa during 5 days. Germination responses were observed by calculating vigor index, germination percentage, lateral root number and measuring hypocotyl and root lenght and seedling dry weight. The level of drought stress tolerance of soybean varieties were evaluated based on index of reduction and drought sensitivity on germination variables in stres and non-stres conditions. The research result showed that drought stress on germination media simulated by PEG decreased vigor index, germination percentage, lateral root number, hypocotyl and root lengths and dry weight of seedling. The inhibition of germination increased with reduction of water potential. The water potential -0,41 MPa inhibited vigor index and hypocotyls length in all tested varieties, but inhibited germination percentage, lateral root number and dry weight of seedling in some varieties. However, decreasing of water potential -0,67 MPa inhibited almost germination variables in all varieties, except root length. Each tested soybean variety showed differences of germination response to drought stres. Varieties of Dieng, Tidar and Sibayak showed less inhibition than others, but Anjasmoro, Burangrang, Galunggung, Kipas Putih and Tambora showed more inhibition in seedling growth. Based on index of reduction and drought sensitivity on germination variables, Dieng and Tidar were identified as tolerant varieties, while sixteen varieties as medium tolerant and seventeen varieties as sensitive ones.

Effects of waterlogging on seed germination of three Mediterranean oak species: Ecological implications

Soil water saturation during prolonged periods of time generates a negative impact on nearly all terrestrial plants. In Mediterranean woodlands, precipitation can be very abundant during the wet season, inducing temporary soil waterlogging, coinciding with the seed dispersal and germination time of many species. We investigated the effects of waterlogging on seed germination and early root growth of three coexisting oak species ( Quercus canariensis, Q. suber and Q. pyrenaica), by completely flooding of seeds for various periods of time. The three oak species showed a certain level of tolerance to waterlogging, only being affected those seeds subjected for long periods of submersion (over 30 days). Waterlogging during prolonged periods of time decreased the probability of seed germination in the three oak species, lengthened the time to germination, and hampered root development in two of the studied species. The main differences between oak species occurred in terms of root growth ( Q. canariensis being the less affected, and Q. suber the most); these differential responses could be related to a species rank of waterlogging tolerance. Thus inter-specific differences in germination responses to waterlogging could contribute to explain, at least partially, species habitat and distribution patterns across landscapes. Seed mass also played an important role on different aspects of germination, though its relative importance varied as function of species and waterlogging treatment. The tolerance to stress induced by waterlogging increased with seed mass, but only in the case of Q. canariensis.

Does post-fire plant regeneration mode affect the germination response to fire-related cues?

Vegetative resprouting, soil or canopy-stored seed banks, post-fire seed dispersal and germination are the major strategies by which plants regenerate after fires. Post-fire regeneration modes of plants are commonly based on the presence or absence of post-fire recruitment as well as the presence or absence of post-fire resprouting. High temperatures, smoke and ash are characteristics of fire and the post-fire environment. We hypothesized that heat, smoke, ash and pH will have differential effects on seed germination depending on species' post-fire regeneration strategies: serotinous vs. nonserotinous (which may have soil seed banks) and resprouters vs. nonresprouters (which may be obligate seeders). Here we examined the effects of these factors on the germination of 27 common east Australian species. Most serotinous species supported our hypothesis by showing no effect or reduced germination in response to heat. However, contrary to our prediction, all nonserotinous nonresprouting species also showed no effect or reduced germination in response to heat. Smoke, contrary to our hypothesis, had a negative or no effect on all serotinous and nonresprouting species, but no clear directional effect on serotinous and resprouting species. Supporting our hypotheses, ash and high pH showed positive or nonsignificant effects on the germination of all serotinous resprouting species, and a negative or no effect on nonserotinous resprouting species. However, contrary to our prediction, it had a negative or no effect on the serotinous nonresprouting species and no clear effect on nonserotinous nonresprouting species. We also discovered large differences in germination responses between conspecific populations that varied in their degree of resprouting. Although our data confirmed several of our predictions, the overall conclusion is that the responses of seeds to heat, smoke, ash and pH are not tightly associated with post-fire regeneration functional types.

The germination characteristics of Scrophularia marilandica L. (Scrophulariaceae) seeds

Investigations on seeds of Scrophularia marilandica L. were undertaken to determine their germination requirements. Seeds were collected from three naturally occurring sites and one greenhouse-grown population in London, Ontario in September and October of 1997. Some were set to germinate immediately after collection; others were stored in or on soil outside and/or under controlled laboratory conditions before testing. Germination was assessed under two light/temperature regimes (35°C 14 h light, 20°C 10 h dark and 25°C 14 h light, 10°C 10 h dark), in continuous darkness, and in the presence of two germination-promoting chemicals (GA3 and KNO3). Fresh seeds germinated best at 35/20°C, while stored seeds germinated best at 25/10°C. No differences in percent germination were found among three seed-maturity stages. All chemical treatments, except 0.01 M KNO3, increased percent germination. Significant differences were found both among and within sites for most chemical treatments, but exposure to 3 × 10−4 M GA3 caused almost every seed to germinate. When compared to the control, both the gibberellic acid and the soil-storage treatments contributed to faster germination. Exposure of seeds to naturally prevailing conditions on the soil surface followed by testing under the 25/10°C regime produced the highest percent germination. No seeds germinated in the dark. In summary, seeds of S. marilandica exhibit physiological dormancy, which can be alleviated by exposure to light, after-ripening and/or cold stratification. It is probable that the differences in germination response among sites can be attributed to differences in environmental conditions during seed production. These experiments indicate that the seeds of S. marilandica must be buried shortly after dispersal in order to form a persistent seed bank.

Comparisons of germination traits of alpine plants between fellfield and snowbed habitats

AbstractWe examined the seed‐germination responses of 27 alpine species with reference to habitat type (fellfield and snowbed), temperature (five regimes), and light requirement. About 70% of species showed >40% germination at warm temperatures without cold stratification. However, a moist‐chilling treatment markedly improved the germination percentages in most species, especially under cool conditions. Thus, cold stratification effectively reduced the temperature requirement for germination. Patterns of germination response within species were not consistent between the fellfield and snowbed habitats for species inhabiting both habitats. For interspecific comparisons, there were no significant differences in germination responses to the temperature regimes and the cold stratification between the fellfield and snowbed species. Also, germination speed and the length of germinating period did not differ between fellfield and snowbed species. Most species (86%) showed a requirement for light for germination without cold stratification. Although the extent of the light requirement was reduced after cold stratification in some species, the light requirement of most small‐seeded species remained. The combination of cold stratification and the light requirement is a major factor determining the seedling emergence and formation of seed banks in alpine plants. However, habitat‐specific patterns of germination traits were less clear, suggesting similar germination traits in fellfield and snowbed plants, at least under controlled conditions in the laboratory.

Use of the hydrothermal time model to analyse interacting effects of water and temperature on germination of three grass species

The temperate grass species, red fescue (Festuca rubrassp.litoralis), perennial ryegrass (Lolium perenne) and Kentucky bluegrass (Poa pratensis), are often sown in mixtures for turfgrass. Differences in germination response to environmental conditions often result in different establishment success. The three species were compared in a study of imbibition at reduced water potential (Ψ) and in a study of the effects of Ψ and temperature on germination. In all three species, imbibition rate and extent were reduced with decreasing Ψ, causing a prolonged lag-phase before germination, particularly in Kentucky bluegrass. In perennial ryegrass and Kentucky bluegrass, water content at radicle emergence decreased non-linearly with decreasing Ψ, with a lower asymptote expressing the critical water content for germination. Seeds were germinated in factorial combinations of two temperatures (10 and 25°C) and nine Ψ levels (–2 to 0 MPa). Kentucky bluegrass required a longer thermal time to germinate than the other species and exhibited conditional dormancy at 25°C, which affected the use of the thermal time model. The effects of Ψ were described by a hydrotime model. Kentucky bluegrass had higher base water potential (Ψb) and required a longer hydrotime for germination than the other species. However, Ψbincreased with temperature in Kentucky bluegrass and red fescue, but decreased in perennial ryegrass, and the base temperatures also changed with Ψ. The interacting effects of Ψ and temperature affected the ability of the hydrothermal time model to predict germination performance across all temperature and Ψ conditions.

Seasonal changes in the germination responses of Hordeum maritimum and H. murinum seeds in relation to salinity, temperature and after‐ripening time

The effects of temperature and salinity (NaCl) on germination of Hordeum maritimum With, (halophyte) and H. murinum L. (glycophyte) seeds were investigated. Dehulled caryopses were used for monthly germination trials, starting from November (120 days of after‐ripening in darkness at 20±1°C). Trials were continued for one year. Differences in germination response between the two species were observed, confirming that H. Maritimum is better adapted to high salinity levels and to variations in external temperature than H. murinum. H. maritimum showed a germination control mechanism related to after‐ripening time and based on seed dormancy break/resumption. At higher temperature (30°C), thermodormancy was also recorded. No germination strategies were observed in H. murinum that is relatively insensitive to the combined effects of temperature and salinity. Thus, in virtually all treatments, H. murinum exhibited a higher germination rate compared with H. maritimum, as early as 72 h after imbibition, suggesting that dormancy, both in the presence or absence of salt, is totally abolished by early fall or at the latest in winter.