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Introduction: Plant seeds from weeds and energy crops have the potential to survive anaerobic digestion (AD). Species able to form physically dormant, i.e., hardseeded (HS) seeds seem particularly resistant. However, it is not yet known to what extent the storage of the digestate after AD affects seed viability. Methods: Seed survival of five HS and six non-HS (NHS) species was investigated in three combinations of digestate storage (DS) and AD. First, untreated seeds were exposed to DS for maximum 12 weeks. To simulate short-circuited AD (ADshort) in biogas reactors, seeds were second subjected to lab-scale AD for 1 day before DS. Third, seeds of six species were exposed to full-scale AD (ADfull) followed by DS. Seed viability was determined using a combination of germination tests and tetrazolium staining. Viability was modeled as a function of exposure time. Results and discussion: Seed viability was affected by DS, AD and AD + DS, but responses varied greatly between species and treatments. With increasing exposure time, viability decreased after a lag-phase, remained stable or even increased. The NHS species Cichorium intybus , Daucus carota , Echium vulgare , and Verbascum thapsus were most susceptible, with seed-killing close to 100% if DS was involved. The HS species Malva sylvestris , Melilotus albus and Melilotus officinalis were most resistant. They survived all treatments and were alive after 35 days of ADfull plus 3 months of DS. The resistance potential of the HS species Abutilon theophrasti and Malva alcea and of the NHS species Chenopodium album and two tomato varieties was intermediate. None of them survived ADfull + DS, but except A. theophrasti they were viable after ADshort + DS. With few exceptions, seed-killing by AD + DS was higher than that by AD alone. In conclusion, DS and AD + DS have the potential to reduce seed viability, but do not completely inactivate all species. Therefore, digestate can be contaminated with viable seeds and may lead to the spread of weeds, especially after a short-circuited AD. In order to ensure the sustainable use of digestates in terms of weeds, we recommend to investigate the factors contributing to seed inactivation and the quantity of seed introduced to AD. [ABSTRACT FROM AUTHOR]

The plant species Sesbania tomentosa (‘ōhai; Fabaceae) is endemic to the Hawaiian Islands, federally listed as endangered in the USA and has been proposed for categorization as Vulnerable on the IUCN Red List. In 2021, c. 12,000 seeds from 12 seed lots collected during 1990–1992 from across the Hawaiian Islands were discovered in ambient herbarium conditions (55% relative humidity (RH) at 20 °C). International gene bank standards suggest drying seeds in equilibrium with 15% RH and stored at −18 °C. To investigate seed viability, we mechanically scarified then sowed 15 seeds from each accession at daily alternating regimes of 12 h light and 12 h dark at temperatures of 25/15 °C, respectively. Germination was observed after 7 days and ended after 34 days. Mean final germination was 88.9 ± SD 0.1% (range 73–100%). Each seed lot was accessioned into the National Tropical Botanical Garden's Seed Bank and Laboratory. In seeds with a water-impermeable seed coat (i.e. physical dormancy), such as S. tomentosa, seeds can desorb but not absorb water. Therefore, if the seeds were initially dried, although exposed to high RH for up to 32 years, seed equilibrium RH may have remained low, which may in part explain the observed high germinability. This study holds significance for managers who are working to conserve this endangered Hawaiian species and suggests that even suboptimal conditions may still yield highly viable seeds several decades into the future.

The plant species Sesbania tomentosa ('ōhai; Fabaceae) is endemic to the Hawaiian Islands, federally listed as endangered in the USA and has been proposed for categorization as Vulnerable on the IUCN Red List. In 2021, c. 12,000 seeds from 12 seed lots collected during 1990–1992 from across the Hawaiian Islands were discovered in ambient herbarium conditions (55% relative humidity (RH) at 20 °C). International gene bank standards suggest drying seeds in equilibrium with 15% RH and stored at −18 °C. To investigate seed viability, we mechanically scarified then sowed 15 seeds from each accession at daily alternating regimes of 12 h light and 12 h dark at temperatures of 25/15 °C, respectively. Germination was observed after 7 days and ended after 34 days. Mean final germination was 88.9 ± SD 0.1% (range 73–100%). Each seed lot was accessioned into the National Tropical Botanical Garden's Seed Bank and Laboratory. In seeds with a water-impermeable seed coat (i.e. physical dormancy), such as S. tomentosa , seeds can desorb but not absorb water. Therefore, if the seeds were initially dried, although exposed to high RH for up to 32 years, seed equilibrium RH may have remained low, which may in part explain the observed high germinability. This study holds significance for managers who are working to conserve this endangered Hawaiian species and suggests that even suboptimal conditions may still yield highly viable seeds several decades into the future. [ABSTRACT FROM AUTHOR]

In a recent paper in Southern Forests , Jaganathan and co-workers indicated that the low constant-temperature drying method (LCTDM) (103°C for 17 h) is satisfactory for determining moisture content (MC) in seeds with physical dormancy (PY). Would this recommendation apply to Acacia , a large genus (1000+ species) with a seed coat so strong that seeds in the soil can maintain high viability for many decades? MC was assessed, using the LCTDM, in six Australian Acacia species by comparing intact seeds with those cut in half. Halved seeds of all species lost moisture rapidly and their mass had largely stabilised after about 2–3 h. Intact seeds had a wide variation in moisture-loss patterns. In some species, the testa was morphologically unchanged after 24 h at 103°C and this was associated with a relatively slow moisture loss. In other species, the testa had completely shattered after 8 h, leading to a rapid moisture loss. If the LCTDM is used to determine MC in Acacia species, it is advisable to employ a technique that substantially disrupts the testa. Moisture content (MC) is an important property of seeds, associated with many aspects of physiological seed quality. Acacias have very hard seed coats, which means that seeds can survive for decades in the soil, but in standard methods of determining MC (e.g. heating in an oven at 103°C for 17 h), the moisture in the seed might not be able to escape. The standard method can work for some Acacia species; however, to ensure accurate results, seeds should be halved before going into the oven. Image by Geoff Burrows. [ABSTRACT FROM AUTHOR]

ABSTRACT: Cycas revoluta seeds exhibit both physical and morphological dormancy, posing significant challenges to their germination. This study investigated the morphological characteristics and dormancy mechanisms of C. revoluta seeds and evaluated methods to overcome these dormancies. Seeds were harvested over two consecutive years and subjected to different treatments. A morphological analysis of seed structure was conducted, along with assessments of physical (seed size, weight, and moisture content) and physiological tests (germination rate, germination speed, and mean time of germination).Morphological characterization revealed that the thick, woody sclerotesta forms an impermeable barrier, while the embryos within are often underdeveloped at the time of seed maturity. Germination of the first year demonstrated that removing the sclerotesta significantly enhances germination rates, with naked seeds achieving a 70% germination rate at 30 °C. In the second year, soaking naked seeds in gibberellic acid at 200 ppm for 24 hours further promoted germination, though its effect was modest compared to sclerotesta removal (naked seed). This study also demonstrated that storing seeds for a year allowed embryos to complete their development, further improving germination outcomes. These findings suggested that mechanical removal of the sclerotesta, combined with optimal storage conditions, is an effective strategy for overcoming dormancy in C. revoluta seeds and soak time in gibberellic acid (200 ppm) or water for 24 hours could enhance germination as well.

Argyreia is the most recently evolved genus in the Convolvulaceae, and available information suggests that most species in this family produce seeds with physical dormancy (PY). Our aim was to understand the evolution of seed dormancy in this family via an investigation of dormancy, storage behaviour, morphology and anatomy of seeds of five Argyreia species from Sri Lanka. Imbibition, germination and dye tracking of fresh intact and manually scarified seeds were studied. Scanning electron micrographs and hand sections of the hilar area and the seed coat away from the hilar area were compared. Scarified and intact seeds of A. kleiniana , A. hirsuta and A. zeylanica imbibed water and germinated to a high percentage, but only scarified seeds of A. nervosa and A. osyrensis did so. Thus, seeds of the three former species are non-dormant (ND), while those of the latter two have physical dormancy (PY); this result was confirmed by dye-tracking experiments. Since >90% of A. kleiniana, A. hirsuta and A. zeylanica seeds survived desiccation to 10% moisture content (MC) and >90% of A. nervosa and A. osyrensis seeds with a dispersal MC of ~12% were viable, seeds of the five species were desiccation-tolerant. A. nervosa and A. osyrensis have a wide geographical distribution and PY, while A. kleiniana , A. hirsuta and A. zeylanica have a restricted distribution and ND. Although seeds of A. kleiniana are ND, their seed coat anatomy is similar to that of A. osyrensis with PY. These observations suggest that the ND of A. kleiniana , A. hirsuta and A. zeylanica seeds is the result of an evolutionary reversal from PY and that ND may be an adaptation of these species to the environmental conditions of their wet aseasonal habitats. [ABSTRACT FROM AUTHOR]

Understanding the relationships between seed traits and germination responses is crucial for assessing natural regeneration, particularly in threatened ecosystems like the seasonally dry tropical forest (SDTF). This study explored links between seed traits (mass, volume, moisture content, and dispersal type), germination responses (germinability, germination speed ( v ¯ ), time to 50% of germination (T50), synchrony, and photoblastism), and physical dormancy (PY) in 65 SDTF species under experimental laboratory conditions. We found that species with smaller seeds (low mass and volume) had higher v ¯ and reached T50 faster than species with larger seeds. For moisture content, species with lower moisture content had higher germinability and reached the T50 faster than seeds with high moisture content. Abiotic dispersed species germinated faster and reached the T50 in fewer days. Most of the SDTF species (60%) did not present PY, and the presence of PY was associated with seeds with lower moisture content. As for photoblastism (germination sensitivity to light), we classified the species into three ecological categories: generalists (42 species, non-photoblastic), heliophytes (18 species, positive photoblastic, germination inhibited by darkness), and sciadophytes (5 species, negative photoblastic, light inhibited germination). This study intends to be a baseline for the study of seed ecophysiology in the SDTF. [ABSTRACT FROM AUTHOR]

IntroductionPlant seeds from weeds and energy crops have the potential to survive anaerobic digestion (AD). Species able to form physically dormant, i.e., hardseeded (HS) seeds seem particularly resistant. However, it is not yet known to what extent the storage of the digestate after AD affects seed viability.MethodsSeed survival of five HS and six non-HS (NHS) species was investigated in three combinations of digestate storage (DS) and AD. First, untreated seeds were exposed to DS for maximum 12 weeks. To simulate short-circuited AD (ADshort) in biogas reactors, seeds were second subjected to lab-scale AD for 1 day before DS. Third, seeds of six species were exposed to full-scale AD (ADfull) followed by DS. Seed viability was determined using a combination of germination tests and tetrazolium staining. Viability was modeled as a function of exposure time.Results and discussionSeed viability was affected by DS, AD and AD + DS, but responses varied greatly between species and treatments. With increasing exposure time, viability decreased after a lag-phase, remained stable or even increased. The NHS species Cichorium intybus, Daucus carota, Echium vulgare, and Verbascum thapsus were most susceptible, with seed-killing close to 100% if DS was involved. The HS species Malva sylvestris, Melilotus albus and Melilotus officinalis were most resistant. They survived all treatments and were alive after 35 days of ADfull plus 3 months of DS. The resistance potential of the HS species Abutilon theophrasti and Malva alcea and of the NHS species Chenopodium album and two tomato varieties was intermediate. None of them survived ADfull + DS, but except A. theophrasti they were viable after ADshort + DS. With few exceptions, seed-killing by AD + DS was higher than that by AD alone. In conclusion, DS and AD + DS have the potential to reduce seed viability, but do not completely inactivate all species. Therefore, digestate can be contaminated with viable seeds and may lead to the spread of weeds, especially after a short-circuited AD. In order to ensure the sustainable use of digestates in terms of weeds, we recommend to investigate the factors contributing to seed inactivation and the quantity of seed introduced to AD.

Simple Summary: Seed-based restoration is likely to become less successful with climate change due to reduced seed germination and seedling emergence. Studying how native plant species respond to environmental stress using a whole life cycle approach can help predict climate change impacts on successful plant establishment. Therefore, the aim of this study was to understand how temperature and moisture stress affect seed germination and seedling emergence together with determining how soil moisture stress can impact the reproductive biology of plants. A native Australian legume species, Desmodium brachypodum A. Gray, was selected as a model species. The seed germination and seeding emergence were reduced by more than half when exposed to elevated temperatures and moisture stress. When the plants produced seeds under moisture stress, the duration of seed production and the number of produced seeds decreased. On the other hand, no differences were observed in the seed traits of those produced seeds. In conclusion, the reproductive output of D. brachypodum had low seed variability under moisture stress, which might be useful when sourcing seeds from climates with high variability. Even so, a reduction in the seed quantity under maternal moisture stress can impact the long-term survival of restored plant populations. Understanding how seed functional traits interact with environmental factors to determine seedling recruitment is critical to assess the impact of climate change on ecosystem restoration. This study focused on the effects of environmental factors on the mother plant during early plant life history stages and during seed development. Desmodium brachypodum A. Gray (large tick trefoil, Fabaceae) was used as a model species. Firstly, this study analyzed seed germination traits in response to temperature and moisture stress. Secondly, it investigated how seed burial depth interacts with temperature and soil moisture to influence seedling emergence traits. Finally, it determined if contrasting levels of post-anthesis soil moisture could result in changes in D. brachypodum reproductive biology and seed and seedling functional traits. The results showed that elevated temperature and moisture stress interacted to significantly reduce the seed germination and seedling emergence (each by >50%), while the seed burial improved the seedling emergence. Post-anthesis soil moisture stress negatively impacted the plant traits, reducing the duration of the reproductive phenology stage (by 9 days) and seed production (by almost 50%). Unexpectedly, soil moisture stress did not affect most seed or seedling traits. In conclusion, elevated temperatures combined with low soil moisture caused significant declines in seed germination and seedling emergence. On the other hand, the reproductive output of D. brachypodum had low seed variability under soil moisture stress, which might be useful when sourcing seeds from climates with high variability. Even so, a reduction in seed quantity under maternal moisture stress can impact the long-term survival of restored plant populations. [ABSTRACT FROM AUTHOR]

Many Astragalus species exhibit seeds with physical dormancy (PY), but little is known about the ecological context of this dormancy. We focused on A. maritimus and A. verrucosus, two threatened Sardinian endemic species inside the subgenus Trimeniaeus Bunge. Fresh seeds collected from the only two respective known populations were used to investigate the effect of mechanical scarification, heat shock, and water imbibition processes on PY release and germination. PY can be overcome through mechanical scarification of the water-impermeable seed coats, while no dormancy break was detected, nor a subsequent increase in seed germination due to fire-induced heat. This suggests that fire does not trigger dormancy release and seed germination in these species. The seeds tolerate relatively high heat shock temperatures (up to 120 and 100 °C for A. verrucosus and A. maritimus, respectively), but after 120 °C for 10 min, the number of dead seeds increases in both species. These facts suggest the capacity to develop a soil seed bank that can persist after fires and delay germination until the occurrence of optimal conditions. As regards water imbibition, both Astragalus species did not show the typical triphasic pattern, as germination started without further water uptake. This study emphasizes the significance of understanding germination processes and dormancy in threatened species. In fire-prone ecosystems, PY dormancy plays a crucial role in soil seed bank persistence, and it may be selectively influenced by post-fire conditions. Understanding such adaptations provides useful insights into conservation strategies. [ABSTRACT FROM AUTHOR]

Fabaceae produce seeds with water‐impermeable seed coats, i.e., physical dormancy (PY). We hypothesized that the proportion of PY seeds will increase with the dryness of the habitat, and some key seed ecological traits will be strongly associated with different levels of PY.Fresh seed of 25 Fabaceae species collected in northern India were used for imbibition and germination experiments to determine the proportion of seeds with PY and of nondormant (ND) seeds compared to their Sri Lankan congeners. Seed coat:seed mass ratio (SCR), 1000 seed weight, seed shape index (SSI), embryo type and median germination time of ND seeds were determined.Four imbibition and germination patterns were identified among seeds of the studied species. Seeds collected from Indian populations had a higher proportion of PY seeds than those of Sri Lankan populations. We identified a type of embryo called 'spatulate axile' that had not been identified before among the studied species. Species with ND seeds had a lower SCR and a higher SSI than those with PY.Our hypothesis was confirmed since populations from drier habitats in India produce a higher proportion of PY seeds than those from Sri Lanka. A low SCR ensures minimal resistance to germinating seeds, while seeds with a high SSI have a lower tendency to incorporate into the soil seed bank. Thus, these seed traits aid the fast germination of ND seeds, often dispersed just before the rainy season. [ABSTRACT FROM AUTHOR]

Understanding the relationships between seed traits and germination responses is crucial for assessing natural regeneration, particularly in threatened ecosystems like the seasonally dry tropical forest (SDTF). This study explored links between seed traits (mass, volume, moisture content, and dispersal type), germination responses (germinability, germination speed (v¯), time to 50% of germination (T50), synchrony, and photoblastism), and physical dormancy (PY) in 65 SDTF species under experimental laboratory conditions. We found that species with smaller seeds (low mass and volume) had higher v¯ and reached T50 faster than species with larger seeds. For moisture content, species with lower moisture content had higher germinability and reached the T50 faster than seeds with high moisture content. Abiotic dispersed species germinated faster and reached the T50 in fewer days. Most of the SDTF species (60%) did not present PY, and the presence of PY was associated with seeds with lower moisture content. As for photoblastism (germination sensitivity to light), we classified the species into three ecological categories: generalists (42 species, non-photoblastic), heliophytes (18 species, positive photoblastic, germination inhibited by darkness), and sciadophytes (5 species, negative photoblastic, light inhibited germination). This study intends to be a baseline for the study of seed ecophysiology in the SDTF.

Understanding how seed functional traits interact with environmental factors to determine seedling recruitment is critical to assess the impact of climate change on ecosystem restoration. This study focused on the effects of environmental factors on the mother plant during early plant life history stages and during seed development. Desmodium brachypodum A. Gray (large tick trefoil, Fabaceae) was used as a model species. Firstly, this study analyzed seed germination traits in response to temperature and moisture stress. Secondly, it investigated how seed burial depth interacts with temperature and soil moisture to influence seedling emergence traits. Finally, it determined if contrasting levels of post-anthesis soil moisture could result in changes in D. brachypodum reproductive biology and seed and seedling functional traits. The results showed that elevated temperature and moisture stress interacted to significantly reduce the seed germination and seedling emergence (each by >50%), while the seed burial improved the seedling emergence. Post-anthesis soil moisture stress negatively impacted the plant traits, reducing the duration of the reproductive phenology stage (by 9 days) and seed production (by almost 50%). Unexpectedly, soil moisture stress did not affect most seed or seedling traits. In conclusion, elevated temperatures combined with low soil moisture caused significant declines in seed germination and seedling emergence. On the other hand, the reproductive output of D. brachypodum had low seed variability under soil moisture stress, which might be useful when sourcing seeds from climates with high variability. Even so, a reduction in seed quantity under maternal moisture stress can impact the long-term survival of restored plant populations.

Many Astragalus species exhibit seeds with physical dormancy (PY), but little is known about the ecological context of this dormancy. We focused on A. maritimus and A. verrucosus, two threatened Sardinian endemic species inside the subgenus Trimeniaeus Bunge. Fresh seeds collected from the only two respective known populations were used to investigate the effect of mechanical scarification, heat shock, and water imbibition processes on PY release and germination. PY can be overcome through mechanical scarification of the water-impermeable seed coats, while no dormancy break was detected, nor a subsequent increase in seed germination due to fire-induced heat. This suggests that fire does not trigger dormancy release and seed germination in these species. The seeds tolerate relatively high heat shock temperatures (up to 120 and 100 °C for A. verrucosus and A. maritimus, respectively), but after 120 °C for 10 min, the number of dead seeds increases in both species. These facts suggest the capacity to develop a soil seed bank that can persist after fires and delay germination until the occurrence of optimal conditions. As regards water imbibition, both Astragalus species did not show the typical triphasic pattern, as germination started without further water uptake. This study emphasizes the significance of understanding germination processes and dormancy in threatened species. In fire-prone ecosystems, PY dormancy plays a crucial role in soil seed bank persistence, and it may be selectively influenced by post-fire conditions. Understanding such adaptations provides useful insights into conservation strategies.