Effect of population, collection year, after-ripening and incubation condition on seed germination of Stipa bungeana

Evaluation of Seed Germination of Six Rare Stipa Species following Low Temperature Stress (Cryopreservation)

Cryopreservation is one way to preserve rare, endangered species. However, during the cryopreservation process, plant cells undergo considerable stress, which may lead to cell death. In our work, orthodox Stipa seeds of six rare species were cryopreserved: S. sareptana, S. ucrainica, S. tirsa, S. dasyphylla, S. adoxa, and S. pulcherríma. Short-term cryopreservation (14 days) stimulated germination of all Stipa species studied. Prolonged cryopreservation (70 days and more) decreased the germination of all Stipa seeds except S. sareptana. The decrease in germination progressed over time as a result of the cumulative stress of cryopreservation rather than the initial stress. To stimulate germination, seeds were stratified and treated with GA3, KNO3, NaOH, and H2O2. After four years of seed cryopreservation, it was possible to obtain seedlings of all the Stipa species studied with 30 days of stratification and 180 days of germination. After five years of cryopreservation and seed treatment with 30% NaOH for one hour, the best germination was obtained in S. adoxa and S. pulcherrima. After treatment with 5% H2O2 for 20 min, the best germination was obtained in S. sareptana, S. ucrainica, and S. dasyphylla. S. sareptana seeds germinated in all the aforementioned experiments. S. sareptana has a non-deep physiological dormancy and is the most widespread and drought-tolerant Stipa species studied. The best habitat adaptation and stress tolerance correlated with this species'cryotolerance. S. sareptana was recommended for further cryopreservation, while storage protocols for the other Stipa species studied need further improvements.

Storage on Maternal Plants Affects Temperature Requirements during Germination in Rumex obtusifolius

Aerial seed banks facilitate population persistence by extending the temporal range of seed dispersal. Knowing the temporal range of germination will improve our understanding of the relationship between seed germination dynamics and aerial seed bank storage duration. We tested the effects of temperature (12/12 h of 5/10, 10/20, 20/30 and 25/35 °C) and light variation (12 h light/12 h darkness and 24 h darkness per day) on germination of Rumex obtusifolius L. seeds retained in an aerial seed bank for 0, 2, 4, 6, 8 and 10 months. Freshly harvested R. obtusifolius were non-dormant and exhibited germination rates of up to 92%. Overall, seeds of R. obtusifolius germinated reliably at all but the lowest temperature (5/10 °C). Seeds maintained high viability throughout the collection period, indicating that fluctuating weather conditions had little influence on seed germination. Thus, the species can maintain viable seeds in aerial storage for up to 10 months and contribute viable seeds to the soil seed bank year-round. This ability to maintain a renewed soil seed bank contributes to the species' strong resilience in colonizing disturbed areas and makes it a difficult weed to control.

Comparison of the effect of temperature and water potential on the seed germination of five Pedicularis kansuensis populations from the Qinghai-Tibet plateau

Temperature and water potentials are considered the most critical environmental factors in seed germinability and subsequent seedling establishment. The thermal and water requirements for germination are species-specific and vary with the environment in which seeds mature from the maternal plants. Pedicularis kansuensis is a root hemiparasitic weed that grows extensively in the Qinghai-Tibet Plateau's degraded grasslands and has seriously harmed the grasslands ecosystem and its utilization. Information about temperatures and water thresholds in P. kansuensis seed germination among different populations is useful to predicting and managing the weed's distribution in degraded grasslands. The present study evaluated the effects of temperature and water potentials on P. kansuensis seed germination in cool and warm habitats, based on thermal time and hydrotime models. The results indicate that seeds from cool habitats have a higher base temperature than those from warm habitats, while there is no detectable difference in optimum and ceiling temperatures between habitats. Seed germination in response to water potential differed among the five studied populations. There was a negative correlation between the seed populations' base water potential for 50% (Ψ _b(50)) germination and their hydrotime constant (θ _H). The thermal time and hydrotime models were good predictors of five populations' germination time in response to temperature and water potentials. Consequently, future studies should consider the effects of maternal environmental conditions on seed germination when seeking effective strategies for controlling hemiparasitic weeds in alpine regions.

Temperature and storage time strongly affect the germination success of perennial Euphorbia species in Mediterranean regions

This study aims to explore the effect of environmental factors (temperature, light, storage time) on germination response and dormancy patterns in eight Mediterranean native wildplants, belonging to the Euphorbia L. genus. In detail, we considered E. amygdaloides subsp. arbuscula, E. bivonae subsp. bivonae, E. ceratocarpa, E. characias, E. dendroides, E. melapetala, E. myrsinites, and E. rigida. We collected seeds from natural plant populations and performed germination assays in climatic chambers at seven constant temperatures (from 5 to 35°C, with 5°C increments), and four fluctuating temperature regimes (8/15, 8/20, 8/25, and 8/30°C, with a 12/12 hr thermoperiod). Germination assays were set up both in dark (D) and in light/dark conditions (L/D, 12/12 hr photoperiod), after short and long seed storage (SS around 30 days and LS around 150 days). For all these species, except E. amygdaloides subsp. arbuscula, results show that the final germinated proportions were improved by a long storage period (>150 days), which supports the existence of nondeep physiological dormancy. Optimal temperature levels ranged from 14.3 to 21.3°C and base temperatures ranged from 5.6 to 12.1°C, while ceiling temperatures from 25.6 to 34.7°C. For none of these species, germinations were favored by an alternating daily temperature regime, while in several instances, germinations were quicker and more complete in darkness, than in an alternating light/dark regime. In some instances, extreme temperature levels (5 and 30°C) induced dormancy and germinations did not resume when seeds were exposed at optimal temperature levels. Results are discussed in terms of the dynamics of emergences and how this might be affected by climate changes.

Seed traits and germination behaviour of four Sardinian populations of Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) along an altitudinal gradient

Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) is an endemic taxon of Sardinia and Corsica, where it grows at different altitudes. The objective of this study was to investigate the seed traits and germination behaviour of four Sardinian populations of this taxon located at different altitudes. Seed traits were evaluated, and germination tests were carried out by incubating seeds at a range of constant (5-30 °C) and alternating (25/10 °C) temperatures. The dry after-ripening (DAR) pre-treatment was also applied by storing seed in dry conditions for 3 months at 25 °C. Seed traits and germination behaviour data were statistically analysed to identify if there was a correlation with altitude. Differences in seed size, area and mass among populations were recorded, however, no relationship was found with altitude. High germination percentages were obtained in all populations, both in untreated and DAR seeds, and were positively affected by alternating temperatures. The final germination percentage and time required to reach 50% final germination (T₅₀ ) showed no relationship with altitude. The differences in seed traits and germination detected among the studied populations of H. microphyllum subsp. tyrrhenicum were not correlated with altitude. This study provides new and important knowledge for this taxon. H. microphyllum subsp. tyrrhenicum is characterised by high germination percentages and low T₅₀ values and does not seem to require any dormancy-breaking treatment. This species represents a high-potential native plant species that should be considered within environmental management plans.

A spatial Markovian framework for estimating regional and local dynamics of annual plants with dormancy

Many species have a dormant stage in their life cycle, including seeds for plants. The dormancy stage influences the species dynamics but is often undetectable. One way to include dormancy is to model it as a hidden dynamical state within a Markovian framework. Models within this framework have already been proposed but with different limitations: only presence/absence observations are modelled, the dormancy stage is limited to one year, or colonisation from neighbouring patches is not taken into account. We propose a hidden Markov model that describes the local and regional dynamics of a species that can undergo dormancy with a potentially infinite dormancy time. Populations are modelled with abundance classes. Our model considers the colonisation process as the indistinguishable influence of neighbour non-dormant population states on a dormant population state in a patch. It would be expected that parameter estimation, hidden state estimation and prediction of the next non-dormant populations would have an exponential computational time in terms of the number of patches. However, we demonstrate that estimation, hidden state estimation and prediction are all achievable in a linear computational time. Numerical experiments on simulated data show that the state of dormant populations can easily be retrieved, as well as the state of future non-dormant populations. Our framework provides a simple and efficient tool that could be further used to analyse and compare annual plants dynamics like weed species survival strategies in crop fields.

Germination characteristics among different sheepgrass (Leymus chinensis) germplasm during the seed development and after-ripening stages

Sheepgrass (Leymus chinensis (Trin.) Tzvel) is an important forage grass in the Eurasian steppe. However, little information is available concerning its seed morphological features and germination characteristics during seed development and after-ripening among different germplasm. To clarify the appropriate seed harvest time and the effects of germplasm, seed development and after-ripening on seed germination, 20 germplasm of sheepgrass were selected. Moreover, the seed morphological and physical changes as well as the seed germination and dormancy characteristics of sheepgrass during seed development stages were analyzed using a seven—d gradient of day after pollination (DAP). The results indicated that the seed water content decreased significantly during 35–42 DAP and that the highest seed germination rate of most germplasm was observed at 35–42 DAP. Thus, 35–42 DAP may be the best time to harvest sheepgrass to obtain the maximum seed germination rate and avoid seed shattering. Furthermore, our results indicated that there were six types of germination patterns, including germplasm with increasing germination rates in the developing seed, such as S19 and S13, and germplasm that maintained a consistently low germination rate, such as S10. Moreover, we compared the seed germination rate of eight germplasm during seed development in both 2016 and 2017, and the results indicated that the seed germination patterns of the eight germplasm were highly consistent between the two consecutive years, suggesting that germplasm rather than year is the major factor in determining germination during seed development. The effect of after-ripening on seed germination was different among the germplasm where four types of germination patterns were revealed for 10 germplasm and resulted in various dormancy features. A two-factor ANOVA analysis suggested that the germplasm of the sheepgrass has a large influence on seed germination, whether during seed development or after-ripening. Thus, these findings lay the foundation for future studies on seed dormancy and germination and may guide the breeding of new cultivars of sheepgrass with better germination performance.

Maintenance of dominant populations in heavily grazed grassland: Inference from a Stipa breviflora seed germination experiment

An understanding of population adaptation and maintenance mechanisms under interference from large herbivores is lacking and is a major focus of ecological research. In the Eurasian steppe, which has been subjected to continuous interference from domesticated ungulates throughout history and shows increased grazing, it is particularly urgent to analyze the ecological adaptation strategies of widely distributed Stipa plants. In this study, Stipa breviflora in a group of desert steppes in the Mongolian Plateau was selected to study the potential mechanism underlying the maintenance of dominant populations under the continuous interference of heavy grazing from the new perspective of seed germination rate. Laboratory experimental results showed that the values of the phenotypic traits of S. breviflora seeds were lower under a heavy grazing treatment than under a non-grazing treatment, but the seed germination rate did not decrease. The awns of non-grazed seeds significantly affected the seed germination rate, while those of heavily grazed seeds did not. Field observations showed that grazing does not significantly affect the population density of S. breviflora at different growth stages except in extremely wet and dry years. Our study suggests that under heavy grazing, S. breviflora uses an “opportunistic” ecological strategy to ensure population maintenance by increasing the seed germination rate and reducing dispersal via changes in associated seed phenotypic traits.