Small seed size increases the potential for dispersal of wetland plants by ducks

1. Long-distance dispersal (LDD) is important in plants of dynamic and ephemeral habitats. For plants of dynamic wetland habitats, waterfowl are generally considered to be important LDD vectors. However, in comparison to the internal (endozoochorous) dispersal of terrestrial plants by birds, endozoochorous dispersal of wetland plants by waterfowl has received little attention. We quantified the capacity for endozoochorous dispersal of wetland plants by waterfowl and identified the mechanisms underlying successful dispersal, by comparing the dispersal capacities of a large number of wetland plant species.

2. We selected 23 common plant species from dynamic wetland habitats and measured their seed characteristics. We fed seeds of all species to mallards (Anas platyrhynchos), a common and highly omnivorous duck species, and quantified seed gut survival, gut passage speed and subsequent germination. We then used a simple model to calculate seed dispersal distances.

3. In total 21 of the 23 species can be dispersed by mallards, with intact seed retrieval and subsequent successful germination of up to 32% of the ingested seeds. The species that pass fastest through the digestive tract of the mallards are retrieved in the greatest numbers (up to 54%) and germinate best (up to 87%). These are the species with the smallest seeds. Seed coat thickness plays only a minor role in determining intact passage through the mallard gut, but determines if ingestion enhances or reduces germination in comparison to control seeds.

4. Model calculations estimate that whereas the largest seeds can hardly be dispersed by mallards, most seeds can be dispersed up to 780 km, and the smallest seeds up to 3000 km, by mallards during migration.

5. Synthesis. This study demonstrates the mechanism underlying successful endozoochorous dispersal of wetland plant seeds by mallards: small seed size promotes rapid, and hence intact and viable, passage through the mallard gut. Mallards can disperse wetland plant seeds of all but the largest-seeded species successfully in relatively large numbers (up to 32% of ingested seeds) over long distances (up to thousands of kilometres) and are therefore important dispersal vectors.

Germination ecology and seed dispersal of a critically endangered plant: a case study of Pomaderris vacciniifolia (Round-leaf Pomaderris)

Change in ecosystem disturbance regimes from human land-use poses a worldwide problem for management of rare species. Two important types of disturbance influencing the persistence of species in Australian ecosystems are habitat fragmentation and fire. In this study, seed dispersal and the germination ecology of Pomaderris vacciniifolia-a critically endangered, rare endemic Australian shrub-were examined to identify likely influences of fire and fragmentation on the decline of populations. The response of seed germination to simulated effects of wildfire and canopy openings was investigated, as was the unaided dispersal capability of seeds from parent plants. A significant increase in germination rate was observed following 100°C heat treatment to seeds, while smoke and light exposure had little influence. Seed imbibition was strongly influenced by heat treatment. The findings indicate a likely positive post-fire germination response, with implications for recruitment success determined by moisture availability following fire. Unaided seed dispersal was limited, which partly explains the apparent decline of populations. Understanding disturbance requirements for threatened species, and subsequent management of landscapes for disturbance, will aid conservation of rare species throughout the world.

Effect of storage on the biochemical and processing quality of Adzuki Bean (Vigna angularis)

Storage of adzuki beans and other pulse grains causes biochemical and physical changes that affect the hydration properties of the beans. This affects the quality of products made from the beans such as the Japanese bean paste “ann.” Storage, particularly under unfavourable conditions, leads to the “hard shell” phenomenon, where beans fail to imbibe water when soaked and remain hard, and the “hard-to-cook” phenomenon where the seeds hydrate normally, but the cotyledon fails to hydrate and soften during cooking. The hard shell phenomenon is attributable to impermeability of the seed coat to water, which is due to biochemical changes in the seed coat, such as the formation of protein-tannin complexes, and biophysical changes such as reduction in size or closure of the straphiole aperture in the hilum area—the main area for water entry into the adzuki bean. The hard-to-cook phenomenon is due to changes in the cotyledon tissue, which include formation of insoluble pectinates, lignification of the cell wall and middle lamella, interaction of condensed tannins with proteins and starch, and changes to the structure and functionality of the cellular proteins and starch.

Seeding of single crystal superalloys--Role of seed melt-back on casting defects

Single crystal seeds of the nickel-base superalloy CMSX-4 have been partially melted in a temperature gradient and then quenched. Small islands of random orientation are observed throughout the melted-back semi-solid. These random orientations appear to be pinched-off secondary dendrite arms, but there is no evidence that they are transported ahead of the dendrite tips to nucleate stray grains during directional solidification.

Impact of saltmarsh disturbance on seed quality of Sarcocornia (Sarcocornia quinqueflora), a food plant of an endangered Australian parrot

The article presents a study which evaluates the impact of saltmarsh perturbation on seed quality of Sarcocornia which is a food for the endangered Orange-bellied parrot in Australia. It notes the significant impact of grazing on the energy and availability of Sarcocornia seeds in saltmarshes and indicates that graze-free saltmarshes with regular inundation provide the highest potential for Sarcocornia seed availability. Further, the substantial factor of soil characteristics and salinity of flood water and inundation on the seed production of Sarcocornia is also discussed.

Consequences of intraspecific seed-size variation in Sparganium emersum for dispersal by fish

1. The potential for seed dispersal by fish (ichthyochory) is likely to vary within aquatic plant species, depending on intraspecific variation in phenotypic seed traits.

2. We studied the effect of seed size variation within the unbranched burreed (Sparganium emersum) on the potential for internal dispersal by the common carp (Cyprinus carpio), by feeding them light (< 10 mg), medium (10–20 mg) and heavy ( > 20 mg) seeds, seed mass being positively related to seed size.

3. We hypothesized: (i) that ingestion, retention time, survival during gut passage and viability after gut passage of S. emersum seeds would be affected by seed size; and (ii) that this would translate into intraspecific variation in dispersal probability and dispersal distance among seed size categories.

4. Ingestion was negatively related to seed size, while survival during gut passage was positively related to seed size. Seed viability after gut passage was not affected by seed size. Since the negative effect of ingestion was counterbalanced by an equally strong but positive effect on seed survival, the probability of dispersal did not differ between the tested seed-size categories.

5. The time that seeds remained in the digestive tract of carp did not differ between seed sizes, suggesting equal potential dispersal distances for all seeds. Based on optimum swimming speeds of carp, ranging from 0·9 to 1·8 km h−1, maximum dispersal distances will most likely range from 13·5 to 27 km.

6. This study highlights the importance of studying all stages of the endozoochorous dispersal process in order to estimate the effect of a phenotypic seed trait on plant dispersal.

The effect of seed morphology on the potential dispersal of aquatic macrophytes by the common carp (Cyprinus carpio)

1. The potential for seed dispersal by fish (ichthyochory) will vary among aquatic plants because of differences in seed size and morphology.

2. To examine how seed morphology influences the probability of dispersal by the common carp (Cyprinus carpio), we studied seed ingestion, retention time and subsequent egestion and germination of seeds of Sparganium emersum and Sagittaria sagittifolia, two aquatic plant species with similar sized but morphologically different seeds.

3. We compared dispersal probabilities between the two plant species, in which the probability of dispersal is assumed to be a function of the probabilities of seed ingestion, egestion and germination, and the dispersal distance is assumed to be a function of seed egestion rate over time.

4. We found that, although the soft seeds of S. sagittifolia had an approximately 1.5 times higher probability of being ingested by the carp than the hard seeds of S. emersum (83.15% ± 1.8% versus 56.16% ± 2.7%, respectively), the latter had an almost twofold higher probability of surviving the passage through the digestive tract (38.58% ± 2.7% versus 20.97% ± 1.5%, respectively). Patterns of seed egestion over time did not differ between the two plant species, despite the difference in seed morphology. Gut passage had a different effect on seed germination between plant species. Compared with non-ingested controls, seeds of S. emersum showed a 12.6% increase in germination and a 2.1 day acceleration in germination rate, whereas seeds of S. sagittifolia displayed a 47.3% decrease and 5.1 day delay, respectively.

5. Our results suggest that seed morphology affects the dispersal probability and postdispersal establishment, but not the dispersal distance, of aquatic plants that are dispersed by fish.