Desiccation-sensitive Seeds Research Articles

Long-term seed storage for desiccation sensitive seeds in the marine foundation species Zostera marina L. (eelgrass)

Seagrass meadows are recognized as critical and among the most vulnerable habitats on the planet. There is an urgent need to develop techniques to restore and preserve these vital coastal ecosystems. So far little work has been done to develop effective long-term storage methods for desiccation sensitive seagrass seeds. In the present study, we developed a long-term seed storage method for desiccation sensitive seagrass seeds using Zostera marina L. as model species. During the storage, Z. marina seeds from the 0 °C treatments had lower seed loss percentages and high seed vigor, compared to the 4 °C treatments. Salinity significantly influenced seed vigor after storage. Seeds stored at a salinity of 40–50 psμ had the highest vigor. Wet storage at a salinity of 40–50 psμ and 0 °C was the optimal long-term storage condition, considering factors such as seed loss percentage, seed germination percentage, and seed germination value during or after the long-term storage. By controlling temperature and salinity, we could store Z. marina seeds for ca. 17 months because the collection of the seeds from reproductive shoots and maintain low seed losses and high seed vigor. The findings revealed the optimal conditions for long-term storage of desiccation sensitive Z. marina seeds and provided a useful reference for the establishment of Z. marina seed banks. Our results could also provide information to support Z. marina seagrass meadow restoration efforts using seeds.

The Cryobiotechnology of Oaks: An Integration of Approaches for the Long-Term Ex Situ Conservation of Quercus Species

Conventional dry seed storage is unlikely for about one third of all tree species (and nearly half of evergreen rain forest trees) as they probably produce desiccation sensitive (recalcitrant) seeds. Consequently, international ex situ conservation targets for threatened trees will be difficult to achieve without innovation, especially in cryobiotechnology. We assessed progress in the development of various cryobiotechnology approaches for the preservation of oaks (Quercus), which are keystone species of functioning landscapes, important to the bioeconomy and under increasing threats from the spread of pests and diseases under a changing climate. Various tissues of oaks can be used for banking, from pollen grains to embryo axes. Pollen from five oak species have been shown to be highly desiccation tolerant, making dry pollen storage at low temperatures (including in liquid nitrogen) a valuable technology to support conservation and breeding programs. Somatic embryo (SE) technology and/or shoot tip in vitro technology is available for 39 species, and SE cryopreservation is routinely performed on three commercial species and shoot tips cryopreservation successful in two more species. Seed embryonic axes are the preferred explants for oak ex situ conservation, with tissue survival and regeneration of plants after cryopreservation recorded for 14 and seven species respectively; although differential responses between the shoot and root meristems in the axes are known. Dormant bud preservation seems promising, but is under-researched. Overall, these results indicate the possibility of establishing an integrated platform for the ex situ conservation of oak species based on cryobiotechnology. Challenges of explant choice, optimization of methodologies and large-scale application do remain. However, multiple approaches for the cryopreservation of oak genetic resources are available and implementation programmes should not be delayed, particularly in the centres of species diversity.

Total lipid and fatty acid profiles of Coffea arabica endosperm and embryo tissues and their relationship to seed desiccation sensitivity

As seed chemical composition may lead to different responses during drying and other post-harvest operations, the objective of this study was to determine the effect of drying rate (slow and rapid) and the concentration and composition of lipids in the embryo and endosperm tissues of Coffea arabica seeds on desiccation tolerance/ sensitivity. The total concentration of lipids and the composition of fatty acids were evaluated in isolated embryos and endosperms, and in whole (intact) seeds. Embryos had a higher total lipid concentration (23%) than endosperm tissue (8%). Linoleic acid was the predominant fatty acid, with concentrations of 48% in the endosperm and 34% in the embryo tissues. Although rapid or slow drying did not change the fatty acid profile in the embryos or endosperms, the palmitic and linoleic acid concentrations varied significantly between the embryo and endosperm. The predominance of linoleic acid in the endosperm supports the hypothesis that the endosperm tissue may be an important source of damage to the seed and may advance seed deterioration. This indicates that unsaturated fatty acids may have a greater effect on sensitivity to desiccation than the percentage of total lipids.

Effects of seed priming on germination and seedling growth of desiccation-sensitive seeds from Mexican tropical rainforest.

Seed priming increases the vigor of seeds and seedlings through metabolic and biochemical processes occurring during controlled hydration, followed by dehydration. In the field, seeds are exposed to hydration-dehydration events in and on the soil after dispersal, as in seed priming. Nevertheless, seed priming has been sparsely tested on desiccation-sensitive seeds, which are vulnerable to climate change effects. We evaluated the effect of two priming methods on seeds from two tropical rainforest species: Cupania glabra and Cymbopetalum baillonii. For hydropriming, the seeds were fully hydrated and then dehydrated to three dehydration levels. For natural priming, the seeds were buried for 12days in either closed forest or forest gap. Primed seeds were sown in 1% agar medium and placed in an environmental chamber. The growth of the seedlings from the highest germination priming treatments was evaluated for 1year in the field. Our results showed that for C. glabra and C. baillonii, hydroprimed seeds varied in their germination response, depending on the degree of their dehydration. However, for C. baillonii, hydropriming seems to invigorate seeds, compared to non-imbibed seeds of the same dehydration level. Natural priming increased germination speed in both species without any difference between closed forest and forest gap. Moreover, seeds with natural priming had a higher final germination percentage than seeds with hydropriming. Seedlings from seeds with natural priming showed a higher growth rate than the controls in both species, whereas hydropriming produced a similar effect in C. glabra. Both priming methods could be used for restoration practices with the studied species, natural priming being a novel method. The ecological implications of priming in desiccation sensitive seeds are discussed in this study.

Epicotyl morphophysiological dormancy and storage behaviour of seeds of Strychnos nux-vomica, Strychnos potatorum and Strychnos benthamii (Loganiaceae)

AbstractWe hypothesized that Strychnos nux-vomica and Strychnos potatorum in seasonal tropical ecosystems have dormant desiccation-tolerant seeds, while those of Strychnos benthamii growing in aseasonal wet habitats have non-dormant desiccation-sensitive seeds. Germination, imbibition, the effect of gibberellic acid on germination and changes in the embryo to seed length ratio (E:S) during incubation were determined for the three species. Seed storage behaviour was identified with the hundred seed test. Time taken for epicotyl emergence was recorded. Radicle emergence of S. nux-vomica, S. potatorum and S. benthamii at 25°C under light/dark conditions (12/12 h) was completed within 76, 49 and 11 d, respectively. S. nux-vomica and S. potatorum seeds incubated on GA3 germinated to a higher percentage than non-treated seeds. E:S of S. nux-vomica, S. potatorum and S. benthamii had increased by 38.2, 34.5 and 25.5%, respectively, at radicle emergence. Shoot emergence of S. nux-vomica, S. potatorum and S. benthamii was observed after 76, 74 and 45 d from radicle emergence, respectively. Thus, it can be concluded that the seeds of all three species have epicotyl morphophysiological dormancy. Hundred seed tests revealed that S. nux-vomica and S. potatorum seeds were desiccation-tolerant, while those of S. benthamii were desiccation-sensitive. Our study showed that species from seasonal habitats (S. nux-vomica and S. potatorum) have desiccation-tolerant morphophysiologically dormant seeds, while those from an aseasonal habitat (S. benthamii) have desiccation-sensitive morphophysiologically dormant seeds, revealing that their dormancy and desiccation tolerance behaviour are adaptations to their environment.

Macroevolutionary patterns in seed component mass and different evolutionary trajectories across seed desiccation responses.

Seed coat and seed reserve show substantial mass variation, play different roles in plant life strategies and are shaped by different selective forces. However, remarkably little is known about the macroevolution of the relative allocation in seed components and its influence on important ecophysiological processes. Using phylogenetic comparative methods and evolutionary modelling approaches, we modelled mass changes in seed components along individual lineages for 940 species and compared the patterns across seed desiccation responses. Seed component allocation was driven primarily by changes in reserve mass rather than coat mass, as evolutionary rates in reserve mass significantly outpaced those in coat mass. Although the scaling patterns between reserve mass and coat mass were similar across desiccation responses, desiccation-sensitive seeds allocated more and evolved faster in reserve compared to desiccation-tolerant seeds. The findings emphasize the relative importance of reserve to coat in the evolution of plant reproductive strategies, revealing potential ecological advantages gained by enlarged reserve. As the first quantification of the evolutionary tempo and mode of seed component mass, our study allows a detailed interpretation of evolutionary pathways underlying seed storage behaviours and advances the understanding of the evolution of desiccation sensitivity in seeds.

Peptide-Bound Methionine Sulfoxide (MetO) Levels and MsrB2 Abundance Are Differentially Regulated during the Desiccation Phase in Contrasted Acer Seeds.

Norway maple and sycamore produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. Drying affects reduction and oxidation (redox) status in seeds. Oxidation of methionine to methionine sulfoxide (MetO) and reduction via methionine sulfoxide reductases (Msrs) have never been investigated in relation to seed desiccation tolerance. MetO levels and the abundance of Msrs were investigated in relation to levels of reactive oxygen species (ROS) such as hydrogen peroxide, superoxide anion radical and hydroxyl radical (•OH), and the levels of ascorbate and glutathione redox couples in gradually dried seeds. Peptide-bound MetO levels were positively correlated with ROS concentrations in the orthodox seeds. In particular, •OH affected MetO levels as well as the abundance of MsrB2 solely in the embryonic axes of Norway maple seeds. In this species, MsrB2 was present in oxidized and reduced forms, and the latter was favored by reduced glutathione and ascorbic acid. In contrast, sycamore seeds accumulated higher ROS levels. Additionally, MsrB2 was oxidized in sycamore throughout dehydration. In this context, the three elements •OH level, MetO content and MsrB2 abundance, linked together uniquely to Norway maple seeds, might be considered important players of the redox network associated with desiccation tolerance.

Seed selection and storage with nano-silver and copper as potential antibacterial agents for the seagrass Zostera marina: implications for habitat restoration

Globally, seagrass meadows are extremely important marine ecosystems that are disappearing at an alarming rate. Therefore, research into seagrass restoration has become increasingly important. Various strategies have been used in Zostera marina L. (eelgrass) restoration, including planting seeds. To improve the efficiency of restoration by planting seeds, it is necessary to select high-quality seeds. In addition, a suitable antibacterial agent is necessary for wet storage of desiccation sensitive seeds to reduce or inhibit microorganism infection and seed decay. In the present study, an efficient method for selecting for high-quality eelgrass seeds using different specific gravities of salt water was developed, and potential antibacterial agents (nano-silver and copper sulfate) for seed storage were assessed. The results showed that the highest proportion of intact seeds (72.91 ± 0.50%) was recorded at specific gravities greater than 1.20. Therefore, specific gravities greater than 1.20 can be used for selecting high-quality eelgrass seeds. During seed storage at 0 °C, the proportion of intact seeds after storage with nano-silver agent was over 90%, and also higher than 80% with copper sulfate agent, which was significantly higher than control treatments. The findings revealed a potential selection method for high-quality seeds and long-term seed storage conditions for Z. marina, which could facilitate conservation and habitat restoration.

The influence of seed morpho-physiological and meristematic cell wall traits on seed desiccation sensitivity in three angiosperm tree species

The structure and composition of physical barriers to water loss such as the seed coat and embryo meristematic cell walls (CWs) can potentially affect the rate and topographical patterns of water loss and consequently desiccation sensitivity in recalcitrant seeds. This study provides insights into the phenomenon of seed recalcitrance, by investigating the influence of seed morpho-physiological and (root) meristematic CW structure and composition on seed desiccation sensitivity in three recalcitrant-seeded angiosperm tree species, viz. a mangrove tree, Avicennia marina (Forssk.) Vierh. (Acanthaceae); a sub-tropical forest tree, Trichilia dregeana Sond. (Meliaceae); and a tropical fruit tree, Artocarpus heterophyllus Lamk. (Moraceae). Whole seed water content (WC), dry mass (DM), seed coat ratio (SCR), and root meristem CW thickness and composition were related to embryo desiccation sensitivity and drying rate in each of the three species. The embryos of the heavier A. marina and A. heterophyllus seeds were faster drying and more desiccation sensitive than the relatively lighter T. dregeana seeds. The apportioning of more water towards the embryo in A. marina and A. heterophyllus than in T. dregeana, may be an evolutionary consequence of their faster drying rate and greater desiccation sensitivity. In both A. marina and A. heterophyllus, the ratio of highly esterified to unesterified pectins was lower, and the meristem CW thickness was greater than in T. dregeana. The thick, rigid CWs of A. marina and A. heterophyllus probably contributes to their greater desiccation sensitivity, since desiccation tolerance in vegetative tissues has previously been associated with thin flexible CWs. Seed water distribution patterns and CW thickness and rigidity may be useful indicators of seed desiccation sensitivity. The degree and nature to which these morpho-physiological and ultrastructural traits influence seed desiccation sensitivity in individual species may be a consequence of habitat-specific evolutionary pressures.

Assessing seed desiccation responses of native trees in the Caribbean

Native trees from the Caribbean were tested for seed desiccation responses, by adapting the “100-seed test” protocol. Ninety-seven seed lots of 91 species were collected in the Dominican Republic and tested for germination immediately after collecting, and after drying and moist storage. Seed desiccation sensitivity was assessed as a continuous variable (Viability Loss Index; VLI), based on seed germination values before and after drying. The results were compared with predictions of seed desiccation responses based on seed lot traits (initial moisture content and thousand-seed weight) and with those of published predictive models based on plant and seed traits. VLI could be calculated for seed lots of 40 species. 80% of these seed lots showed consistent results among experiments and predictive models. Issues on the set up of the experiments were discussed, as well as the species for which experimental results and predictions led to contrasting results. Overall, the “100-seed test” confirmed to be an effective tool for assessing seed desiccation responses of a diverse under-investigated woody flora, guiding the seed conservation of trees and their use in reforestation programmes. In addition, by providing new data, it might improve the performance of available predictive models.

Environmental Correlates for Seed Desiccation Sensitivity of New Caledonian Plant Species1

Efficient in situ and ex situ conservation strategies are urgently needed in biodiversity hotspots, where high concentrations of endemic plant species are undergoing exceptional loss of habitat. In particular, determining seed desiccation sensitivity is a key prerequisite to design storage methods useful for ex situ programs. In this study, we explored seed desiccation sensitivity and its link with phenological and morphological traits as well as with the environmental variables for 45 New Caledonian plant species. Desiccation sensitivity was quantified through RH50, that is, the relative humidity at which 50% of initial viable seeds died. RH50 was found to be positively associated with the initial seed water content, seed mass, precipitation seasonality, precipitation of the warmest quarter, and presence in rainforest habitats. In contrast, the ability of species to endure desiccation increased in drier habitats such as dry forest. We also found that desiccation sensitivity was consistent at the genus level. These new data provide the basis to establish conservation plans for a large array of plant species in New Caledonia. Moreover, this study may help us to better understand the underlying mechanisms of desiccation sensitivity and to predict desiccation sensitivity of other taxa within the New Caledonian flora on the basis of taxonomy, functional traits and environmental features.

Induction of desiccation tolerance in desiccation sensitive Citrus limon seeds.

Many economically important perennial species bear recalcitrant seeds, including tea, coffee, cocoa, mango, citrus, rubber, oil palm and coconut. Orthodox seeds can be dried almost completely without losing viability, but so‐called recalcitrant seeds have a very limited storage life and die upon drying below a higher critical moisture content than orthodox seeds. As a result, the development of long‐term storage methods for recalcitrant seeds is compromised. Lowering this critical moisture content would be very valuable since dry seed storage is the safest, most convenient and cheapest method for conserving plant genetic resources. Therefore, we have attempted to induce desiccation tolerance (DT) in the desiccation sensitive seeds of Citrus limon. We show that DT can be induced by paclobutrazol (an inhibitor of gibberellin biosynthesis) and we studied its associated transcriptome to delineate the molecular mechanisms underlying this induction of DT. Paclobutrazol not only interfered with gibberellin related gene expression but also caused extensive changes in expression of genes involved in the biosynthesis and signaling of other hormones. Paclobutrazol induced a transcriptomic switch encompassing suppression of biotic‐ and induction of abiotic responses. We hypothesize that this is the main driver of the induction of DT by paclobutrazol in C. limon seeds.

Artificial Seed for Short-Term Storage:Using Nodal Buds in Aquilaria malaccensis Lam

Artificial seed technology is known to be the best alternative for short-term storage of plant germplasm in recalcitrant species. Aquilaria malaccensis , being a recalcitrant seeded tree, possesses seasonal and highly desiccation-sensitive seeds which lose viability with slight decrease in their moisture content, hence storage becomes a difficult task. The present study deals with short-term storage of A. malaccensis nodal buds through artificial seed technology. Nodal buds encapsulated with 2.5% sodium alginate and 100 mM calcium chloride, and polymerized for 40 min were found suitable for artificial seed preparation. Maximum regeneration rate of 83.3% and 75.0% was observed from encapsulated nodal buds stored at 4°C and 23 ± 2°C respectively, for 10 days. Storage was possible for a period of 60 days at 4°C and 50 days at 23 ± 2°C with average regeneration rate of 8.3% and 16.7% respectively.

The Occurrence of Peroxiredoxins and Changes in Redox State in Acer platanoides and Acer pseudoplatanus During Seed Development

Norway maple (Acer platanoides L.) and sycamore (A. pseudoplatanus L.) are genetically closely related species that produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. Norway maple and sycamore seeds were analyzed during their development from the 14th to 24th weeks after flowering (WAF) and 11th to 21st WAF, respectively, to explore redox-related biochemical properties related to their contrasting physiology. Selected similar stages of seed development were characterized during the course of gradual decreasing water content in both seed types. The levels of protein and non-protein thiols peaked at the 18th WAF in Norway maple embryonic axes, whereas these levels constantly increased in maturing sycamore seeds. The glutathione half-cell reduction potential revealed that the cell environment adopted a more oxidized state in sycamore seeds. Peroxiredoxins (Prxs), including cytosolic/nuclear 1-Cys-Prx, cytosolic PrxIIC, mitochondrial PrxIIE, and plastidic PrxIIF, 2-Cys-Prx, and PrxQ, were detected in both species, but Norway maple embryonic axes contained higher levels of PrxIIC and PrxIIE, two Prxs with the highest peroxide detoxification potential in Arabidopsis. Redox proteomics revealed that 2-Cys-Prx was present in reduced form in both species, whereas 1-Cys-Prx was reduced uniquely in Norway maple seeds. Several enzymes, including glucose and ribitol dehydrogenase as well as fructose-bisphosphate aldolase, were oxidation-sensitive at all developmental stages in sycamore embryonic axes. Redox signaling as manifested by reactive oxygen species signals, and the oxidation of protein thiols to disulfides are discussed with respect to their significance in determining orthodox or recalcitrant seed characteristics.

Zygotic embryo cell wall responses to drying in three gymnosperm species differing in seed desiccation sensitivity.

Plant cell walls (CWs) are dynamic in that they can change conformation during ontogeny and in response to various stresses. Though seeds are the main propagatory units of higher plants, little is known of the conformational responses of zygotic embryo CWs to drying. This study employed cryo-scanning electron microscopy to compare the effects of desiccation on zygotic embryo CW morphology across three gymnosperm species that were shown here to differ in seed desiccation sensitivity: Podocarpus henkelii (highly desiccation-sensitive), Podocarpus falcatus (moderately desiccation-sensitive), and Pinus elliottii (desiccation-tolerant). Fresh/imbibed (i.e. fresh Podocarpus at shedding and imbibed Pi. elliottii) embryos showed polyhedral cells with regular walls, typical of turgid cells with an intact plasmalemma. Upon desiccation to c. 0.05gg-1 (dry mass basis), CWs assumed an undulating conformation, the severity of which appeared to depend on the amount and type of dry matter accumulated. After desiccation, intercellular spaces between cortical cells in all species were comparably enlarged relative to those of fresh/imbibed embryos. After rehydration, meristematic and cotyledonary CWs of P. henkelii and meristematic CWs of P. falcatus remained slightly undulated, suggestive of plasmalemma and/or CW damage, while those of Pi. elliottii returned to their original conformation. Cell areas in dried-rehydrated P. henkelii root meristem and cotyledon were also significantly lower than those from fresh embryos, suggesting incomplete recovery, even though embryo water contents were comparable between the two states. Electrolyte leakage measurements suggest that the two desiccation-sensitive species incurred significant plasmalemma damage relative to the tolerant species upon desiccation, in agreement with the CW abnormalities observed in these species after rehydration. Immunocytochemistry studies revealed that of the four CW epitopes common to embryos of all three species, an increase in arabinan (LM6) upon desiccation and rehydration in desiccation-tolerant Pi. elliottii was the only difference, although this was not statistically significant. Seed desiccation sensitivity in species like P. henkelii and P. falcatus may therefore be partly based on the inability of the plasmalemma and consequently CWs of dried embryos to regain their original conformation following rehydration.

Evolutionary ecophysiology of seed desiccation sensitivity.

Desiccation sensitive (DS) seeds do not survive dry storage due to their lack of desiccation tolerance. Almost half of the plant species in tropical rainforests produce DS seeds and therefore the desiccation sensitivity of these seeds represents a problem for and long-term biodiversity conservation. This phenomenon raises questions as to how, where and why DS (desiccation sensitive)-seeded species appeared during evolution. These species evolved probably independently from desiccation tolerant (DT) seeded ancestors. They adapted to environments where the conditions are conducive to immediate germination after shedding, e.g. constant and abundant rainy seasons. These very predictable conditions offered a relaxed selection for desiccation tolerance that eventually got lost in DS seeds. These species are highly dependent on their environment to survive and they are seriously threatened by deforestation and climate change. Understanding of the ecology, evolution and molecular mechanisms associated with seed desiccation tolerance can shed light on the resilience of DS-seeded species and guide conservation efforts. In this review, we survey the available literature for ecological and physiological aspects of DS-seeded species and combine it with recent knowledge obtained from DT model species. This enables us to generate hypotheses concerning the evolution of DS-seeded species and their associated genetic alterations.

Seed Longevity of Five Tropical Species From South-Eastern Mexico: Changes in Seed Germination During Storage

To design conservation strategies, the extent of plant richness of tropical forests needs to be characterized in terms of their seed longevity. In this study, we examined the potential seed longevity, that is, storage ex situ, of species from south-eastern Mexico: Chamaedorea glaucifolia, Cymbopetalum baillonii, Magnolia mexicana, Nectandra coriacea, and Ternstroemia tepezapote. Immediately after collection, seeds were stored at different temperatures (≤23℃). We evaluated seed germination after different storage durations. Seed water content (WC) was determined for each period. Seed desiccation sensitivity was determined as WC50, which is the WC at which the initial seed viability decreases to 50%; further, the time required to reach WC50 was also determined. Subsequently, we analyzed the relations between seed functional traits with other morphological and functional traits, along with the weather characteristics of their respective habitat. All of the studied species had short-lived seeds; they exhibited desiccation sensitivity after storage with differences across the species. Additionally, C. baillonii exhibited differences in seed desiccation sensitivity across 2 years of seed collection. Interaction was observed between storage time and storage temperature: Seeds exhibited less deterioration at 15℃ in C. glaucifolia and C. baillonii and at 5℃ in M. mexicana and N. coriacea. Seed storage behavior is discussed in this article. Finally, a relationship determined between germination traits, and seed WC, embryo size, endosperm amount, and rain and temperature patterns in the month of seed dispersal explained the limited longevity of the studied species.

Seed germination of coastal monsoon vine forest species in the Northern Territory, Australia, and contrasts with evergreen rainforest

Seed germination traits of seasonal rainforest species differ from permanently moist evergreen rainforest species due to the prolonged seasonal drought. We investigated whether seed germination traits used to categorise evergreen rainforest species into pioneer and climax guilds were applicable to seasonal rainforest species. Seed dormancy, light requirements for germination and seed storage types of five climax and thirteen pioneer species of a coastal vine thicket were studied. Results were compared with published studies of evergreen rainforest species. Evergreen rainforest pioneer species are typically dormant, require light to germinate and tolerate desiccation, whereas climax species are typically non-dormant, tolerate shade during germination and are sensitive to desiccation. In seasonal rainforest we found that a high proportion of pioneer species had seeds that were non-dormant (62%), and a high proportion of pioneer species germinated equally well in light and dark conditions. In seasonal rainforest, we found that the majority of climax species had desiccation tolerant seeds, whereas in evergreen rainforest the proportion of climax species producing desiccation sensitive seeds is equal to or greater than the proportion of species with desiccation tolerant seeds. In seasonal rainforest species physical, physiological and epicotyl dormancy types were found. Generally, for seasonal rainforest species, the prevalent form of dormancy in pioneer species was physical dormancy whereas physiological dormancy was most common in evergreen rainforest pioneer species with dormancy. Our results suggest that the contrasting seed biology traits that typically apply to pioneer and climax species of evergreen rainforest species don’t typically apply to seasonal rainforest species.

A role for fruit structure in seed survival and germination of Swartzia langsdorffii Raddi beyond dispersal.

Diaspore structure has been hypothesised to play a role in seed viability and/or germination of recalcitrant seeds, especially for Swartzia langsdorffii. Thus, this work aims to (i) investigate the insitu contribution of pericarp and aril on seed viability and germination, and (ii) identify morphoanatomical traits of S.langsdorffii diaspores that allow its desiccation-sensitive seeds to remain viable. The role of the pericarp and aril in seed survival and germination was investigated by placing the whole fruit, whole seeds (arillate seed) and bare seeds (without aril) in soil in the forest understorey, assessing germination, emergence, dead, firm and predated seeds, and water content of pericarps, arils and seeds. Correlation analysis was performed between environmental variables and physiological parameters. Histochemical features of diaspores were also investigated. Pericarp water content fell after several months, while the aril maintained its water content. Seeds did not lose water even without the presence of the pericarp and aril. However, presence of the pericarp promoted seed water content, viability and germination long after dispersal. The embryo had a thickened outer periclinal cell wall. Pericarp and aril are not essential to prevent water loss in seeds, but do help to retain seed moisture, favouring viability maintenance and promoting germination during the rainy season. Morphoanatomical features of seeds are suggested as main factors that reduce water loss. Survival of these desiccation-sensitive seeds upon dispersal during the dry season appears to be facilitated by multiple diaspore features that prevent viability loss.

Taxonomic affinity, habitat and seed mass strongly predict seed desiccation response: a boosted regression trees analysis based on 17 539 species.

Seed desiccation response plays an important role in plant regeneration ecology, and has significant implications for species conservation. The majority of seed plants produce desiccation-tolerant (orthodox) seeds, whilst comparatively few produce desiccation-sensitive (recalcitrant) seeds that are unable to survive dehydration, and which cannot be conserved in traditional seed banks. This study develops a set of models to predict seed desiccation response in unstudied species. Taxonomy, trait, location and climate data were compiled to form a global data set of 17 539 species. Three boosted regression trees models were then developed to predict species' seed desiccation responses based on habitat and trait information for the species, and the seed desiccation responses of close relatives (either members of the same genus, family or order, depending on the model). Ten-fold cross-validation was used to test model predictive success. The utility of the models was then demonstrated by predicting seed desiccation response for two floras: Ecuador, and Britain and Ireland. The three models had varying success rates for identifying the desiccation-sensitive species: 89 % for the genus-level model, 79 % for the family-level model and 60 % for the order-level model. The most important predictor variables were the seed desiccation responses of a species' relatives, seed mass and annual precipitation. It is predicted that 10 % of seed plants from Ecuador and 1.2 % of those from Britain and Ireland produce desiccation-sensitive seeds. Due to data availability, prediction accuracy is likely to be higher for the British and Irish flora, where it is estimated that a desiccation-sensitive species had a 96.7 % chance of being correctly identified, compared with 80.8 % in the Ecuador flora. These models can utilize existing data to predict species' likely seed desiccation responses, providing a gap-filling tool for global studies of plant traits, as well as critical decision-making support for plant conservation activities.