Optimum Temperature For Germination Research Articles

Longevity and persistence of arrowleaf sida seeds in soil and emergence modeling using thermal and hydrothermal time models

Arrowleaf sida (Sida rhombifolia L.) is a weed that has a fibrous stem, aggressive root system and waxy leaves that can hinder herbicide absorption. Based on knowledge of the environmental requirements for germination of this species, it is possible to predict emergence to assist in integrated management. The aim of this investigation was to characterize the air temperature and soil water potential requirements for arrowleaf sida germination, to model the emergence in the field using thermal and hydrothermal time models and to evaluate the longevity of the arrowleaf sida seed bank. Laboratory experiments were conducted to determine the temperature and water potential for seed germination by testing eight temperatures (10, 15, 20, 25, 30, 35, 40, and 45 °C) and 10 water potentials (0, −0.05, −0.1, −0.2, −0.4, −0.6, −0.9, −1.2, −1.5, and −2.0 MPa). Field experiments were conducted between 2014 and 2018 to model the emergence using three sampling times (starting on 10/20, 11/10, and 12/01), during which soybean seeds were sown. To evaluate the longevity and persistence of the seed bank, a factorial experiment was conducted, in which the first factor included three burial depths (0, 3, and 6 cm) and the second factor included five collection times (0, 1, 4, 10, and 16 months) after seed burial. The base, optimal and maximum temperatures for arrowleaf sida germination were 10.0, 24.8, and 42.5 °C, respectively, and the base water potential was −1.20 MPa. It is possible to predict the emergence of arrowleaf sida in the field by hydrothermal and thermal time models under different environmental conditions. In addition, this species has a persistent seed bank, with 30% of seeds being viable after 16 months of burial.

The MKK3 MAPK cascade integrates temperature and after-ripening signals to modulate seed germination

The timing of seed germination is controlled by the combination of internal dormancy and external factors. Temperature is a major environmental factor for seed germination. The permissive temperature range for germination is narrow in dormant seeds and expands during after-ripening (AR) (dormancy release). Quantitative trait loci analyses of preharvest sprouting in cereals have revealed that MKK3, a mitogen-activated protein kinase (MAPK) cascade protein, is a negative regulator of grain dormancy. Here, we show that the MAPKKK19/20-MKK3-MPK1/2/7/14 cascade modulates the germination temperature range in Arabidopsis seeds by elevating the germinability of the seeds at sub- and supraoptimal temperatures. The expression of MAPKKK19 and MAPKKK20 is induced around optimal temperature for germination in after-ripened seeds but repressed in dormant seeds. MPK7 activation depends on the expression levels of MAPKKK19/20, with expression occurring under conditions permissive for germination. Abscisic acid (ABA) and gibberellin (GA) are two major phytohormones which are involved in germination control. Activation of the MKK3 cascade represses ABA biosynthesis enzyme gene expression and induces expression of ABA catabolic enzyme and GA biosynthesis enzyme genes, resulting in expansion of the germinable temperature range. Our data demonstrate that the MKK3 cascade integrates temperature and AR signals to phytohormone metabolism and seed germination.

Hot and fast: seed ecology for restoration relevant species in the Argyle region of the east Kimberley, Australia

This study investigates the germination requirements of 12 plant species native to the Argyle region of the east Kimberley, a biodiverse monsoonal tropical region characterized by high temperatures, high evaporation, and episodic seasonal rainfall. The research involved quality assessment of mature seeds, followed by dormancy alleviation and laboratory‐based germination to determine the responses of seeds to a range of temperatures (5–40°C) in terms of germination speed (T10), mean germination time, and maximum germination proportion. Data were then modeled to calculate the optimal temperature to support germination for each species. The results showed that germination rapidly commences in response to a wide range of temperatures typical of the wet season (November–February) in the east Kimberley, though germination for most species was still high (>50%) after exposure to temperatures as low as 15°C. Mean optimal temperature for germination across all species was 25.8 ± 1.5°C, with minimal variation between most species, the exception being Dodonaea physocarpa, which preferred cooler temperatures (Topt = 14.0°C). The speed of germination was also rapid (T10 = 1–3 days) across all species at the optimal germination temperature. The findings suggest that temperature is not a limiting factor for germination in this region and that the onset and intensity of the wet season are the most significant factors determining successful germination, emergence, and seedling establishment. The study underscores the importance of species‐specific understanding of environmental temperatures required for seed germination in seed‐based restoration efforts and informs the planning of direct seeding works, thus enhancing restoration outcomes.

Response of spiny cocklebur (Xanthium spinosum) and common cocklebur (X. strumarium) seed germination to environmental and soil factors

Context Seed germination and seedling emergence are affected by many environmental factors. Knowledge regarding factors affecting seed germination of spiny cocklebur (Xanthium spinosum L.) and common cocklebur (X. strumarium L.) could help determine their potential distribution and control strategies. Aims The present study was conducted to investigate the effect of key environmental factors on seed germination and seedling emergence of spiny cocklebur and common cocklebur. Methods Seed germination of spiny cocklebur and common cocklebur was tested at various constant and alternating temperatures, pH, salinity and moisture stress. The effect of flooding height, burial depth and soil type on seedling emergence was also investigated. Key results The optimum constant temperature for germination of spiny cocklebur was 25°C, and 35°C and higher for common cocklebur. Under alternating temperature, maximal germination was at 25/15°C and 35/15°C for spiny cocklebur and common cocklebur, respectively. Maximum germination of both spiny cocklebur and common cocklebur was at neutral pH. Spiny cocklebur germination was not suppressed as much by lower and higher pH or by an increasing salinity as was common cocklebur germination. Conclusions Common cocklebur appears to be better adapted to warmer environments than is spiny cocklebur, but less so to a broad range of soil pH and salinity stress. Implications The different germination responses of common cocklebur and spiny cocklebur to the environmental factors of temperature, pH and salinity imply that the two species may occupy different niches across the landscape. Our knowledge of these responses can help in identifying potential areas for invasion for increased monitoring and management.

Determination of germination characteristics and salinity and drought tolerances of Mountain Swan (Atriplex nitens Schkuhr)

In this study, it was aimed to determine the appropriate seed germination temperature, salt tolerance, salinity and drought tolerance of seedlings in Mountain swan (Atriplex nitens). For this purpose, an experiment was established in 2021 in laboratory conditions according to the factorial experiment design in random plots and in greenhouse conditions according to the random plots experiment design with three replications. Firstly, 4 constant (10, 15, 20, 25, 30°C) and 2 variable (20/15, 25/15°C) temperatures were used in the refrigerated incubator. Total germination rates and average germination times of seeds with and without pericarp were determined. Secondly, 6 different salt concentrations (0, 100, 200, 300, 400 and 500 mM NaCl) were studied considering the optimum germination temperatures (25°C and 20/15°C). At the end of the study, germination rates (%), average germination times (days) and sensitivity indices (SI) were determined. In the last two stages, seedlings were subjected to 4 different salinity (0, 100, 200, 300, 400 and 500 mM NaCl) and 5 different drought (control, low, moderate, high and severe) tests under greenhouse conditions. At this stage, plant and root length, stem thickness, leaf area index (LAI), plant and root dry weight, root/plant ratio and tolerance percentage values were measured. As a result of the laboratory study, it was determined that seeds without pericarp had a better germination percentage than seeds with pericarp. The highest total and normal germination rates were obtained from 200 mM NaCl treatment at 20/15°C. Germination rate was determined from 0, 100 and 200 mM salt treatments at 25°C. These results showed that Atriplex nitens seeds could germinate in high salt concentrations and that their seedlings had high tolerance to drought and salinity.

Germination Kinetics of Ferula communis L. Seeds, a Potentially Multipurpose-Use Wild Species

Despite exhibiting intriguing features associated with its multipurpose applications and drought tolerance, Ferula communis remains a wild and uncultivated species, with limited experimental research on its biology, starting from seed germination and extending to its ecology. The purpose of this study was to investigate potential germination and kinetics in F. communis seeds in response to four cold stratification periods (0, 15, 45, and 90 days at a constant temperature of 5 °C) and four temperatures (5, 10, 15, and 20 °C) under continuous darkness. F. communis exhibited a pronounced germination potential exceeding 90%, with the optimal temperature for germination falling within the range of 5 °C to 15 °C, without necessitating cold stratification. A dramatic drop of the germination percentage was observed at 20 °C (<10%), suggesting a form of conditional dormancy attributed to the higher temperature tested.

Factors affecting the germination of teliospores of Sporisorium scitamineum and the development of sugarcane smut in the field

AbstractTemperature and water potential are critical factors influencing the germination of Sporisorium scitamineum teliospores and subsequent crop infection. This paper reports on the effect of temperature, water potential and incubation time on S. scitamineum teliospore germination. A field trial was conducted to determine the influence of temperature and length of exposure to teliospores on smut incidence. A 200 μL aliquot of teliospore (1.5 × 106 teliospores/mL) was cultured on water agar (WA) amended by potassium chloride (KCl) or sucrose. The plates were incubated across a range of temperatures and incubation times. For the field trial, sugarcane setts were inoculated and incubated at different temperatures and for varying incubation periods. The results demonstrated that germination decreased with declining water potential with either KCl or sucrose. The greatest germination (95.8%) occurred on unamended WA incubated at 30°C for 6 h. Even at the lowest water potential of −45 bars and 30°C, 50% teliospores were still able to germinate. These results indicate that 30°C is the optimum temperature for teliospore germination and that S. scitamineum may still germinate in fairly dry conditions. However, high temperatures (40°C), greatly reduce S. scitamineum germination. These results are consistent with field trial outcomes, which showed that the highest disease incidence (40.4%) occurred when temperature of inoculation was maintained at 30°C. On the other hand, the incidence was significantly reduced to 5.7% at 35°C. The results suggested consistent conditions for teliospore germination and sugarcane bud infection, with a temperature of 30°C being optimal for both.

Intra‐specific variation and climate differentially shape the thermal germination niches of three co‐occurring woodland forbs

AbstractUnderstanding plant responses to temperature is critical for predicting their vulnerability to global warming and for planning management responses. Germination is a key life‐stage, strongly regulated by temperature, that affects the potential for plant populations to persist. Here, we compared the thermal germination niches of three unrelated, declining woodland forb species – Arthropodium fimbriatum (Asparagaceae), Bulbine bulbosa (Asphodelaceae), Microseris walteri (Asteraceae) – across common temperature and precipitation gradients, to characterize the relationships with home‐site climate, and associated implications for ecological restoration in a changing climate. Open‐pollinated seed were sampled from 14–15 populations per species across an aridity gradient in south‐eastern Australia. Germination responses for each population were tested in controlled temperature cabinets under five temperature regimes encompassing contemporary and projected future temperatures. Optimum germination temperature and thermal germination niche were characterized and assessed for associations with home‐site climate and potential germination under projected climate change. The three species showed significant intra‐specific variation in the thermal germination niche. Optimum germination temperature was correlated with home‐site climate, suggesting adaptive variation among populations in germination requirements. However, the pattern of variation in optimum germination across the environmental gradients was not always consistent among the species. Future temperatures projected under climate change tended to be outside the current thermal germination niche for all species, indicating potential benefits of incorporating pre‐adapted populations in ecological restoration. Climate‐related intra‐specific variation in the thermal germination niche provides evidence for local adaptation to climate in all three forb species and suggests potential differences among populations in vulnerability to global warming. These results emphasize the importance of understanding the extent of intra‐specific variation in key life history traits to better manage and conserve populations and restore their ecosystems as climates change.

Thermal optima for seed germination of 30 tree species from Central Amazonia: a comparison of approaches and a new proposal

This study compared the seed germination of 30 tree species from Central Amazonia using a wide temperature range (5-40°C with 12 hours of light daily). Seeds were submitted to pre-germination treatments, whenever necessary, sown on vermiculite or germitest paper, and normal seedling development was assessed until stabilisation. With the same data set, seeds' optimal germination temperature (Topt ) was determined by comparing the following approaches: (i) 2-step, the temperature with the highest germination and the shortest time to seed population reach 50% of germination was chosen; (ii) the highest Germination Speed Index (GSI); (iii) using the formula developed by Olff and collaborators (Olff's approach); (iv) three species were evaluated with Covell's approach; and (v) new formulas for Topt calculation are proposed, based on germination success and five different variables of germination rate (Cipriani's approach). Comparing the results, Topt differed between 0.6-10.0°C. GSI and 2-step indicated generally higher values than Olff's formula. The minimum and maximum Topt differences between Cipriani's approaches were between 0.1-2.2°C. Our study showed that Toptshould be determined for each species as, even the 30 Amazonian tree species of the same habitat, Topt ranged between 22.5 and 32.5°C.

Effects of Temperature on Spore Germination and Mycelial Growth of Calosphaeria pulchella, Cytospora sorbicola, and Eutypa lata Isolates Associated with Sweet Cherry Canker Diseases.

Although fungal canker diseases constitute a limiting factor to orchard productivity and longevity, little is known about the effects of temperature on spore germination and mycelial growth of the fungal causal agents. Accordingly, the germination of spores and colony growth of Calosphaeria pulchella, Cytospora sorbicola, and Eutypa lata were evaluated after incubation on 2% water agar and 4% potato dextrose agar, respectively, at 5, 10, 15, 20, 25, 30, 35, and 40°C. Temperature optima for spore germination and mycelial growth were derived from nonlinear models fitted to germination rates and colony diameter data. The optimal temperatures for spore germination of Cal. pulchella were 28.5°C for ascospores and 29.2°C for conidia. The optimal temperatures for Cyt. sorbicola conidia and E. lata ascospore germination were 25.8 and 23.1°C, respectively. The germination of ascospores and conidia of Cal. pulchella at temperatures below 15°C required an incubation time of at least 72 h. Ascospores of E. lata and conidia of Cyt. sorbicola germinated at 10°C after 36 h. The optimal temperature for colony growth of Cal. pulchella was 24.6°C, whereas it was 21.7°C for both Cyt. sorbicola and E. lata. Our study indicates that temperature requirements for basic biological functions are higher for Cal. pulchella than for Cyt. sorbicola and E. lata. The overall higher temperatures of California relative to other cherry-producing regions in the United States or worldwide could explain the prevalence of Calosphaeria canker in the state. Conversely, Cyt. sorbicola and E. lata appear better adapted to cooler temperatures.

Seed Priming Improves Enzymatic and Biochemical Performances of Rice During Seed Germination under Low and High Temperatures

As an abiotic stress, adverse germination temperatures cause serious disruptions in physiological and biochemical processes involved in seed germination. Using a factorial experiment, we examined the effects of different seed priming treatments on enzymatic and biochemical performances of rice seed germination under different temperatures. Each of the rice genotypes (Hashemi, Sadry-domsefid, IRON-70-7053-7 and NORIN-22) was primed with hydro-hardening, KCl, CaCl2 and ascorbic acid (AsA) and without a priming agent as a control at low (15 ºC), optimum (25 ºC) and high (35 ºC) germination temperatures. The results showed that the enzymatic and biochemical performances of all the rice genotypes were affected by the seed priming agents, especially under the low germination temperature. At 15 ºC, seed priming with AsA was found to be the best agent for the activities of amylase, α-amylase, catalase (CAT), peroxidase (POX), ascorbate peroxidase (APOX) and superoxide dismutase (SOD) as well as the content of soluble sugars in the NORIN-22 genotype, and for protease activity and soluble protein content in the IRON-70-7053-7 genotype. SOD at the low germination temperature and CAT, POX and protease at the optimum and high germination temperatures were the most important enzymes in occurrence of germination potential in terms of seedling length, vigor index, normal seedling rate and germination rate. Under the priming agents, the highest changes in normal seedling rate were observed at the low and optimum germination temperatures by AsA priming in the Hashemi and NORIN-22 genotypes, and at the high germination temperature under KCl priming in the Hashemi genotype.

Germination Ecology of African Lovegrass (Eragrostis curvula) and Herbicide Options for Its Control

African lovegrass (Eragrostis curvula) is one of the invasive perennial grasses that continues to disturb natural ecosystems globally. Experiments were conducted in southeast Queensland, Australia, to evaluate the effects of temperature, salt stress, water stress, burial depth, and sorghum crop residue load on the emergence and efficacy of postemergence herbicides on two populations (Clifton and Crows Nest) of E. curvula. The optimal germination temperature regimes for E. curvula were 30/20 and 35/25 °C, but seeds did not germinate at temperatures commonly occurring in the Queensland winter (15/5 °C). Total darkness inhibited germination by 79%, indicating that the shade cover effect would reduce germination of E. curvula. The Clifton population tolerated a higher concentration of sodium chloride (160 mM) and osmotic potential (−0.8 MPa). Under both salt and water stress, germination was 31% and 20% greater in the Clifton population than in Crows Nest, respectively, suggesting that the Clifton population is more tolerant to salt and drought stress. The maximum germination was obtained for the surface seeds while emergence declined with increased burial depth up to 4 cm. No seedlings emerged from the 8 cm depth. The addition of sorghum residue amounts up to 8 Mg ha−1 to the soil surface inhibited emergence compared to the no-residue treatment, suggesting that retention of heavy cereal residue will further delay or restrict emergence. Several postemergence herbicides were found to be effective in controlling E. curvula at an early stage. Information from this study will further compliment earlier studies on the targeted management of E. curvula populations.

Germination of the exotic Calotropis procera (Aiton) W.T. (Apocynaceae) in Mexico

Background: Seed germination strategies are important for exotic species to identify the factors that control seed germination and establishment.
 Questions and /or Hypotheses: Temperature and light germination requirements for seeds of Calotropis procera do not change neither in its native regions nor in lands where it is exotic. Calotropis procera show germination traits that may increase their probability of colonization.
 Studied species: Calotropis procera is a perennial plant native to some desertic areas in Asia and Africa and now naturalized in America.
 Study site and dates: Mature fruits were collected in Oaxaca in September 2019 to test germination parameters. The last experiment was conducted in September 2021.
 Methods: We determined the effect of different temperatures, photoblastic response, and loss of viability of seeds kept at laboratory conditions for two years. We performed several sowings under controlled conditions and achieved germinability, t50 and the time to germinate.
 Results: Seeds were non-dormant, neutral photoblastic and did not lose viability after two years of dry storage. Temperature affected germinability and t50. Optimum germination temperature was 30 °C with no germination above 40 °C.
 Conclusions: Germination requirements of seeds of Calotropis procera studied were similar to those reported worldwide. Though seed germination was affected by maximum mean temperatures, seeds germinated fast and at high percentages under a wide range of temperatures, which together with other attributes, may confer C. procera great chances for successful colonization.

Germination ecology and response to herbicides of Ludwigia prostrata and their implication for weed control in paddy fields

AbstractProstrate water primrose is a troublesome weed in rice paddy fields. A study was conducted to determine the influence of environmental and agronomic factors on its emergence. The efficacy of herbicides on this species was also examined. The germination percentage of mature seeds remained above 90% within 180 d after harvest, indicating a low primary dormancy of this species. Light stimulated seed germination. Seeds buried deeper than 0.5 cm did not form seedlings. These results suggest that stale seedbed practices and deep tillage operations can mitigate the occurrence of this species in paddy fields. The optimum temperature for germination varied from 25/15 C to 35/25 C. The osmotic potential and salt concentration needed to inhibit 50% of maximum germination were −0.4 MPa and 197 mM, respectively. Seeds were tolerant to flooding and did not germinate at pH 8 to 10. The preemergence herbicides oxadiazon, oxadiargyl, and butachlor had excellent control efficacy on prostrate water primrose, with a 95.4% to 100% reduction in seedling number and a 99.2% to 100% reduction in biomass, respectively. The postemergence herbicides MCPA-Na + bentazone, bentazone, MCPA-Na, and fluroxypyr applied at the 2- to 3-leaf stage of prostrate water primrose provided a 90.6% to 100% reduction in seedling number and a 99.3% to 100% reduction in biomass. The results of this study can help in developing sustainable and effective integrated weed management strategies for controlling prostrate water primrose in paddy fields.

The influence of temperature and vapour pressure deficit on conidia germination and germ tube production in an Australian Podosphaera xanthii isolate

Powdery mildew of cucurbits, caused by Podosphaera xanthii, is an economic constraint in cucurbit production worldwide. This study examined the influence of temperature and vapour pressure deficit (VPD) on the rate of conidial germination and the formation of germ tubes in an Australian P. xanthii isolate 12 – 48 h after inoculation. Two experiments were prepared by inoculating cucumber, cv. crystal salad, leaf-discs using a spore settling tower. The first experiment incubated inoculated cucumber leaf-discs at eight temperatures between 8 and 35 °C under saturated vapour pressure (SVP), the second compared 18 VPD conditions between 0.038 and 1.797 kPa, in six humidity chambers (33% – 99% relative humidity) and three temperatures (22 °C, 25 °C, 28 °C). Leaf-discs were cleared, stained and microscopically inspected for conidial germination and the number of germ tubes. The optimal temperature for germination was 28ºC at SVP, where more than 50% of conidia had germinated by 12 h, and 85% by 48 h. Fewer germinated conidia were recorded after 12 h at other temperature treatments between 17 °C and 31 °C. The germination percentage and germination rate were significantly lower when vapour pressure was between 0.13 and 2.5 kPa, with germination in response to VPD varying by approximately 10%, indicating difficulty associating conidial germination to VPD above 0.13 kPa. Germ tube production was highest between 25 ºC and 28 ºC at the lowest VPD treatment at near SVP, with more than 50% of the germinated conidia producing at least three germ tubes. Germination and formation of germ tubes significantly reduced when VPD increased. P. xanthii conidia were able to produce a primary germ tube under relatively dry conditions, such as 2.53 kPa, but these results show infection would be less likely and require longer incubation. This study provides the first crucial step in simulating powdery mildew infections on cucurbit plants and may lead to a model capable of providing risk forecasts or fungicide management decision support tools.

Germination and Seedling Development Responses of Sunflower (Helianthus annuus L.) Seeds to Temperature and Different Levels of Water Availability

Abiotic variables are crucial for seed germination and seedling development. In the present work, we attempted to determine the optimal conditions (temperature, water, seed density, and fungal growth) for sunflower seed development (Helianthus annus L. Larissza). The germination of sunflower seeds was investigated under controlled conditions at eight consistent temperatures: 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, and 40 °C. For the water test, there were 12 water levels based on one-milliliter intervals and 18 water levels based on thousand kernel weight (TKW). In addition, four seed densities (6, 8, 10, and 12) and two antifungal application techniques (sterilization and growing medium) were examined. The results showed that temperature has a significant effect on seed germination, germination timing, and seedling development. Temperatures between 15 and 35 degrees Celsius were optimal for germination, with 25 degrees Celsius being the optimal temperature for significant germination and seedling development. Beginning at 0.6 mL, or 125% of the TKW, sunflower seeds can germinate under a wide range of water availability. The optimal range for seedling development (8.2–11.4) is wider than the optimal range for dry matter accumulation, which is 5.8–8.2 mL or 1000–1625% of the TKW. The finding that a density of 10 to 12 seeds per 9 cm Petri dish demonstrates the most exceptional values is advantageous for future research and breeding projects, particularly when seeds are scarce. Seed priming is a more effective antifungal application technique than other techniques.

Modeling the influence of temperature, salt and osmotic stresses on seed germination and survival capacity of Stipa tenacissima L.

This work stands for a modelling approach to identify the cardinal temperature of germination of Stipa tenacissima L., its capacity to recover and its adaptation potential considering dormancy and viability after exposure to salinity and drought. Seed traits characterised before germination were tested. The seeds were incubated at temperatures of 10 to 30 °C and low osmotic potentials were induced using sodium chloride (NaCl) or polyethylene glycol (PEG 6000) solutions of 0 to −1.6 MPa. The capacity of seeds to recover and remain viable under stress conditions was quantified. Our results proved that the seed yields and sizes were uniform. The analysis of cardinal temperature by thermal time model exhibited an optimal germination temperature (T o) of about 19 °C, a base temperature (T b) of 0.6 °C and a ceiling temperature (T c) of 31 °C at 0 MPa. The base water potential Ψb (50) values ranged between −0.83 and −1.54 MPa and between −0.97 and −2.27 MPa for osmotic and salt stresses, at 30 °C and 20 °C, respectively. In conclusion, the species showed a lower seed recruitment related to a low drought tolerance (drought tolerance index = −0.5 MPa), To requirement and threshold sensitivity. Under salt stress, S. tenacissima used osmotic adjustment in order to germinate in a lower osmotic potential.

Recruitment of Melaleuca quinquenervia (Myrtaceae) in the fringing forests of the Myall Lakes, NSW, Australia

Context Melaleuca quinquenervia is a widespread, keystone species of eastern Australian coastal forested wetlands. Populations of M. quinquenervia in the fringes of Myall Lakes, New South Wales, Australia exhibit low numbers of juveniles, infrequent recruitment and a dominance of mature individuals, raising concerns about stand replacement from conservation managers. In contrast, M. quinquenervia often recruits in large numbers and is highly invasive in wetlands around the world. Aims To explore factors that limit recruitment of M. quinquenervia within its native range. Methods Field deployed seed traps; soil-core sampling; a burial longevity trial and depth of emergence experiment; laboratory temperature, salinity and light germination experiments; a transplantation experiment; monitoring of field germination; and a litter/leachate experiment. Key results Low seed viability (5–26%) is offset by high canopy seed loads (250 000 to 120 million seeds per tree) released continuously throughout the year with a peak fall in summer (2000 to 5000 viable seeds per m2 per month), coinciding with optimal germination temperatures. Seedling emergence is reduced below 5 mm soil depth, there is a very low soil seedbank reserve, and germination is light-dependant. M. quinquenervia exhibited reduced germination percentage and rate as well as reduced survival of seedlings at salinities higher than 15 dS m−1 EC (electrical conductivity). The most favourable sites for seedling establishment are permanently moist with low salinity, protected from wave action via sedge vegetation, and sheltered from prevailing winds. There is an inhibitory effect of Casuarina leachate on germination. Conclusions Germination in the field is episodic, and tied to specific environmental conditions. Highest losses occur at the seedling establishment phase. Implications Future research avenues and management recommendations are provided.

Climate and seed size of a dry forest species: influence on seed production, physiological quality, and tolerance to abiotic stresses

Abstract: Seed production, quality and germination are likely to be affected by a drastic climate change in semi-arid areas predicted for the end of the century. We evaluated Anadenanthera colubrina var. cebil (Griseb.) Altschu (Fabaceae) seeds of different sizes, populations and harvest years for germination and tolerance to environmental stresses aiming to predict impacts of future climate. Seeds were accessed for germination temperature, salinity and osmotic limits and requirements. Germination of large and small seeds harvested in different populations was evaluated in optimum and stressful temperature, salinity and water deficit. A glasshouse pot assay tested weekly irrigation regimes and seedlings emergence and growth. Optimal temperature for seeds germination was 34.8 oC and limits were 5.6 oC and 50.9 oC. Large and small-sized seeds do not differ in germination, however small seeds are more efficient in stressful conditions. Seedlings can emerge and grow under small weekly irrigation for four months. The predicted increase in temperature will not impair germination, however, the time available for seedling establishment will decrease due to lacking rainfall. The increase in the amount of small-sized seeds produced in drought years is a strategy for coping with harsh environments, rather than a decrease in seed quality.

Dormancy and germination characteristics of Tarenaya hassleriana (Cleomaceae) seeds

Abstract: Elucidating the physiological and ecological mechanisms of seed dormancy and germination is of great significance for species conservation and the application of plant resources. Based on Baskin and Baskin’s classification system for seed dormancy, the cause of dormancy in Tarenaya hassleriana (Cleomaceae) seeds was studied using alternating temperature, cold moist stratification, dry storage, and GA3 soaking treatment. The results indicated that fresh mature T. hassleriana seeds had a combinational dormancy, including a physical dormancy and a type 2 non-deep physiological dormancy, and were photoblastic, with an optimal germination temperature of 35°C. In addition, fresh mature T. hassleriana seeds may be efficiently released from dormancy and promoted to germinate by an alternating temperature of 20 °C/30 °C, cold moist stratification, and cold moist stratification following dry storage. Furthermore, GA3 soaking treatment could also promote dormancy release and subsequent germination at 35 °C, and dry storage treatment could promote dormancy release and subsequent germination at 5-15 °C. These results also suggested that there were complex cross-talks among phytohormone, osmotic potential, and the temperature signaling regulatory pathways during dormancy release and germination of T. hassleriana seeds, which deserve further study.