Germination 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.

For seed banks showing seasonal changes in their dormancy level, the possibility of predicting temporal patterns of emergence depends on establishing a robust relationship between temperature and the rate of dormancy loss and induction. However, although the effect of temperature on dormancy loss has been extensively studied, less work has been advocated to the quantification of temperature effects on dormancy induction. In the present work, we quantified temperature regulation of dormancy induction in Polygonum aviculare seeds using the hydrotime model. To study induction into secondary dormancy, seeds previously released from primary dormancy through stratification at 5°C were stored at dormancy-inductive temperatures of 10, 15, 20 and 25°C for different periods. During storage, seeds were germinated at different temperatures and water potentials, and hydrotime model parameters were derived. Changes in hydrotime model parameters (mean base water potential for germination and its standard deviation, and the hydrotime required for germination) during dormancy induction were described by adjusting exponential equations. Obtained results indicated a minimum temperature for dormancy induction of 8.7°C and the existence of a bi-linear relationship between rate of induction into secondary dormancy and storage temperature, in which storage temperatures around 25°C showed a higher dormancy induction rate than those below 20°C. Developed model equations were then used to predict changes in germination behaviour during dormancy induction at different temperatures, showing a good agreement between simulated and observed values.

The influence of acid scarification on the responsiveness of curly dock (Rumex crispus L. ♯ RUMCR) seeds to physical and chemical factors was studied. Scarification made the seeds responsive to GA4+7 (a mixture of gibberellin A4 + A7) and markedly improved the responsiveness to light, moist-chilling, and a 1-h 40-C temperature shift. Scarification reduced the mechanical restraint of the seedcoat by 0.4 to 0.8 MPa. Removal of the entire pericarp induced 69% germination in the dark. Moist-chilling treatment of seeds reduced the soaking period needed for maximum response to the high-temperature shift from 24 to 6 h. The embryo growth potential generated by moist-chilling was less in magnitude than that by the reduction in seed coat restraint by scarification. Induction of secondary dormancy was prevented to a marked degree in scarified (chilled or unchilled) seeds during polyethylene glycol-6000 (PEG) treatment in light or in the presence of GA4+7 while intact seeds rapidly became secondarily dormant in light. The ability of scarified seeds to remain germinable or nondormant for a longer period than the intact seed in low water potential imbibing medium may be due to a net reduction (by 0.4 to 0.8 MPa) in the impact on the embryo of germination-preventing forces (low water potential plus mechanical restraint of the seed coat).

Laboratory experiments were conducted to determine the effect of light, oxygen, and submergence on bur beggarticks seed germination. Fresh and dry stored seeds exhibited dormancy, requiring thiourea and light for germination. Red light was more effective than far-red or blue light in breaking dormancy. Both an oxygen-saturated and anoxic atmosphere completely inhibited germination. Hypoxic conditions (5 and 10% oxygen) led to an increase in germination compared to normoxia (21% oxygen). Primary dormancy was eliminated by 1 yr of soil burial. Seeds exhumed after soil burial had greater germination percentage than fresh or lab-stored seeds after a brief far-red irradiation, but did not germinate in the dark. The induction of secondary dormancy increased with increasing durations of submergence. Finally, sowing at different soil depths (0 to 8 cm) showed that germination and emergence occurred mainly with shallow burial (0.5 to 1.0 cm).

Survival and dormancy of purple nutsedge tubers has not been studied quantitatively. Yet this is fundamental to our understanding of the population dynamics of this highly noxious weed. Field studies were conducted to determine the effect of age on tuber survival and dormancy. A modified exponential decay function accurately described the age-dependent decline in tuber survival. This model is biologically meaningful, has good statistical properties, and can describe a wide range of responses. Tuber population half-life was 16 mo, and the predicted longevity (99% mortality) was 42 mo. Burial depth at 8 and 23 cm had no significant effect on survival or dormancy. Tuber dormancy increased with age. After 18 mo, the proportion of dormant tubers in the surviving population was two-and-one-half times higher than in the 3-mo-old population. We report for the first time that tubers were able to enter a state of secondary dormancy after sprouting. The finding that tubers persist after sprouting has important implications for population dynamics of this species. This is also the first report of tuber predation by the larvae of a billbug.

To understand persistence strategies of meadow and western salsify, ecophysiological characteristics of their seed germination were studied. Anaerobiosis (immersion in deoxygenated water) induced secondary dormancy in seeds of both species. Dormancy could be induced in 86% of meadow salsify seeds and in 65% of western salsify seeds by a 1-d anaerobiosis treatment. The induced dormancy was gradually released during storage of air-dried secondary dormant meadow salsify seeds, and the rate of this release was influenced by storage temperature; 30 C was more effective than 10 or 20 C in releasing secondary dormancy. These results suggest that the two species may rely on induced dormancy as an option in their persistence strategy. The optimum temperature for germination of nondormant seeds of both species was 15 C. Maximum germination percentages for both species were established within 4 to 6 d of incubation at 15 C and within 14 to 28 d of incubation at 25 C. Nondormant seeds did not germinate below 10 or above 30 C. Stratification (at 5 C for 2 to 10 wk) stimulated germination of secondary dormant seeds of meadow salsify. This stratification requirement can be important in preventing germination of dormant salsify seeds in the fall, thereby avoiding high seedling mortality in the winter. Light (red and far-red) had no effect on germination of seeds in secondary dormancy. In a separate study, seeds of both species were planted in pots at depths of 2 to 14 cm and seedling emergence was observed. Maximum emergence occurred when seeds were buried 2 cm deep. Seeds planted 8 cm or deeper germinated but did not emerge.

Seed deterioration, and therefore seed germination potential, are highly influenced by relative humidity and temperature. However, limited species-specific information is available about the effect of long-term soaking in water on seed germination potential. Knowing the potential fate of a creeping bentgrass seed that falls in an irrigation canal is important for the study of transgene flow in this species at the landscape level. The objectives of this study were to evaluate the effect of soaking time and water temperature on germination of creeping bentgrass seed and to assess how fast a panicle could be moved in an irrigation canal. Germination was determined for seeds from panicles of three cultivars of creeping bentgrass that were soaked in water for up to 17 wk at two water temperatures, 4 and 20 C. Creeping bentgrass seeds did not lose their ability to germinate after 17 wk in water at 20 C and, although reduced, germination was still 46% after 17 wk in water at 4 C. The reduction in germination in seeds from panicles kept in water at 4 C was due to the induction of secondary dormancy, which was overcome by dry seed storage at room temperature. We quantified that a panicle that falls in an irrigation canal has the potential to travel downstream at an average rate of 19 m min−1 and move seeds that could potentially establish seedlings elsewhere. Therefore, movement of creeping bentgrass seed by water has to be considered as a means of gene flow.

Seedbank persistence in canola seeds is related to their potential to develop secondary dormancy. This can result in volunteer weed problems many years after canola production. The potential to be induced into secondary dormancy is controlled by both the canola genetics and the environment of the mother plant. However, the effect of time of harvesting on secondary dormancy potential is not known. The objective of this study was to determine the effect of harvest timing on potential to develop seed dormancy in canola. Six harvest samples were collected weekly from two canola genotypes (5440 and 5020) starting from 10 to 20% seed color change on the main stem until they were fully ripened. Freshly harvested seeds of 5440 and 5020 showed 13 and 16% primary dormancy at 32 and 33 d after flowering (DAF), respectively, but dormancy decreased with harvest timings and no dormancy was observed when seeds were fully mature (78 DAF). After dormancy induction, 10% of 5440 seeds were dormant at 32 DAF, but 94% of seeds were dormant at 78 DAF. Similarly, 70% of 5020 seeds were dormant at 33 DAF, but 90% of seeds were dormant at 68 DAF. Thus, seeds had lower potential to secondary dormancy at early development but have a high potential to secondary dormancy induction at full maturity. This study suggests that windrowing these canola genotypes at the recommended time (60% seed color change on the main stem) may reduce ability of the seed to develop secondary dormancy and thus reduce the persistence of seeds in the soil seedbank.

In western Canada, little is known about the seedbank ecology of volunteer canola. Therefore, integrated recommendations for the management of this weed are limited. In this study, we investigated the seedbank persistence and seedling recruitment of two spring canola genotype groups with different secondary seed dormancy potentials under contrasting tillage systems. The study was conducted at two locations with different soils in the Mixed Moist Grassland ecoregion of Saskatchewan. A single cohort seedbank was established in 1999 and was followed for 3 yr in successive wheat crops. In a separate laboratory study, the six canola genotypes examined were classified as those with high and those with medium potentials for the development of secondary seed dormancy (HD and MD, respectively). After one, two, and three winters, maximum persistence of 44, 1.4, and 0.2% of the original seedbank was observed among the treatments, respectively. In 2001, HD canola genotypes tended to exhibit 6- to 12-fold greater persistence than MD canola genotypes, indicating lower seedbank mortality in HD canola. Seedling recruitment of HD canola also was higher than MD canola when differences were observed between these genotype groups. Therefore, long-term seedbank persistence of canola can be reduced by growing genotypes with low inherent potential for the development of secondary seed dormancy. The proportion of persisting seeds tended to be higher under conventional tillage than under zero tillage because of lower seedbank mortality, but no clear distinction in seedbank persistence in terms of absolute time could be made between these two tillage systems. Volunteer canola seedling recruitment followed the pattern of a typical summer-annual weed, where seedling emergence was observed only during May and June.

The involvement of environmental factors in dormancy cycling is well known in temperate annual species, but it is not known how interaction between soil temperatures and humidity can modulate dormancy in perennial tropical species. In this study the effects were evaluated of substrate temperature and humidity on the modulation of the acquisition and overcoming of secondary dormancy in the buried seeds of two endemic Eriocaulaceae species from the rocky fields (campos rupestres) vegetation in south-eastern Brazil. Fresh seeds of Comanthera bisulcata and Syngonanthus verticillatus were buried and subsequently maintained at temperatures of 15, 20, 25 and 30°C, under three substrate humidity levels (boggy, humid and humid/dry). The seeds were exhumed every 3 months and tested for germination (20°C, 12 h photoperiod) and viability (tetrazolium test). The seeds of both species acquired dormancy after burial in all of the treatments. During the experimental period they demonstrated cycles of acquisition and overcoming of dormancy that were most evident in the treatments involving alterations of the substrate humidity (humid/dry regime) that coincided with the environmental conditions found naturally in the region of origin of the species. The seeds gradually lost dormancy during the dry period and re-acquired it when exposed again to humidity; dormancy would once again be overcome during the subsequent dry period. Burial promoted the acquisition of dormancy in C. bisulcata and S. verticillatus seeds; the lowest temperature tested favoured overcoming dormancy; and varying the humidity regime signalled the acquisition and the overcoming of secondary dormancy.

Seeds can synchronize their germination and dormancy cycles to regular seasonal environmental changes. The present work sought to evaluate the in-situ longevity of the buried seeds of two species of Syngonanthus and two species of Comanthera (Eriocaulaceae) in the region of natural occurrence (Serra do Cipó Range, south-eastern Brazil), and to relate their germination responses to seasonal climatic changes. Samples were exhumed bimonthly and germination was tested under a 12-h photoperiod (30 μmol m− 2s− 1) at optimal germination temperature. The seeds of Comanthera showed high deterioration after the first year of burial, especially C. elegans, which reflects their incapacity to form viable soil seed banks. The buried seeds of C. bisulcata, S. anthemidiflorus and S. verticillatus acquired secondary dormancy during the rainy season (spring/summer, higher temperatures) which was alleviated during the subsequent dry season (autumn/winter, lower temperatures). It is concluded that C. bisulcata, S. anthemidiflorus, and S. verticillatus form seed banks of the persistent type and demonstrate consecutive cycles of germination/dormancy, accompanying annual seasonal changes for at least 2 years.

Secondary dormancy is predominantly associated with seed behaviour in soil seed banks. Periodic changes in secondary dormancy may explain seasonal emergence of weedy species. Temperature and possibly soil water potential appear to be the predominant factors that determine the annual cycling of dormancy. Dormancy cycling is paralleled by modulations of germination responsiveness to germination stimulants, such as light and nitrate and to the width of the germination temperature window. Membranes have been proposed to be the primary target for the perception of temperature. It is hypothesized that alterations in properties of cellular membranes are involved in the regulation of dormancy. Possible mechanisms are discussed.

Imbibed embryos of after-ripened and secondarily thermo- and FR-dormant Agrostemma githago seeds were investigated as to their ability to synthesize DNA, RNA and proteins with the aim of finding characteristic differences connected with the induction and maintenance of developmental arrest. A gradual decrease in DNA synthesis was observed during the induction of thermodormancy. However, DNA synthesis was stimulated up to that of embryos of 30–h-imbibed after-ripened seeds within 24 h approximately after transferring the thermodormant seeds into temperatures which normally allow germination. DNA synthesis of embryos of FR-dormant seeds remained constant at a relatively low level during 7 d FR and another 7 d dark incubation. RNA synthesis decreased to different extents during induction of thermo- and FR-dormancy when it was arrested at a relatively low level in seeds transferred to temperatures which normally allow germination. Processes leading to an increase in RNA synthesis such as in embryos of after-ripened seeds appeared to be quantitatively and/or qualitatively repressed. Interestingly, protein synthesis was extremely depressed during induction of thermodormancy whereas it was slightly stimulated during induction of FR-dormancy. Nevertheless two-dimensional protein PAGE revealed several polypeptides which were new, increased, decreased or not synthesized predominantly in axes of thermo- and FR-dormant seeds in comparison to germinating after-ripened seeds. It is suggested that a connection exists between these polypeptides and the repression of germination. After transferring seconarily dormant seeds to temperatures which normally allow germination, a temporary stimulation of protein synthesis could be observed in both cases.

To colonize newly disturbed areas, weedy species must disperse their seeds in space and/or in time. Cirsium vulgare has poor dispersal in space, but can form a persistent seed bank. Fresh seeds are capable of germinating in either light/dark or constant dark conditions under favourable diurnal temperatures of 25°C: 10°C. Despite this lack of dormancy, a large proportion of seeds do not germinate in the autumn after dispersal. Variation in germination requirements according to seed colour was also examined. Fresh seeds were placed under one of two overwintering treatments at 5°C, alternating light/dark or constant darkness. Some seeds of all colours: white, light, intermediate, dark and black germinated under these conditions. Six months later, ungerminated seeds subjected to the light/dark treatment did not require light for germination when placed under optimal temperatures. However, most seeds that had overwintered in constant darkness required light for germination. In the field, this induced dormancy would prevent seeds from germinating if buried or located in deep shade. Such seeds have the potential of forming a persistent seed bank. The proportion of dormant seeds did not appear to be associated with seed colour. Seeds incubated at 10°C following overwintering under light/dark conditions germinated to a higher percentage than seeds overwintered in darkness, regardless of the light conditions for germination. The results of this study help to explain the contradiction between delayed germination in the field and the lack of seed dormancy.

The effect of flooding on the dormancy level of Setaria parviflora seeds from a non-flooded upland and a seasonally (winter–spring) flooded lowland in the Pampa grasslands of Argentina was investigated. Seeds from both communities were subjected to reciprocal burial treatments in the two habitats, and exhumed during and after the flooding season. Effect of immersion in water at 5°C was compared to incubation of seeds on the surface of water-saturated paper at the same temperature. After exhumation of the buried seeds or immersion treatments, germination was assayed at 25°C and at 20/30°C in the dark or in combination with light. Burial in the lowland, which was flooded in winter–spring, significantly reduced germination, while burial in the non-flooded upland did not reduce germination. Similarly, immersion in water at 5°C significantly reduced germination compared to non-immersed controls. During summer, seeds buried in the lowland showed increased capacity to germinate, particularly when exposed to fluctuating temperatures or light. Thus, flooding induced secondary dormancy in S. parviflora seeds, and it was broken during the non-flooding season. These responses of the seeds would prevent germination until there was no further risk of flooding. Remarkably, in S. parviflora seeds harvested from both habitats, we observed essentially the same germination requirements after flooding. However, some slight differences were detected between the seed populations exhumed from the lowland site, indicating that flooding had larger effects on the seeds from the upland community. This suggests some differentiation of these populations evident only after flooding in the field.

The native tobacco, Nicotiana attenuata, synchronizes its germination with the immediate post-fire environment with a combination of germination stimulants found in wood smoke and inhibitors from the unburned litter of the dominant vegetation. The inhibitors override the stimulants and prevent seeds from germinating maladaptively in unburned habitats adjacent to burns. To understand the physiological basis of this environmental control of germination, we tested several previously isolated signals, phytohormones and their respective biosynthesis inhibitors. The germination inhibitors methyl jasmonate (MeJA, a constituent of sagebrush litter), bornane-2,5-dione (BD, a constituent of juniper litter extract, JLE) and JLE did not alter abscisic acid (ABA) content of imbibed seeds. Treatment with the ABA biosynthesis inhibitor, fluridone, inhibited the dormancy-inducing effects of BD, JLE and MeJA, but surprisingly did not affect endogenous ABA levels in treated seeds. However, ABA leached from litter of the species, which dominate the plant community before fires, plays an important role in germination control. We conclude that N. attenuata seeds, which can lie dormant in the soil for 150 years between fires, time their germination with the post-fire environment by responding to smoke, ABA and four terpenes (BD, 1,8-cineole, β-thujaplicin and camphor) leaching from the litter of the dominant vegetation.

Ecophysiological aspects of seed germination were investigated in four Mediterranean geophytes of the genus Muscari (Liliaceae): M. comosum (tassel hyacinth), M. neglectum (common grape hyacinth), M. commutatum and M. weissii. Experiments were performed at constant temperatures in the dark and under temperature and light conditions simulating those prevailing in nature during November–January, i.e. well into the rainy season of the Mediterranean climate. In all species, no primary dormancy was revealed, and germination occurred in a rather narrow range of cool temperatures (optimum at 10 or 15°C) and at a remarkably slow rate; both germination characteristics seem to be associated with autumn/winter seed germination and seedling establishment. Such a postulated strategy is ecologically advantageous within an unpredictable rainfall regime, known to prevail during the start of the rainy period of the Mediterranean climate. This strategy may also explain the spread of germination of M. comosum seeds over two consecutive years, observed by Theophrastus. Far-red light, simulating light conditions under a dense canopy, resulted in only a slight delay of germination compared to dark controls. Diurnal white light, qualitatively simulating natural daylight, caused a significant decrease of the germination rate in all four species studied. Moreover, white light was found to suppress considerably final seed germination (photoinhibition) in M. weissii and M. neglectum; in the latter species, prolonged imbibition under white light also led to the induction of secondary dormancy.