The size,distribution and germination requirements of the soil-stored seed-bank of Grevillea barklyana (Proteaceae)

Abstract Fire-triggered release from seed dormancy is a characteristic of many Australian plant species. We investigated aspects of the seed-bank dynamics and dormancy characteristics in seeds of Grevillea barklyana, an understorey shrub of coastal sclerophyll vegetation in the Jervis Bay Region on the south coast of New South Wales. We used two soil core sizes to compare the number and distribution of stored seeds in soil cores taken from underneath and outside the limits of plant canopies at three study sites. Core size did not affect the estimate of seed density. No seeds were found outside the existing canopies. Even in under-canopy samples, seed numbers were small. Mean seed densities were estimated as 10. 9, 14. 1 and 4. 3 seeds per for the three sites. A hierarchical series of laboratory experiments was used to test the germination response of both fresh and soil-stored seeds. Likewise, we attempted to simulate ‘natural’ disturbance conditions in a glasshouse experiment. Both laboratory and glasshouse experiments indicated polymorphism in germination behaviour. A constant proportion of seeds exhibited enforced dormancy, when moist at room temperature, while a smaller number of seeds showed either an induced dormancy or a non-seed-coat linked innate dormancy. The majority (75%) of seeds were innately dormant due to a hard seed-coat. This dormancy was broken when the seed-coat was damaged, for instance, by heat. The level of polymorphic germination behaviour will be dependent on the length of the inter-fire periods. We conclude that the expression of polymorphism within and between species across a range of environments and fire regimes is an important consideration for any further study attempting to assess the role of the seed-bank.     

Transgenic tobacco plants expressing the putative movement protein of tomato spotted wilt tospovirus exhibit aberrations in growth and appearance

Within the Bunyaviridae virus family, members of the genus Tospovirus are unique in their ability to infect plants. A characteristic genetic difference between tospoviruses and the animal-infecting members of this virus family is the occurrence of an additional gene, denoted NSM, located on the genomic M RNA segment. This gene has previously been implicated in the cell-to-cell movement of this virus during systemic infection. Transgenic tobacco plants have been obtained expressing the NSM protein of tomato spotted wilt virus (TSWV), the type member of the tospoviruses, from a constitutive promoter. Detectable amounts of the NSM protein could be observed in plants from nine different lines. The protein was only detectable in fractions enriched for cell wall material. More detailed immunogold labelling studies revealed specific association of NSM protein with plasmodesmata. Plants accumulating the NSM protein to detectable levels developed aberrations in growth, resulting in a significant reduction of size and accelerated senescence. In addition, these plants are restricted in their capacity to produce flowers. The results presented provide additional evidence that the NSM protein, by modifying plasmodesmata, represents the cell-to-cell movement function of tospoviruses. Furthermore, the phenotype of the NSM transgenic plants suggests involvement of the NSM gene product in TSWV symptom expression     

Floristic changes in shallow soft waters i n relation to underlying environmental factors

SUMMARY 1. Historical and recent data on the occurrence of macrophytes in twenty-eight lentic soft waters in The Netherlands are summarized. These waters were, and a few still are, characterized by a submerged vegetation of isoetid plants. Changes in the species composition of macrophytes are visualized by means of multivariate analysis and by shifts in species-spectra.
2. Ordination of the available data shows that the pH, alkalinity, acidity, contents of heavy metals, dissolved organic matter and some important salts and nutrients in water and interstitial water are strongly related to the recent distribution of aquatic plants in waters, which were originally of low alkalinity. In addition, the available inorganic carbon and the redox potential in the sediment are also important environmental parameters in explaining differences in aquatic vegetation.
3. The recorded changes in the macrophyte species composition can be attributed to the effects of acidification and eutrophication. The most important, overall change is a reduction of the number of species.
4. Hydrology proves to be important in controlling the sensitivity of a body of water for acidifying deposition.     

Multiplication and distribution of iris severe mosaic virus in secondarily-infected iris bulbs after stress induced by heat and wounding

In freshly-lifted iris bulbs infected with iris severe mosaic virus (ISMV), virus was not always detected in the basal plate and rarely in bulb scale tissue. After exposing the bulbs to stress (wounding or high-temperature treatment) the sensitivity of virus detection was enhanced. The improved detection of viral antigen after local stress (wounding) coincided with an increase of viral RNA synthesis. When general stress (high-temperature treatment) was applied, the virus could be reliably detected in the basal plate, and usually in vascular bundles and surrounding tissue. Virus was detected in the upper part of the bulb scale when such tissues were detached from the basal plate. Thus, virus must have been present in the scales in localised spots, albeit at a very low concentration, and multiplication is likely to be the main factor involved in the improved sensitivity of viral detection. The distribution of ISMV in the bulb after local or general stress treatment is discussed.     

The accumulation of genetic diversity within a canopy‐stored seed bank

Many plants regenerate after fire from a canopy‐stored seed bank, in which seed are housed in fire resistant confructescences (cones) that remain on maternal plants. This strategy would be favoured if plants accumulate a sufficiently large and genetically diverse seed bank during interfire intervals. We use a 16‐year demographic study and surveys of microsatellite variation to quantify and explain the rate of accumulation of genetic diversity within the canopy seed bank of the shrub Banksia spinulosa. Flowering and fruit set were highly variable. An initial sample in 1991 of 354 reproductively mature plants generated 426 cones over 16 years, of which only 55 cones from 40 maternal plants persisted until 2005. By genotyping seed from these 55 cones we demonstrated that genetic diversity accumulated rapidly within the seed bank. Resampling revealed that diversity was determined by the number, not the age, of cones. Cones were widely distributed among plants, outcrossing rates were high (mean t_m = 1.00 ± 0.04) and biparental inbreeding low. Adults displayed little evidence of isolation by distance and the genotypic diversity of seed cohorts was independent of the density of neighbouring potential sires. We therefore estimate that within at least 13 individual years the number of cones produced per year (14–63) would have contained 100% of the adult genetic diversity. We conclude that a highly outcrossed mating system and relatively widespread pollen dispersal ensure the rapid development of a genetically diverse and spatially and temporally homogeneous seed bank.     

Foliage‐age mixing within balsam fir increases the fitness of a generalist caterpillar

1. Manipulative field studies were carried out to evaluate the foliage age preference–performance relationship for an extreme generalist herbivore, the whitemarked tussock moth (Orygia leucostigma Smith) (Lepidoptera: Lymantriidae), within balsam fir [Abies balsamea (L.) Mill]. 2. Field surveys indicated that early instar caterpillars fed almost exclusively on young (i.e. current‐year) foliage, whereas late instars caterpillars fed on both young and mature (i.e. 1‐ and 2‐year‐old) foliage. 3. Survival of early instar caterpillars was highest in treatments where current‐year and/or 1‐year old foliage were available, but decreased significantly on older foliage. In contrast, late instar caterpillars had the highest survival when allowed to feed on all age classes of foliage, whereas potential fecundity was highest for late instars that fed on young foliage. 4. Overall, caterpillars had 32–65% higher fitness when able to feed on all rather than just one age class of foliage. 5. These results support both the ‘complementary diet' hypothesis, which states that dietary mixing of different‐aged foliage can increase nutrient uptake and/or dilute harmful secondary plant chemicals, and the ‘ontogeny’ hypothesis, which attributes changes in diet to changes in the nutritional needs and/or tolerance to plant defences of juvenile insects as they develop.     

Coscinoderma sporadense sp.n. from the Aegean Sea with comments on Coscinoderma confragosum (Porifera, Dictyoceratida)

Coscinoderma sporadense sp.n. is described from shallow waters in the North Aegean. This is the first record of a Coscinoderma species from the Mediterranean. The new species is compared to the deep water East Atlantic Coscinoderma confragosum Poléjaeff, 1884, and clear differences between them are established. The status of the genus Coscinoderma is discussed.     

Genetic characterization of hybridization between the New Zealand everlastings Helichrysum lanceolatum and Anaphalioides bellidioides (Asteraceae: Gnaphalieae)

Intergeneric hybridization between the endemic New Zealand species Helichrysum lanceolatum and Anaphalioides bellidioides (Asteraceae: Gnaphalieae) at two Banks Peninsula populations was investigated by DNA sequencing and amplified fragment length polymorphism fingerprinting. Crosses in both directions have contributed to the generation of the F1 hybrids, but in the study season hybridization was far more common with H. lanceolatum as the maternal parent. F1 hybrids have reduced, but considerable, fertility and seed collected from them includes back-crosses. Two hybrid plants sampled from the wild appear to be back-crosses to H. lanceolatum. Despite back-crossing, introgression was not demonstrated and is at most limited in scope. These results also corroborate important roles for small population size and rarity in the formation of hybrid lineages in New Zealand's everlastings.  © 2007 Landcare Research New Zealand Ltd. Journal compilation © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 89–98.     

Riverine landscape dynamics and ecological risk assessment

1. The aim of ecological risk assessments is to evaluate the likelihood that ecosystems are adversely affected by human‐induced disturbance that brings the ecosystem into a new dynamic equilibrium with a simpler structure and lower potential energy. The risk probability depends on the threshold capacity of the system (resistance) and on the capacity of the system to return to a state of equilibrium (resilience). 2. There are two complementary approaches to assessing ecological risks of riverine landscape dynamics. The reductionist approach aims at identifying risk to the ecosystem on the basis of accumulated data on simple stressor–effect relationships. The holistic approach aims at taking the whole ecosystem performance into account, which implies meso‐scale analysis. 3. Landscape patterns and their dynamics represent the physical framework of processes determining the ecosystem's equilibrium. Assessing risks of landscape dynamics to riverine ecosystems implies addressing complex interactions of system components (e.g. population dynamics and biogeochemical cycles) occurring at multiple scales of space and time. 4. One of the most important steps in ecological risk assessment is to establish clear assessment endpoints (e.g. vital ecosystem and landscape attributes). Their formulation must recognise that riverine ecosystems are dynamic, structurally complex and composed of both deterministic and stochastic components. 5. Remote sensing (geo)statistics and geographical information systems are primary tools for quantifying spatial and temporal components of riverine ecosystem and landscape attributes. 6. The difficulty to experiment at the riverine landscape level means that ecological risk management is heavily dependent on models. Current models are targeted towards simulating ecological risk at levels ranging from single species to habitats, food webs and meta‐populations to ecosystems and entire riverine landscapes, with some including socio‐economic considerations.