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Reactive oxygen species (ROS) are considered to be detrimental to seed viability. However, recent studies have demonstrated that ROS have key roles in seed germination particularly in the release of seed dormancy and embryogenesis, as well as in protection from pathogens. This review considers the functions of ROS in seed physiology. ROS are present in all cells and at all phases of the seed life cycle. ROS accumulation is important in breaking seed dormancy, and stimulating seed germination and protection from pathogens. However, excessive ROS accumulation can be detrimental. Therefore, knowledge of the mechanisms by which ROS influence seed physiology will provide insights that may not only allow the development of seed quality markers but also help us understand how dormancy can be broken in several recalcitrant species. Reactive oxygen species have a dual role in seed physiology. Understanding the relative importance of beneficial and detrimental effects of ROS provides great scope for the improvement and maintenance of seed vigour and quality, factors that may ultimately increase crop yields.

Trait-based approaches have improved our understanding of plant evolution, community assembly and ecosystem functioning. A major challenge for the upcoming decades is to understand the functions and evolution of early life-history traits, across levels of organization and ecological strategies. Although a variety of seed traits are critical for dispersal, persistence, germination timing and seedling establishment, only seed mass has been considered systematically. Here we suggest broadening the range of morphological, physiological and biochemical seed traits to add new understanding on plant niches, population dynamics and community assembly. The diversity of seed traits and functions provides an important challenge that will require international collaboration in three areas of research. First, we present a conceptual framework for a seed ecological spectrum that builds upon current understanding of plant niches. We then lay the foundation for a seed-trait functional network, the establishment of which will underpin and facilitate trait-based inferences. Finally, we anticipate novel insights and challenges associated with incorporating diverse seed traits into predictive evolutionary ecology, community ecology and applied ecology. If the community invests in standardized seed-trait collection and the implementation of rigorous databases, major strides can be made at this exciting frontier of functional ecology.

• Heteromorphic diaspores (fruits and seeds) are an adaptive bet-hedging strategy to cope with spatiotemporally variable environments, particularly fluctuations in favourable temperatures and unpredictable precipitation regimes in arid climates. • We conducted comparative analyses of the biophysical and ecophysiological properties of the two distinct diaspores (mucilaginous seed (M⁺) vs indehiscent (IND) fruit) in the dimorphic annual Aethionema arabicum (Brassicaceae), linking fruit biomechanics, dispersal aerodynamics, pericarp-imposed dormancy, diaspore abscisic acid (ABA) concentration, and phenotypic plasticity of dimorphic diaspore production to its natural habitat and climate. • Two very contrasting dispersal mechanisms of the A. arabicum dimorphic diaspores were revealed. Dehiscence of large fruits leads to the release of M⁺ seed diaspores, which adhere to substrata via seed coat mucilage, thereby preventing dispersal (antitelechory). IND fruit diaspores (containing nonmucilaginous seeds) disperse by wind or water currents, promoting dispersal (telechory) over a longer range. • The pericarp properties confer enhanced dispersal ability and degree of dormancy on the IND fruit morph to support telechory, while the M⁺ seed morph supports antitelechory. Combined with the phenotypic plasticity to produce more IND fruit diaspores in colder temperatures, this constitutes a bet-hedging survival strategy to magnify the prevalence in response to selection pressures acting over hilly terrain.

Structural organization of organs in multicellular organisms occurs through intricate patterning mechanisms that often involve complex interactions between transcription factors in regulatory networks. For example, INDEHISCENT (IND), a basic helix-loop-helix (bHLH) transcription factor, specifies formation of the narrow stripes of valve margin tissue, where Arabidopsis thaliana fruits open on maturity. Another bHLH transcription factor, SPATULA (SPT), is required for reproductive tissue development from carpel margins in the Arabidopsis gynoecium before fertilization. Previous studies have therefore assigned the function of SPT to early gynoecium stages and IND to later fruit stages of reproductive development. Here we report that these two transcription factors interact genetically and via protein-protein contact to mediate both gynoecium development and fruit opening. We show that IND directly and positively regulates the expression of SPT, and that spt mutants have partial defects in valve margin formation. Careful analysis of ind mutant gynoecia revealed slight defects in apical tissue formation, and combining mutations in IND and SPT dramatically enhanced both single-mutant phenotypes. Our data show that SPT and IND at least partially mediate their joint functions in gynoecium and fruit development by controlling auxin distribution and suggest that this occurs through cooperative binding to regulatory sequences in downstream target genes.

Propagule dispersal is an integral part of the life cycle of seagrasses; important for colonising unvegetated areas and increasing their spatial distribution. However, to understand recruitment success, seed dispersal and survival in habitats of different complexity remains to be quantified. We tested the single and synergistic effects of three commonly distributed ecosystem engineers-eelgrass (Zostera marina), oysters (Magellana gigas) and blue mussels (Mytilus edulis)-on trapping of Z. marina seeds in a hydraulic flume under currents. Our results suggest that seed retention increases with habitat complexity and further reveal insights into the underlying mechanisms. In eelgrass canopy, trapping occurred mostly through direct blocking of a seed's pathway, while trapping in bivalve patches was mainly related to altered hydrodynamics in the lee side, i.e. behind each specimen. With increasing flow velocity (24-30 cm s-1 in eelgrass canopy, 18-30 cm s-1 in bivalve patches), modifications of the sediment surface through increased turbulence and erosive processes became more important and resulted in high seed trapping rates. Furthermore, we show that while monospecific patches of seagrass and bivalves had different trapping optima depending on flow velocities, intermixing resulted in consistently high trapping rates throughout the investigated hydrodynamic gradient. Our results highlight the importance of positive interactions among ecosystem engineers for seed retention and patch emergence in eelgrass.

Cynomorium songaricum Rupr. first described by Carl Johann (Ivanovič) Ruprecht in 1840 is a desert parasitic plant that mainly parasitizes the roots of Nitraria L. (especially of Nitraria tangutorum Bobrov., Nitraria sibirica Pall.). During seed maturation, C. songaricum releases a distinct smell, and its seeds are round and dust-like. Previous studies indicated that most parasitic plants produce small seeds, which are primarily dispersed by the wind. Recent studies reveal the significant role of animals in the seed dispersal of parasitic plants. In this study, we combined (1) the direct observation of the seed dispersal of C. songaricum , and (2) the indoor breeding of beetles and ants to assess the viability of seeds, clarify the seed dispersal system, and explore the mechanisms by which the seeds attract dispersal agents. By a population study, we identified beetles ( Mantichorula semenowi Reitter, 1888) and ants ( Messor desertora He & Song, 2009) as the primary seed dispersal agents for the C. songaricum . These plants rely on the visits from these agents to transfer their seeds near the roots of the host plant, Nitraria L.. The release of a distinct volatile compound from C. songaricum seeds attracts M. semenowi and M. desertora to consume and/or transport the seeds. This study provides the first evidence of a multi-medium and inter-species seed dispersal system in the C. songaricum . This study elucidates the role of invertebrates in the seed dispersal of desert parasitic plants. We propose that the two seed dispersal agents play distinct roles in the sequential seed dispersal of C. songaricum , representing two key stages in the overall seed dispersal mechanism.

Seed arrival is a limiting factor for the regeneration of diverse tropical forests and may be an important mechanism that drives patterns of tree species' distribution. Here we quantify spatial and seasonal variation in seed rain of secondary forests in southern Bahia, Brazil. We also examine whether secondary forest age enhances seed dispersal and whether seed rain density and diversity in secondary forests decay with distance from mature forest. Across a chronosequence of 15 pairs of mature and secondary forests, 105 seed traps were installed and monitored for one year. We tested the effects of secondary forest age, distance from mature forest, and seasonality on monthly seed rain density, diversity, seed dispersal mode, and diaspore size. We found that secondary forest age had strong, positive effects on the diversity of seed rain, which was generally higher during the wet season. Moreover, contrasting patterns among diversity indices revealed that seeds of rare species occurred more often in 40 yr old secondary forests and mature forests. While the proportion of biotically and abiotically dispersed seeds did not change significantly with distance from mature forest across all forest age classes, we found that biotically dispersed seeds contributed disproportionately more to seed rain diversity. Our results emphasize the importance of biotic dispersal to enhance diversity during secondary succession and suggest that changes in secondary forest structure have the potential to enhance the diversity of tropical secondary forests, principally by increasing dispersal of rare species.

Species interaction networks are traditionally explored as discrete entities with well-defined spatial borders, an oversimplification likely impairing their applicability. Using a multilayer network approach, explicitly accounting for inter-habitat connectivity, we investigate the spatial structure of seed–dispersal networks across the Gorongosa National Park, Mozambique. We show that the overall seed–dispersal network is composed by spatially explicit communities of dispersers spanning across habitats, functionally linking the landscape mosaic. Inter-habitat connectivity determines spatial structure, which cannot be accurately described with standard monolayer approaches either splitting or merging habitats. Multilayer modularity cannot be predicted by null models randomizing either interactions within each habitat or those linking habitats; however, as habitat connectivity increases, random processes become more important for overall structure. The importance of dispersers for the overall network structure is captured by multilayer versatility but not by standard metrics. Highly versatile species disperse many plant species across multiple habitats, being critical to landscape functional cohesion. Species interaction networks have been usually delimited by perceived habitat borders. Here, seed-dispersal is analyzed as a regional multilayer network of interconnected habitats, highlighting the key role of versatile dispersers for the functional cohesion of the whole Gorongosa landscape.

The environment during seed production has major impacts on the behaviour of progeny seeds. It can be shown that for annual plants temperature perception over the whole life history of the mother can affect the germination rate of progeny, and instances have been documented where these affects cross whole generations. Here we discuss the current state of knowledge of signal transduction pathways controlling environmental responses during seed production, focusing both on events that take place in the mother plant and those that occur directly as a result of environmental responses in the developing zygote. We show that seed production environment effects are complex, involving overlapping gene networks active independently in fruit, seed coat, and zygotic tissues that can be deconstructed using careful physiology alongside molecular and genetic experiments.

Main conclusionDifferences in dispersal and dormancy of heteromorphic diaspores of Aegilos tauschii may increase its flexibility to invade/occupy weedy unpredictable habitats by spreading risk in space and time.In plant species that produce dimorphic seeds, there often is a negative relationship between dispersal and dormancy, with high dispersal–low dormancy in one morph and low dispersal–high dormancy in the other, which may function as a bet-hedging strategy that spreads the risk of survival and ensures reproductive success. However, the relationship between dispersal and dormancy and its ecological consequences in invasive annual grasses that produce heteromorphic diaspores is not well studied. We compared dispersal and dormancy responses of diaspores from the basal (proximal) to the distal position on compound spikes of Aegilops tauschii, an invasive grass with heteromorphic diaspores. Dispersal ability increased and degree of dormancy decreased as diaspore position on a spike increased from basal to distal. There was a significant positive correlation between length of awns and dispersal ability, and awn removal significantly promoted seed germination. Germination was positively correlated with GA concentration and negatively correlated with ABA concentration, and the ABA: GA ratio was high in seeds with low germination/high dormancy. Thus, there was a continuous inverse–linear relationship between diaspore dispersal ability and degree of dormancy. This negative relationship between diaspore dispersal and degree of dormancy at different positions on a spike of Aegilops tauschii may facilitate seedling survival in space and time.