Abscisic acid regulates seed germination of Vellozia species in response to temperature

• The relationship between the phytohormones, gibberellin (GA) and abscisic acid (ABA) and light and temperature on seed germination is still not well understood. We aimed to investigate the role of the ABA and GA on seed germination of Vellozia caruncularis, V. intermedia and V. alutacea in response to light/dark conditions on different temperature.
• Seeds were incubated in GA (GA₃ or GA₄) or ABA and their respective biosynthesis inhibitors (paclobutrazol – PAC, and fluridone – FLU) solutions at two contrasting temperatures (25 and 40 °C). Furthermore, endogenous concentrations of active GAs and those of ABA were measured in seeds of V. intermedia and V. alutacea during imbibition/germination.
• Exogenous ABA inhibited the germination of Vellozia species under all conditions tested. GA, FLU and FLU + GA₃ stimulated germination in the dark at 25 °C (GA₄ being more effective than GA₃). PAC reduced seed germination in V. caruncularis and V. alutacea, but did not affect germination of V. intermedia at 40 °C either under light or dark conditions. During imbibition in the dark, levels of active GAs decreased in the seeds of V. intermedia, but were not altered in those of V. alutacea. Incubation at 40 °C decreased ABA levels during imbibition in both V. caruncularis and V. alutacea.
• We conclude that the seeds of Vellozia species studied here require light or high temperature to germinate and ABA has a major role in the regulation of Vellozia seed germination in response to light and temperature.

     

Allelopathic effects of the aqueous extract of Rhazya stricta on growth and metabolism of Salsola villosa

Abstract

Allelopathy is a biological process in which plants synthesize allelochemicals that affect the physiological properties, development and survival of other plants. Experiments were conducted to investigate the allelopathic effect of Rhazya stricta leaf extracts on the germination, early seedling growth and metabolism of Salsola villosa. Aqueous extracts (10, 30 and 50 g/ L) decreased germination and growth by reducing the synthesis of chlorophyll pigments. Leachate treatments induced the antioxidant system by upregulating antioxidant enzyme activities. Additionally, the activities of phenylalanine ammonia lyase and indole acetic acid oxidase were stimulated by exposure to leachate. R. stricta leachates reduced the content of polyunsaturated membrane fatty acids with a concomitant increase in the saturated ones. Unsaturated fatty acids were reduced with the increased concentration of leachate. Phospholipids were also reduced due to leachate, thereby affecting membrane functioning considerably. Aqueous extracts from the leaves of R. stricta restrict the growth and metabolism of S. villosa by hampering membrane functioning and photosynthetic capacity.     

Diversity of epicotyl dormancy among tropical montane forest species in Sri Lanka

• Fruiting season of many Sri Lankan tropical montane species is not synchronised and may not occur when conditions are favourable for seedling establishment. We hypothesised that species with different fruiting seasons have different seed dormancy mechanisms to synchronise timing of germination with a favourable season for establishment. Using six species with different fruiting seasons, we tested this hypothesis.
• Germination and imbibition of intact and manually scarified seeds were studied. Effect of GA₃ on germination was examined. Embryo length:seed length (E:S) ratio of freshly matured seeds and of those with a split seed coat was determined. Time taken for radicle and plumule emergence and morphological changes of the embryos were recorded.
• The radicle emerged from Ardisia missionis, Bheza nitidissima and Gaetnera walkeri seeds within 30 days, whereas it took >30 days in other species. Embryos grew in seeds of B. nitidissima and G. walkeri prior to radicle emergence but not in Microtropis wallichiana, Nothapodytes nimmoniana and Symplocos cochinchinensis. A considerable delay was observed between radicle and plumule emergence in all six species. Warm stratification and/or GA₃ promoted germination of all species.
• All the tested species have epicotyl dormancy. Seeds of B. nitidissima and G. walkeri have non‐deep simple morphophysiological epicotyl dormancy, and the other four species have non‐deep physiological epicotyl dormancy. Differences in radicle and epicotyl dormancy promote synchronisation of germination to a favourable time for seedling development. Therefore, information on dormancy‐breaking and germination requirements of both radicle and epicotyl are needed to determine the kind of dormancy of a particular species.

     

Comparison of Polyphenol Profile and Antimutagenic and Antioxidant Activities in Two Species Used as Source of Solidaginis herba – Goldenrod

European Pharmacopoeia accepts two equivalent species Solidago canadensis L. and S. gigantea Aiton as goldenrod (Solidaginis herba). We compared phytochemical profile of both species from invasive populations in Poland. Further, we compared in vitro antimutagenic and antioxidant activities of solvent extracts from aerial (AP) and underground parts (UP). In S. gigantea, flavonoid profile was dominated by quercetin glycosides, with quercitrin as the major compound. In S. canadensis, quercetin and kaempferol rutinosides were two major constituents. Caffeoylquinic acids (CQAs) were less diverse with 5‐CQA as a main compound. In UP, over 20 putative diterpenoids were detected, mostly unidentified. Several CQAs were present in higher amounts than in AP. Antioxidant and antimutagenic activities were different between species and organs, with the strongest inhibition of lipid peroxidation by Et₂O and AcOEt fractions from AP of both species (IC₅₀ 13.33 – 16.89 μg/mL) and BuOH fraction from S. gigantea UP (IC₅₀ = 13.32 μg/mL). Chemical mutagenesis was completely inhibited by non‐polar fractions, but oxidative mutagenesis was inhibited up to 35% only by S. canadensis. No clear relationship was found between chemical profiles and antimutagenic activity. In conclusion, both species have diverse activity and their phytochemical profiles should be considered in quality evaluation. UP of these weeds can also provide potential chemopreventive substances for further studies.     

Maintenance of photosynthesis and the antioxidant defence systems have key roles for survival of Halopeplis perfoliata (Amaranthaceae) in a saline environment

• Coastal salt marsh plants employ various combinations of morphological and physiological adaptations to survive under saline conditions. Little information is available on salinity tolerance mechanisms of Halopeplis perfoliata, a C3 stem succulent halophyte.
• We investigated the growth, photosynthesis and antioxidant defence mechanisms of H. perfoliata under saline conditions (0, 150, 300 and 600 mM NaCl) in an open greenhouse.
• Optimal shoot succulence, projected shoot area and relative growth rate were obtained in the low (150 mm NaCl) salinity treatment, while growth was inhibited at the highest salinity (600 mm NaCl). The CO₂ compensation point and carbon isotope composition of biomass confirmed C₃ photosynthesis. Increases in salinity did not affect the photosynthetic pigment content or maximum quantum efficiency of PSII of H. perfoliata. Assimilation of CO₂ (A) also remained unaffected by salinity. A modest effect on some gas exchange and photochemistry parameters was observed at 600 mm NaCl. With increasing salinity, there was a continual increase in respiration, suggesting utilisation of energy to cope with saline conditions. Under 300 and 600 mm NaCl, there was an increase in H₂O₂ and MDA with a concomitant rise in AsA, GR content and CAT activity.
• Hence, H. perfoliata appears to be an obligate halophyte that can grow up to seawater salinities by modulating photosynthetic gas exchange, photochemistry and the antioxidant defence systems.

     

Morphological and functional seed traits of the wild medicinal plant Dioscorea strydomiana,the most threatened yam in the world

• Morphological and functional seed traits have important roles in characterising the species regeneration niche and help to understand the reproductive biology of rare and threatened plants, which can thus support appropriate plant conservation measures.
• Seed morphometric and dispersal kinetics of the critically endangered Dioscorea strydomiana were measured and compared with those of four other Dioscorea species, and seed germination response under constant temperatures (5–35 °C) was compared with that of the congeneric and widespread D. sylvatica.
• Seed mass of D. strydomiana (ca. 14 mg) was twice that of D. sylvatica, but similar to or smaller than the other species examined. Seeds of D. strydomiana have the lowest speed of descent and lowest variability in most of the morphological traits considered, suggesting lower phenotypic plasticity but higher variance in the wing‐loading value. Seeds of D. strydomiana reached maximum germination at 15 °C (ca. 47%), which decreased slightly to ca. 37% at 25 °C and was completely inhibited at 35 °C. D. sylvatica seeds started to germinate at 10 °C (ca. 3%), reached 75–80% germination at 15–20 °C and maximum (ca. 90%) at 25–30 °C. Base temperatures for germination (T_b) were 9.3 and 5.7 °C, for D. strydomiana and D. sylvatica, respectively. Due to the higher germination percentages of D. sylvatica, ceiling and optimum temperatures could also be modelled for this species, suggesting higher sensitivity to high temperature for seeds of D. strydomiana.
• The detected poor seed lot quality of D. strydomiana suggests difficulties in reproduction from seed, highlighting the need for further investigation and conservation actions for this threatened yam species.

     

Comparison Study of Allelochemicals and Bispyribac-Sodium on the Germination and Growth Response of Echinochloa crus-galli L.

The phytotoxic effects of two allelochemicals (trans-cinnamic acid and syringaldehyde) at different concentrations (1000, 100, 10, and 1 µM) on seed germination, seedling growth, and physiological and biochemical changes of Echinochloa crus-galli L. were tested by comparison to a commercial herbicide ‘Nominee’ (that is, 100 g/L bispyribac-sodium). trans-Cinnamic acid and the herbicide inhibited seed germination completely at 100 µM, whereas for syringaldehyde, complete inhibition required 1000 µM. However, with 100 µM syringaldehyde, the seed germination of the test species was 53% of the control. Allelochemicals and the herbicide delayed seed germination and significantly affected the speed of germination index (S), speed of cumulative germination index (AS), and coefficient of germination rate (CRG). The roots were more affected when nutrients were not added to the growth bioassay. In general, with the increasing concentration of allelochemicals from 100 to 1000 µM, the inhibitory effects increased. Via microscopy analysis, we found leaf blade wilting and necrosis at concentrations above 100 µM in allelochemical-treated plants. Roots of E. crus-galli treated with 1000 µM allelochemicals had black points on root nodes but had no root hairs. The anatomy of roots treated with allelochemicals (1000 µM) showed contraction or reduction of root pith cells as well as fewer and larger vacuoles compared to the control. The allelochemicals also showed remarkable effects on seedling growth, SPAD index, chlorophyll content, and free proline content in a pot culture bioassay, indicating that trans-cinnamic acid and syringaldehyde are potent inhibitors of E. crus-galli growth and can be developed as herbicides for future weed management strategies.

     

Understanding biological and ecological factors affecting seed germination of the multipurpose tree Anogeissus leiocarpa

• Anogeissus leiocarpa (DC.) Guill. & Perr. (Combretaceae) has important economic and cultural value in West Africa as source of wood, dye and medicine. Although this tree is in high demand by local communities, its planting remains limited due to its very low propagation via seed.
• In this study, X‐rays were used to select filled fruits in order to characterise their morphology and seed germination responses to treatment with sulphuric acid and different incubation temperatures.
• Morphological observations highlighted a straight orthotropous seed structure. The increase in mass detected for both intact and scarified fruits through imbibition tests, as well as morphological observations of fruits soaked in methylene blue solution, confirmed that they are water‐permeable, although acid‐scarified fruits reached significantly higher mass increment values than intact ones. Acid scarification (10 min soaking in 98% H₂SO₄) positively affected seed germination rate but not final germination proportions. When intact fruits where incubated at a range of temperatures, no seeds germinated at 10 °C, while maximum seed germination (ca. 80%) was reached at 20 °C. T₅₀ values ranged from a minimum of ca. 12 days at 25 °C to a maximum of ca. 34 days at 15 and 35 °C. A theoretical base temperature for germination (T_b) of ca. 10 °C and a thermal requirement for 50% germination (S) of ca. 195 °Cd were also identified for intact fruits.
• The results of this study revealed the seed germination characteristics driven by fruit and seed morphology of this species, which will help in its wider propagation in plantations.

     

Morphological and chemical variation of Stemona tuberosa from southern China – Evidence for heterogeneity of this medicinal plant species

• The occurrence of bioactive alkaloids and tocopherols was studied in 15 different provenances of Stemona tuberosa Lour. collected in southern China, to examine chemical variation of individuals that show notable differences in flower characteristics. Morphological variations stimulated examination of chemical characteristics of these individuals.
• Methanolic root extracts of 15 individuals of S. tuberosa were comparatively assessed with HPLC‐UV‐DAD/ELSD. Five of seven compounds were co‐chromatographically identified. Two compounds were isolated and their structure elucidated using NMR and MS. Amounts of alkaloids and tocopherols were determined using HPLC‐UV‐DAD/ELSD with the external standard method.
• Five alkaloids, tuberostemonine ( 1 ), tuberostemonine A ( 2 ), neotuberostemonine ( 3 ), tuberostemonine N ( 4 ), stemoninine ( 5 ) and two 3,4‐dehydrotocopherol derivatives were identified. Within S. tuberosa alkaloid accumulation tends either towards tuberostemonine ( 1 ) or stemoninine ( 5 ). All individuals show a notable co‐occurrence of compounds 1 or 5 and 3,4‐dehydro‐δ‐tocopherol ( 6 ). These results coincide with differences in flower morphology of S. tuberosa.
• Stemona tuberosa, as defined in the Flora of China, shows a remarkable variation in flower morphology and additionally in the accumulation of alkaloids. The obtained data show the need for future species delimitation to either species or subspecies level.

     

Studies on lead and cadmium toxicity in Dianthus carthusianorum calamine ecotype cultivated in vitro

• Information on metallophytes during reclamation of land contaminated with heavy metals is sparse. We investigated the response of D. carthusianorum calamine ecotype to Pb and Cd stress. We focused on in vitro selection of tolerant plant material for direct use in chemically degraded areas.
• Shoot cultures were treated with various concentrations of Pb or Cd ions. Plantlet status was estimated as micropropagation efficiency, growth tolerance index (GTI) and through physiological analysis. Moreover, determination of plant Pb, Cd and other elements was performed.
• The application of Pb(NO₃)₂ resulted in stronger growth inhibition than application of CdCl₂. In the presence of Pb ions, a reduction was observed of both, the micropropagation coefficient to 1.1–1.8 and the GTI to 48%. In contrast, Cd ions had a positive influence on tested cultures, expressed as an increase of GTI up to 243% on medium enriched with 1.0 μm CdCl₂. Moreover, photosynthetic pigment content in shoots cultivated on media with CdCl₂ was higher than in control treatment. The adaptation to Cd was associated with decreased accumulation of phenols in the order: 0.0 μm  > 1.0 μm > 3.0 μm  > 5.5 μm CdCl₂. It seems that high tolerance to Cd is related to K uptake, which is involved in antioxidant defence.
• This work presents an innovative approach to the impact of Cd ions on plant growth and suggests a potential biological role of this metal in species from metalliferous areas.

     

Plant–soil feedbacks of forest understorey plants transplanted in nonlocal soils along a latitudinal gradient

• Climate change is driving movements of many plants beyond, as well as within, their current distributional ranges. Even migrant plants moving within their current range may experience different plant–soil feedbacks (PSF) because of divergent nonlocal biotic soil conditions. Yet, our understanding to what extent soil biotic conditions can affect the performance of within‐range migrant plants is still very limited.
• We assessed the emergence and growth of migrant forest herbs (Milium effusum and Stachys sylvatica) using soils and seeds collected along a 1,700 km latitudinal gradient across Europe. Soil biota were manipulated through four soil treatments, i.e. unsterilized control soil (PSF_US), sterilized soil (PSF_S), sterilized soil inoculated with unsterilized home soil (PSF_S+HI) and sterilized soil inoculated with unsterilized foreign soil (PSF_S+FI, expected to occur when both plants and soil biota track climate change).
• Compared to PSF_S, PSF_US had negative effects on the growth but not emergence of both species, while PSF_S+FI only affected S. sylvatica across all seed provenances. When considering seed origin, seedling emergence and growth responses to nonlocal soils depended on soil biotic conditions. Specifically, the home–away distance effect on seedling emergence differed between the four treatments, and significant responses to chemistry either disappeared (M. effusum) or changed (S. sylvatica) from PSF_US to PSF_S.
• Soil biota emerge as an important driver of the estimated plant migration success. Our results of the effects of soil microorganisms on plant establishment provide relevant information for predictions of the distribution and dynamics of plant species in a changing climate.

     

Effects of elevated CO2 on life‐history traits of three successive generations of Frankliniella occidentalis and F. intonsa on kidney bean,Phaseolus vulgaris

The objective of this study was to determine how elevated CO₂ impacts on life‐history traits and life table parameters in three successive generations of invasive species Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and its related native species, Frankliniella intonsa (Pergande), fed with kidney bean leaves grown in ambient CO₂. The oviposition period, sex ratio, net reproductive rate (R₀), intrinsic rate of increase (r_m), and finite rate of increase (λ) of F. occidentalis increased in elevated CO₂, and larval duration, survival rate, mean generation time (T), and population doubling time (DT) decreased. For F. intonsa, larval duration, survival rate, oviposition period, longevity of female adults, R₀, r_m, and λ decreased in elevated CO₂, whereas sex ratio, T, and DT increased. These results indicated that the effects of elevated CO₂ would be beneficial to F. occidentalis, whereas it would be detrimental to F. intonsa. However, the effects of elevated CO₂ on F. occidentalis and F. intonsa differed over generations. In elevated CO₂, larval duration, survival rate, oviposition period, sex ratio, r_m, and λ of F. occidentalis increased linearly through successive generations, whereas T and DT decreased linearly, which suggested that the effects of elevated CO₂ on F. occidentalis would be slowly accentuated over time. For F. intonsa, larval duration, survival rate, oviposition period, r_m, and λ decreased linearly over generations, whereas sex ratio, T, and DT increased linearly. This indicated that the effects of elevated CO₂ on F. intonsa would slowly accentuate over time. We conclude that F. occidentalis would be more adapted to elevated CO₂ than F. intonsa.     

Heteromorphic seeds of wheat wild relatives show germination niche differentiation

• Crop wild relatives are fundamental genetic resources for crop improvement. Wheat wild relatives often produce heteromorphic seeds that differ in morphological and physiological traits. Several Aegilops and Triticum species possess, within the same spikelet, a dimorphic seed pair, with one seed being larger than the other. A comprehensive analysis is needed to understand which traits are involved in seed dimorphism and if these aspects of variation in dimorphic pairs are functionally related.
• To this end, dispersal units of Triticum urartu and five Aegilops species were X‐rayed and the different seed morphs weighed. Germination tests were carried out on seeds, both dehulled and left in their dispersal units. Controlled ageing tests were performed to detect differences in seed longevity among seed morphs, and the antioxidant profile was assessed in terms of antioxidant compounds equipment and expression of selected antioxidant genes. We used PCA to group seed morphs sharing similar patterns of germination traits, longevity estimates and antioxidant profile.
• Different seed morphs differed significantly in terms of mass, final germination, germination timing, longevity estimates and antioxidant profile in most of the tested species. Small seeds germinated slower, had lower germination when left in their dispersal units, a higher antioxidant potential and were longer‐lived than large seeds. The antioxidant gene expression varied between morphs, with different patterns across species but not clearly reflecting the phenotypic observations.
• The results highlight different trait trade‐offs in dimorphic seeds of Aegilops and T. urartu, affecting their germination phenology and longevity, thereby resulting in recruitment niche differentiation.

     

Comparison of seed and seedling functional traits in native Helianthus species and the crop H. annuus (sunflower)

• Seed functional traits of native Helianthus species contribute towards ecosystem services but limitations to their use in managed programmes exist. Many perennial Helianthus possess seed dormancy. The ability for germination to occur under different temperature and drought conditions, as well as the capacity of germinated seeds to convert into normal seedlings is rarely considered. Our aim was to identify and quantify these constraints through functional trait analyses.
• In five seed lots of native Helianthus (four perennial and one annual) and five genotypes of sunflower (H. annuus) for comparison, dormancy, thermal and hydro thresholds and times, morphology, mass, oil content and conversion into normal seedlings were quantified. The influence of the seed collection site environment on these traits was also explored.
• Seed dormancy of the perennial species was overcome by scarification followed by germination in 5 mm GA₃. Thermal and hydro‐time analyses revealed slower germination for the native seed lots (>1350 °Ch) in comparison to the sunflower genotypes (<829.9 °Ch). However, native seed lots had a higher capacity to convert into normal seedlings at high temperatures and low water potentials than sunflower genotypes. For the native seed lots, the average monthly temperature of the collection site was negatively correlated with thermal time.
• Variability in seed functional traits of native Helianthus and greater capacity for germinated seeds to convert into normal seedlings suggests they are better equipped to cope with high temperature and drought scenarios than sunflower. Effective dormancy alleviation is required to facilitate the use of native Helianthus species.

     

Reproductive characteristics in an understory bamboo and gradual environmental changes after its dieback provide an extended opportunity for overstory tree regeneration in a mixed cool-temperate forest in central Japan

• The reproductive characteristics of understory bamboo and the effects of dieback on overstory tree seedlings through temporal changes in the environment at the forest floor have only been examined in a few bamboo species, due to the unpredictable occurrence of flowering events and long intervals between them but provide valuable information on tree regeneration and succession in a forest with dense dwarf bamboo cover.
• We investigated environmental conditions and assessed seedlings (< 30-cm tall) of the dwarf bamboo Sasa borealis and overstory tree species at 44–50 measurement points during 2016–2021, which included a S. borealis mass flowering event in 2017. We also conducted seed germination tests to determine germination rates and patterns in S. borealis. Environmental factors affecting seedling recruitment of S. borealis and of overstory trees were analysed using spatiotemporal generalized linear mixed models in the Bayesian framework.
• We observed gradual temporal changes in the environment, including increasing canopy openness and decreasing maximum height of dead S. borealis culms. The seeds germinated slowly and the emergence of current-year S. borealis seedlings peaked in spring–summer in 2019. The tree seedling density after 2019 increased significantly compared to that before the dieback. The model results suggest that tree seedling establishment was enhanced by increased light availability.
• Continuous field observation beginning before S. borealis dieback revealed gradually enhanced tree recruitment in response to slow decay of the remaining dead culms and slow recovery of S. borealis. The seedling regeneration pattern of understory bamboo partly contributes to a prolonged opportunity for overstory tree regeneration.

     

Allelopathic Effects of Castanea henryi Aqueous Extracts on the Growth and Physiology of Brassica pekinensis and Zea mays

The present study investigated the allelopathic effects of aqueous extracts of Castanea henryi litter on the growth and physiological responses of Brassica pekinensis and Zea mays. Treatment with high concentrations of leaf extract (0.05 g/ml for B. pekinensis and 0.10 g/ml for Z. mays) significantly increased malonaldehyde content and reduced seed germination, seedling growth, chlorophyll content, and the activity levels of antioxidant enzymes. These effects generally increased with increasing extract concentration. However, in Z. mays, low extract concentrations actually promoted seed germination, shoot growth, chlorophyll content, and antioxidant enzyme activity. The allelopathic effects of the various C. henryi extracts decreased as follows: leaf extract > twig extract > shell extract. Eleven potential allelochemicals including rutin, quercetin, luteolin, procyanidin A2, kaempferol, allantoin, propionic acid, salicylic acid, jasmonic acid, methylmalonic acid, and gentisic acid were identified in the leaves of C. henryi which were linked to the strongest allelopathic effects. These findings suggest that the allelopathic effects of C. henryi differ depending on receptor plant species, and that leaves are the most allelopathic litter in C. henryi.     

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.

     

Seed germination and dormancy traits of forbs and shrubs important for restoration of North American dryland ecosystems

• In degraded dryland systems, native plant community re‐establishment following disturbance is almost exclusively carried out using seeds, but these efforts commonly fail. Much of this failure can be attributed to the limited understanding of seed dormancy and germination traits.
• We undertook a systematic classification of seed dormancy of 26 species of annual and perennial forbs and shrubs that represent key, dominant genera used in restoration of the Great Basin ecosystem in the western United States. We examined germination across a wide thermal profile to depict species‐specific characteristics and assessed the potential of gibberellic acid (GA₃) and karrikinolide (KAR₁) to expand the thermal germination envelope of fresh seeds.
• Of the tested species, 81% produce seeds that are dormant at maturity. The largest proportion (62%) exhibited physiological (PD), followed by physical (PY, 8%), combinational (PY + PD, 8%) and morphophysiological (MPD, 4%) dormancy classes. The effects of chemical stimulants were temperature‐ and species‐mediated. In general, mean germination across the thermal profile was improved by GA₃ and KAR₁ for 11 and five species, respectively. We detected a strong germination response to temperature in freshly collected seeds of 20 species. Temperatures below 10 °C limited the germination of all except Agoseris heterophylla, suggesting that in their dormant state, the majority of these species are thermally restricted.
• Our findings demonstrate the utility of dormancy classification as a foundation for understanding the critical regenerative traits in these ecologically important species and highlight its importance in restoration planning.

     

Effect of maturation conditions on light and temperature requirements during seed germination of Citrullus colocynthis from the Arabian Desert

• Seed germination of Citrullus colocynthis, as in many other species of Cucurbitaceae, is inhibited by light, particularly at low temperatures. Germination response to light and temperature has been attributed to day length and temperature during seed maturation. This study assessed the effects of these factors on the germination response of C. colocynthis to temperature and light quality.
• Ripe fruits were collected from natural habitats during December and February and germinated at three temperatures (15/25, 20/30 and 25/35 °C) in five light treatments (dark, white light and Red:Far Red (R:FR) ratios of 0.30, 0.87 and 1.19). Additionally, unripe fruits were also collected from natural habitats and completed their maturation in growth chambers under different day lengths (6, 16 and 24 h of darkness) at 10/20 °C, and in darkness at both 10/20 °C and 25/35 °C. Mature seeds of the different treatments were germinated in the same five light treatments at 15/25 °C.
• Germination was significantly higher in the dark than that in any light treatment. Seeds matured at higher temperatures (i.e. seeds from the December collection and those matured at 25/35 °C) had significantly higher germination than those matured at lower temperatures (i.e. seeds from the February collection and those matured at 10/20 °C). Dark germination was significantly higher for the December collection than for the February collection. Seeds of the two collections germinated in the dark only at 15/25 °C. However, seeds matured in a growth chamber at 10/20 °C in darkness germinated at 15/25 °C in all light treatments, except for the R:FR ratio 0.30. Seeds of the different treatments failed to germinate in FR‐rich light.
• This study demonstrates that both temperature and day length during seed maturation play significant roles in the germination response of C. colocynthis. Additionally, the dark requirement for germination is likely beneficial for species with the larger seeds, such as C. colocynthis, which produce bigger seedlings that are able to emerge from deep soils and are competitively superior under dense vegetation and resource‐limited conditions.