Soil warming increases plant species richness but decreases germination from the alpine soil seed bank

Global warming is occurring more rapidly above the treeline than at lower elevations and alpine areas are predicted to experience above average warming in the future. Temperature is a primary factor in stimulating seed germination and regulating changes in seed dormancy status. Thus, plant regeneration from seed will be crucial to the persistence, migration and post disturbance recruitment of alpine plants in future climates. Here, we present the first assessment of the impact of soil warming on germination from the persistent alpine soil seed bank. Contrary to expectations, soil warming lead to reduced overall germination from the soil seed bank. However, germination response to soil temperature was species specific such that total species richness actually increased by nine with soil warming. We further explored the system by assessing the prevalence of seed dormancy and germination response to soil disturbance, the frequency of which is predicted to increase under climate change. Seeds of a significant proportion of species demonstrated physiological dormancy mechanisms and germination of several species appeared to be intrinsically linked to soil disturbance. In addition, we found no evidence of subalpine species and little evidence of exotic weed species in the soil, suggesting that the soil seed bank will not facilitate their invasion of the alpine zone. In conclusion, changes in recruitment via the alpine soil seed bank can be expected under climate change, as a result of altered dormancy alleviation and germination cues. Furthermore, the alpine soil seed bank, and the species richness therein, has the potential to help maintain local species diversity, support species range shift and moderate species dominance. Implications for alpine management and areas for further study are also discussed.     

Predicted global warming scenarios impact on the mother plant to alter seed dormancy and germination behaviour in Arabidopsis

Abstract Seed characteristics are key components of plant fitness that are influenced by temperature in their maternal environment, and temperature will change with global warming. To study the effect of such temperature changes, Arabidopsis thaliana plants were grown to produce seeds along a uniquely designed polyethylene tunnel having a thermal gradient reflecting local global warming predictions. Plants therefore experienced the same variations in temperature and light conditions but different mean temperatures. A range of seed‐related plant fitness estimates were measured. There were dramatic non‐linear temperature effects on the germination behaviour in two contrasting ecotypes. Maternal temperatures lower than 15–16 °C resulted in significantly greater primary dormancy. In addition, the impact of nitrate in the growing media on dormancy was shown only by seeds produced below 15–16 °C. However, there were no consistent effects on seed yield, number, or size. Effects on germination behaviour were shown to be a species characteristic responding to temperature and not time of year. Elevating temperature above this critical value during seed development has the potential to dramatically alter the timing of subsequent seed germination and the proportion entering the soil seed bank. This has potential consequences for the whole plant life cycle and species fitness.     

Climate warming could shift the timing of seed germination in alpine plants

Background and Aims

Despite the considerable number of studies on the impacts of climate change on alpine plants, there have been few attempts to investigate its effect on regeneration. Recruitment from seeds is a key event in the life-history of plants, affecting their spread and evolution and seasonal changes in climate will inevitably affect recruitment success. Here, an investigation was made of how climate change will affect the timing and the level of germination in eight alpine species of the glacier foreland.

Methods

Using a novel approach which considered the altitudinal variation of temperature as a surrogate for future climate scenarios, seeds were exposed to 12 different cycles of simulated seasonal temperatures in the laboratory, derived from measurements at the soil surface at the study site.

Key Results

Under present climatic conditions, germination occurred in spring, in all but one species, after seeds had experienced autumn and winter seasons. However, autumn warming resulted in a significant increase in germination in all but two species. In contrast, seed germination was less sensitive to changes in spring and/or winter temperatures, which affected only three species.

Conclusions

Climate warming will lead to a shift from spring to autumn emergence but the extent of this change across species will be driven by seed dormancy status. Ungerminated seeds at the end of autumn will be exposed to shorter winter seasons and lower spring temperatures in a future, warmer climate, but these changes will only have a minor impact on germination. The extent to which climate change will be detrimental to regeneration from seed is less likely to be due to a significant negative effect on germination per se, but rather to seedling emergence in seasons that the species are not adapted to experience. Emergence in autumn could have major implications for species currently adapted to emerge in spring.     

Climate change and bet-hedging: interactions between increased soil temperatures and seed bank persistence

In order to predict the long-term consequences of climate change, it is necessary to link future environmental changes to mechanisms that control plant population processes. This information can then be incorporated into strategies to more accurately model climate change impacts on species or to estimate future extinction risks. We examined the impact of increased temperatures on the longevity and dynamics of the persistent soil seed banks of eight ephemeral species from arid Australia. We found that the predicted global temperature increases under climate change will be reflected in increased soil temperatures, and that seeds in the soil seed bank will be exposed to long durations of high temperatures over the summer months. Three of the eight species studied had significantly greater levels of germination after exposure to predicted increased soil temperatures. Another species displayed a dramatic decrease in seed viability after such exposure. The capacity of such species to use the seed bank to bet hedge against rainfall events that cause germination but are insufficient to allow plant maturation, is compromised by increased germinability and subsequent loss or reduction of seed bank persistence. These predicted changes in the dynamics of soil seed banks increase the risk of local extinctions of these species, while the composition of the community may be altered by changes in species abundance. Our results show that the risk spreading mechanism provided by persistent seed banks could be compromised by the mechanistic impact of forecast temperature increases in arid habitats, and highlight the need to understand mechanisms that control population dynamics when attempting to address likely future impacts of climate change on biodiversity.     

Impacts of growth form and phylogenetic relatedness on seed germination: A large‐scale analysis of a subtropical regional flora

Plant regeneration strategy plays a critical role in species survival and can be used as a proxy for the evolutionary response of species to climate change. However, information on the effects of key plant traits and phylogenetic relatedness on seed germination is limited at large regional scales that vary in climate. To test the hypotheses that phylogenetic niche conservatism plays a critical force in shaping seed ecophysiological traits across species, and also drives their response to climatic fluctuation, we conducted a controlled experiment on seed germination and determined the percentage and rate of germination for 249 species in subtropical China under two temperature regimes (i.e., daily 25°C; daily alternating 25/15°C for each 12 hr). Germination was low with a skewed distribution (mean = 38.9% at 25°C, and 43.3% at 25/15°C). One fifth of the species had low (<10%) and slow (4–30 days) germination, and only a few (8%) species had a high (>80%) and rapid (1.2–6.6 days) germination. All studied plant traits (including germination responses) showed a significant phylogenetic signal, with an exception of seed germination percentage under the alternating temperature scenario. Generalized linear models (GLMs) and phylogenetic generalized estimation equations (GEEs) demonstrated that growth form and seed dispersal mode were strong drivers of germination. Our experimental study highlights that integrating plant key traits and phylogeny is critical to predicting seed germination response to future climate change.     

Dormancy and germination: making every seed count in restoration

From 50 to 90% of wild plant species worldwide produce seeds that are dormant upon maturity, with specific dormancy traits driven by species' occurrence geography, growth form, and genetic factors. While dormancy is a beneficial adaptation for intact natural systems, it can limit plant recruitment in restoration scenarios because seeds may take several seasons to lose dormancy and consequently show low or erratic germination. During this time, seed predation, weed competition, soil erosion, and seed viability loss can lead to plant re‐establishment failure. Understanding and considering seed dormancy and germination traits in restoration planning are thus critical to ensuring effective seed management and seed use efficiency. There are five known dormancy classes (physiological, physical, combinational, morphological, and morphophysiological), each requiring specific cues to alleviate dormancy and enable germination. The dormancy status of a seed can be determined through a series of simple steps that account for initial seed quality and assess germination across a range of environmental conditions. In this article, we outline the steps of the dormancy classification process and the various corresponding methodologies for ex situ dormancy alleviation. We also highlight the importance of record‐keeping and reporting of seed accession information (e.g. geographic coordinates of the seed collection location, cleaning and quality information, storage conditions, and dormancy testing data) to ensure that these factors are adequately considered in restoration planning.     

Seasonal rhythms of seed rain and seedling emergence in two tropical rain forests in southern Brazil

Seasonal tropical forests show rhythms in reproductive activities due to water stress during dry seasons. If both seed dispersal and seed germination occur in the best environmental conditions, mortality will be minimised and forest regeneration will occur. To evaluate whether non-seasonal forests also show rhythms, for 2 years we studied the seed rain and seedling emergence in two sandy coastal forests (flooded and unflooded) in southern Brazil. In each forest, one 100 x 30-m grid was marked and inside it 30 stations comprising two seed traps (0.5 x 0.5 m each) and one plot (2 x 2 m) were established for monthly monitoring of seed rain and a seedling emergence study, respectively. Despite differences in soil moisture and incident light on the understorey, flooded and unflooded forests had similar dispersal and germination patterns. Seed rain was seasonal and bimodal (peaks at the end of the wetter season and in the less wet season) and seedling emergence was seasonal and unimodal (peaking in the wetter season). Approximately 57% of the total species number had seedling emergence 4 or more months after dispersal. Therefore, both seed dormancy and the timing of seed dispersal drive the rhythm of seedling emergence in these forests. The peak in germination occurs in the wetter season, when soil fertility is higher and other phenological events also occur. The strong seasonality in these plant communities, even in this weakly seasonal climate, suggests that factors such as daylength, plant sensitivity to small changes in the environment (e.g. water and nutrient availability) or phylogenetic constraints cause seasonal rhythms in the plants.     

Seed germination traits of Ailanthus altissima,Phytolacca americana and Robinia pseudoacacia in response to different thermal and light requirements

Invasion of alien plant species (IAS) represents a serious environmental problem, particularly in Europe, where it mainly pertains to urban areas. Seed germination traits contribute to clarification of invasion dynamics. The objective of this research was to analyze how different light conditions (i.e., 12-hr light/12-hr darkness and continuous darkness) and temperature regimes (i.e., 15/6°C, 20/10°C and 30/20°C) trigger seed germination of Ailanthus altissima (AA), Phytolacca americana (PA) and Robinia pseudoacacia (RP). The relationship between seed germination and seed morphometric traits was also analyzed. Our findings highlight that temperature rather than light was the main environmental factor affecting germination. RP germinated at all tested temperatures, whereas at 15/6°C seeds of AA and PA showed physiological dormancy. RP had a higher germination capacity at a lower temperature, unlike AA and PA, which performed better at the highest temperatures. Light had a minor role in seed germination of the three species. Light promoted germination only for seeds of PA, and final germination percentage was 1.5-fold higher in light than in continuous darkness. Seed morphometric traits (thickness [T], area [A] and volume [V]) had a significant role in explaining germination trait variations. The results highlight the importance of increasing our knowledge on seed germination requirements to predict future invasiveness trends. The increase in global temperature could further advantage AA and PA in terms of germinated seeds, as well as RP by enhancing the germination velocity, therefore compensating for a lower germination percentage of this species at the highest temperatures.     

Modelling the potential impact of climate variability and change on species regeneration potential in the temperate forests of South‐Eastern Australia

The sensitivity of early plant regeneration to environmental change makes regeneration a critical stage for understanding species response to climate change. We investigated the spatial and temporal response of eucalypt trees in the Central Highland region of south eastern Australia to high and low climate change scenarios. We developed a novel mechanistic model incorporating germination processes, TACA‐GEM, to evaluate establishment probabilities of five key eucalypt species, Eucalyptus pauciflora, Eucalyptus delegatensis, Eucalyptus regnans, Eucalyptus nitens and Eucalyptus obliqua. Changes to regeneration potential at landscape and site levels were calculated to determine climate thresholds. Model results demonstrated that climate change is likely to impact plant regeneration. We observed increases and decreases in regeneration potential depending on the ecosystem, indicating that some species will increase in abundance in some forest types, whilst other forest types will become inhabitable. In general, the dry forest ecosystems were most impacted, whilst the wet forests were least impacted. We also observed that species with seed dormancy mechanisms, like E. pauciflora and E. delegatensis, are likely to be at higher risk than those without. Landscape‐ and site‐level analysis revealed heterogeneity in species response at different scales. On a landscape scale, a 4.3 °C mean temperature increase and 22% decline in precipitation (predicted for 2080) is predicted to be a threshold for large spatial shifts in species regeneration niches across the study region, while a 2.6 °C increase and 15% decline in precipitation (predicted for 2050) will likely result in local site‐level shifts. Site‐level analysis showed that considerable declines in regeneration potential for E. delegatensis, E. pauciflora and E. nitens were modelled to occur in some ecosystems by 2050. While overall model performance and accuracy was good, better understanding of effects from extreme events and other underlying processes on regeneration will improve modelling and development of species conservation strategies.     

Cracking the case: Seed traits and phylogeny predict time to germination in prairie restoration species

Traits are important for understanding how plant communities assemble and function, providing a common currency for studying ecological processes across species, locations, and habitat types. However, the majority of studies relating species traits to community assembly rely upon vegetative traits of mature plants. Seed traits, which are understudied relative to whole‐plant traits, are key to understanding assembly of plant communities. This is particularly true for restored communities, which are typically started de novo from seed, making seed germination a critical first step in community assembly and an early filter for plant establishment. We experimentally tested the effects of seed traits (mass, shape, and embryo to seed size ratio) and phylogeny on germination response in 32 species commonly used in prairie grassland restoration in the Midwestern USA, analyzing data using time‐to‐event (survival) analysis. As germination is also influenced by seed dormancy, and dormancy break treatments are commonly employed in restoration, we also tested the effects of two pretreatments (cold stratification and gibberellic acid application) on time to germination. Seed traits, phylogeny, and seed pretreatments all affected time to germination. Of all traits tested, variables related to seed shape (height and shape variance) best predicted germination response, with high‐variance (i.e., pointier and narrower) seeds germinating faster. Phylogenetic position (the location of species on the phylogenetic tree relative to other tested species) was also an important predictor of germination response, that is, closely related species showed similar patterns in time to germination. This was true despite the fact that all measured seed traits showed phylogenetic signal, therefore phylogeny provided residual information that was not already captured by measured seed traits. Seed traits, phylogenetic position, and germination pretreatments were important predictors of germination response for a suite of species commonly used in grassland restoration. Shape traits were especially important, while mass, often the only seed trait used in studies of community assembly, was not a strong predictor of germination timing. These findings illustrate the ecological importance of seed traits that are rarely incorporated into functional studies of plant communities. This information can also be used to advance restoration practice by guiding restoration planning and seed mix design.     

Engineering seed dormancy by the modification of zeaxanthin epoxidase gene expression

Abscisic acid (ABA) is a plant hormone synthesized during seed development that is involved in the induction of seed dormancy. Delayed germination due to seed dormancy allows long-term seed survival in soil but is generally undesirable in crop species. Freshly harvested seeds of wild-type Nicotiana plumbaginifolia plants exhibit a clear primary dormancy that results in delayed germination, the degree of primary dormancy being influenced by environmental culture conditions of the mother plant. In contrast, seeds, obtained either from ABA-deficient mutant aba2-s1 plants directly or aba2-s1 plants grafted onto wild-type plant stocks, exhibited rapid germination under all conditions irrespective of the mother plant culture conditions. The ABA biosynthesis gene ABA2 of N. plumbaginifolia, encoding zeaxanthin epoxidase, was placed under the control of the constitutive 35S promoter. Transgenic plants overexpressing ABA2 mRNA exhibited delayed germination and increased ABA levels in mature seeds. Expression of an antisense ABA2 mRNA, however, resulted in rapid seed germination and in a reduction of ABA abundance in transgenic seeds. It appears possible, therefore, that seed dormancy can be controlled in this Nicotiana model species by the manipulation of ABA levels.     

Soil burial induced dormancy in weedy rice seeds through hormone level changes: Implications in adaptive evolution and weed control

Seed dormancy plays a key role in preventing seeds of higher plants from random germination under adverse environmental conditions. Previous studies suggested that a critical temperature could regulate germination of weedy rice seeds without primary dormancy at seed dispersion. However, what will happen to the non-dormant seeds after shattering in the soil seed banks when temperature fluctuates to exceed the critical temperature remains an interesting question to be investigated. To determine whether or not soil burial can change the status of dormancy in weedy rice seeds, we examined germination ratios of weedy rice seeds after soil-burial treatments. In addition, we compared hormone levels in the untreated seeds and viable but ungerminated seeds after soil burial. Results showed that soil burial induced a proportion of 41%–72% dormant seeds in the initially non-dormant weedy rice seeds. Also, the induction of seed dormancy is associated with the change of hormone levels in the seeds treated by soil burial, suggesting that soil burial can significantly activate the control of hormone production in seeds. Together, the previously reported mechanism of critical temperature-inhibited seed germination and the newly found phenomenon of soil burial-induced seed dormancy provide a “double-security” strategy to ensure germination of weedy rice seeds under a favorable condition in agricultural ecosystems. The findings not only reveal the important role of rapid evolution of adaptive functions in weeds, such as weedy rice, in adapting to changing agricultural environments, but also facilitate the design of strategies for effective weedy rice control practices.     

Hidden biodiversity in the Arctic – a study of soil seed banks at Disko Island,Qeqertarsuaq, West Greenland

Seed dispersal is a key process in plant community dynamics, and soil seed banks represent seed dispersal in time rather than in space. Despite their potential importance, seed bank dynamics in the Arctic are poorly understood. We investigated soil seed banks and corresponding plant community composition in three contrasting vegetation types in West Greenland, viz. dwarf shrub heaths, herb slopes and fell‐fields. Through germination testing, 31 species were documented in soil seed banks. All of these were herbaceous, while no dwarf‐shrub species, which represents the dominating growth form in the above‐ground vegetation, were emerging from the seed bank. Consequently, across vegetation types, the lowest similarity between seed bank and above‐ground vegetation was found in dwarf shrub heath. Nine plant species were exclusively found in seed bank, all of which were non‐clonal forbs. Seed bank size (total number of seeds) and species richness seemed to increase with the level of natural disturbance. Additionally, we examined the effect of different experimental light and temperature conditions on the quantity and diversity of germinating seeds. The difference in diversity in vegetation and seed bank at the species level will impact population dynamics, regeneration of vegetation after disturbances and its potential to respond to climate change.     

光信号与激素调控种子休眠和萌发研究进展

休眠是种子植物在长期进化过程中产生的适应性性状, 通过抑制种子在不适宜的环境中萌发进而保证植物能够在逆境中生存。此外, 休眠有助于种子的长距离运输和扩散, 因此休眠对种子延续和物种保存具有重要意义。种子由休眠向萌发的发育转变不仅关系到物种的繁衍, 而且对保证农业生产中作物的产量和品质也具有重要作用。种子的休眠和萌发受到内源激素和外源光信号的共同调控。其中, 外源光信号主要通过调控内源ABA和GA的生物合成及信号转导进而调控种子休眠和萌发。该文系统综述了外源光信号和内源激素调控种子休眠和萌发的作用通路以及两类信号通路之间的交互作用, 旨在为农业生产中利用光和激素调控种子休眠与萌发提供参考。     

光信号与激素调控种子休眠和萌发研究进展

休眠是种子植物在长期进化过程中产生的适应性性状, 通过抑制种子在不适宜的环境中萌发进而保证植物能够在逆境中生存。此外, 休眠有助于种子的长距离运输和扩散, 因此休眠对种子延续和物种保存具有重要意义。种子由休眠向萌发的发育转变不仅关系到物种的繁衍, 而且对保证农业生产中作物的产量和品质也具有重要作用。种子的休眠和萌发受到内源激素和外源光信号的共同调控。其中, 外源光信号主要通过调控内源ABA和GA的生物合成及信号转导进而调控种子休眠和萌发。该文系统综述了外源光信号和内源激素调控种子休眠和萌发的作用通路以及两类信号通路之间的交互作用, 旨在为农业生产中利用光和激素调控种子休眠与萌发提供参考。     

Temperature thresholds of physically dormant seeds and plant functional response to fire: variation among species and relative impact of climate change

Variation in dormancy thresholds among species is rarely studied but may provide a basis to better understand the mechanisms controlling population persistence. Incorporating dormancy‐breaking temperature thresholds into existing trait frameworks could improve predictions regarding seed bank persistence, and subsequently species resilience in response to fire, climate change and anthropogenic management. A key ecological strategy for many species from fire‐prone ecosystems is the possession of a long‐lived seed bank, ensuring recovery after fire. Physical dormancy is dominant in these ecosystems and maintaining this dormancy is directly linked to seed bank persistence. We identified a suite of seed‐related factors relevant to maintaining populations in fire‐prone regions for 14 co‐occurring physically dormant species. We measured variation in initial levels of dormancy and then applied experimental heating treatments, based on current seasonal temperatures and those occurring during fires, to seeds of all study species. Additionally, higher seasonal temperature treatments were applied to assess response of seeds to temperatures projected under future climate scenarios. Levels of germination response and mortality were determined to assess how tightly germination response was bound to either fire or seasonal cues. Six species were found to have dormancy cues bound to temperatures that only occur during fires (80°C and above) and were grouped as having obligate pyrogenic dormancy release. The remaining species, classified as having facultative pyrogenic dormancy, had lower temperature dormancy thresholds and committed at least 30% of seeds to germinate after summer‐temperature treatments. Evidence from this study supports including dormancy‐breaking temperature thresholds as an attribute for identifying functional types. High temperature thresholds for breaking dormancy, found in our obligate pyrogenic group, appear to be a fire‐adapted trait, while we predict that species in the facultative group are most at risk to increased seed bank decay resulting from elevated soil temperatures under projected climate change.     

Dormancy and germination: How does the crop seed decide?

Whether seeds germinate or maintain dormancy is decided upon through very intricate physiological processes. Correct timing of these processes is most important for the plants life cycle. If moist conditions are encountered, a low dormancy level causes pre‐harvest sprouting in various crop species, such as wheat, corn and rice, this decreases crop yield and negatively impacts downstream industrial processing. In contrast, a deep level of seed dormancy prevents normal germination even under favourable conditions, resulting in a low emergence rate during agricultural production. Therefore, an optimal seed dormancy level is valuable for modern mechanised agricultural systems. Over the past several years, numerous studies have demonstrated that diverse endogenous and environmental factors regulate the balance between dormancy and germination, such as light, temperature, water status and bacteria in soil, and phytohormones such as ABA (abscisic acid) and GA (gibberellic acid). In this updated review, we highlight recent advances regarding the molecular mechanisms underlying regulation of seed dormancy and germination processes, including the external environmental and internal hormonal cues, and primarily focusing on the staple crop species. Furthermore, future challenges and research directions for developing a full understanding of crop seed dormancy and germination are also discussed.     

生物土壤结皮对种子萌发和幼苗建植的影响研究进展

生物土壤结皮（BSC）在陆地生态系统中具有重要的生态地位,尤其是旱地生态系统中,BSC占据了种子植物之间的广阔地面。因此,BSC的发展必然影响种子植物更新过程与植被空间格局;但其作用方式、影响程度等因相关研究涉及多气候要素、土壤类型、BSC组成物种和种子植物物种的差异及其不同组合,导致目前的研究结论存在广泛争议。研究综合论述了BSC改变地表微形态对种子传播过程的影响;BSC改变土壤特性（物理、化学、生物学）对种子萌发和幼苗存活与建植等关键环节的影响;并结合种子形态特征及种子萌发、幼苗建植的性状等,综合分析了BSC对种子传播、种子萌发与幼苗建植等更新过程的潜在影响机理;探讨了目前研究矛盾性结论产生的原因。总体来说,深入研究并全面揭示BSC对种子植物更新过程的影响,应加强学科交叉,将分子生物学、植物生理学、生物化学等微观研究,与遥感、野外生态因子过程监测、控制实验等宏观、中观研究结合,从机理到过程方面动态研究BSC对种子植物更新过程的影响,并引入水文模型、气候模型、种群动态模型等模型预测方法,研究气候变化、各类干扰频发的情景下,BSC对种子传播、萌发及幼苗建植过程的潜在影响,以期促进对BSC与种子植物间相互关系的研究,加深对干旱脆弱生态系统植被发展规律的认识。     

Is the endangered Apium repens (Jacq.) Lag. rare because of a narrow regeneration niche?

The conservation of rare plant species is an important aspect of global biodiversity protection, but in many cases these species and the reasons why they are rare are poorly understood. The perennial umbellifer Apium repens is generally regarded to be a rare species all over its European range. We hypothesized that its rarity might be caused by a restricted regeneration niche, that is, highly specific requirements for sexual regeneration, low seed dispersal potential and low endurance capacity of seeds in the ground. We conducted several experimental investigations on its germination ecology, hydrochorous dispersal potential and soil seed bank properties. Apium repens showed high germination success under a variety of abiotic conditions. Either light or cold-wet stratification was necessary to stimulate germination. Seeds were able to float for more than 50 days when protected from precipitation, and soil seed bank sampling revealed that at least some seeds of A. repens were contained in soil depths of up to 10 cm. Overall, our findings do not support the hypothesis that the rarity of A. repens is caused by highly specific requirements for its sexual regeneration. Nonetheless, its germination ecology should be considered when designing conservation measures for this endangered species.     

Ethylene in seed dormancy and germination

The role of ethylene in the release of primary and secondary dormancy and the germination of non-dormant seeds under normal and stressed conditions is considered. In many species, exogenous ethylene, or ethephon – an ethylene-releasing compound - stimulates seed germination that may be inhibited because of embryo or coat dormancy, adverse environmental conditions or inhibitors (e.g. abscisic acid, jasmonate). Ethylene can either act alone, or synergistically or additively with other factors. The immediate precursor of ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid (ACC), may also improve seed germination, but usually less effectively. Dormant or non-dormant inhibited seeds have a lower ethylene production ability, and ACC and ACC oxidase activity than non-dormant, uninhibited seeds. Aminoethoxyvinyl-glycine (AVG) partially or markedly inhibits ethylene biosynthesis in dormant or non-dormant seeds, but does not affect seed germination. Ethylene binding is required in seeds of many species for dormancy release or germination under optimal or adverse conditions. There are examples where induction of seed germination by some stimulators requires ethylene action. However, the mechanism of ethylene action is almost unknown.
The evidence presented here shows that ethylene performs a relatively vital role in dormancy release and seed germination of most plant species studied.