Australian Journal of Botany最新文献

The first general overview of mycorrhizal functional groups associated with the flora of the Queensland Sunshine Coast heathlands, a community of low phylogenetic diversity, is provided in this Short Communication. Broad proportions of plant species associated with mycorrhizal and non-mycorrhizal functional groups in the heathlands were compared with those in the surrounding rainforest flora, and across the heath strata. This overview suggests that a greater diversity of mycorrhizal strategies and an increased number of plant genera with non-mycorrhizal associations are found in the heathlands, with proportions varying among the strata. These associations may be facilitating the coexistence of plant species and increasing phylogenetic dispersion.

The failure of the Fundão dam devastated a large area of the Atlantic Forest, causing damage to and loss of riparian forests. Considering all the ecological roles of a terrestrial and freshwater community, it is necessary to understand the functioning of riparian forests and their regenerative potential, which will be decisive in selecting actions to restore these ecosystems, especially Atlantic Forest remnants.

We evaluated the flora and structure of the regenerating stratum in three riparian vegetation remnants along the Rio Doce basin to support the propagation and restoration of the affected environments.

Plots of 5 m × 5 m were made in each area, totalling 77 sampling units. In these plots, all woody individuals with a diameter at soil height (DSH) of at least ≥1 cm and diameter at breast height (1.3 m from the soil) of at least <5 cm were marked, measured (in height and DSH), sampled and identified.

A total of 275 species distributed in 47 families were sampled, with Fabaceae the most diverse family and Siparuna guianensis Aubl. the most abundant species. Variation in β diversity was significant, and composition analysis showed that plots of each area tended to cluster. Principal component analysis and linear models showed that the edaphic parameters were not related to the richness and abundance of species in the sampled areas.

The areas sampled here serve as a reference for the restoration of impacted areas.

This study represents an important step towards knowing the species in reference areas for an active and efficient restoration in impacted areas.

Knowledge of the reproductive biology of plants is fundamental for conservation, especially of the ones with a limited distribution.

The sexual reproduction of the small-ranged Passiflora chrysophylla Chod. was studied.

Controlled pollinations were performed to assess the breeding system, whereas floral traits and visitors (identity, frequency, activity on the flowers, dimensions and pollen load) were analysed to assess the pollination mechanism.

Self-compatibility was partial. Anthesis was matinal. The odour emitted by the corona was sweet, whereas the odour emitted by the persistent sepals and bracts was similar to that of the leaves. Contrasting concentric circular reward guides were present in the visible and UV spectra. Nectar concentration was high, the volume increased throughout anthesis and, if removed, nectar was replenished only once during the flower lifespan. Style movements towards the anthers determined male and hermaphroditic phases in most of the flowers; in a few flowers (smaller, scented and nectarless), styles remained apart from the anthers, thus constituting a functionally andromonecious and deceptive automimicry system. The bees Ptiloglossa sp., Thygater analis and Xylocopa augusti acted as pollinators, whereas ants, butterflies and beetles were nectar or pollen thieves and florivores.

P. chrysophylla is melittophilous and pollinators increase reproductive success.

Pollination biology of P. chrysophylla, reported for the first time, would contribute to conservation management of this species with restricted distribution.

Themeda triandra (Forssk.) is a tussock grass of international importance for its keystone role in grassy ecosystems and, hence, is often a focus for seed production, research and ecological restoration. However, these applications can be challenged by its seed biology, including seed dormancy and the variability of seed traits among populations. The literature on these topics has not been well synthesised. To address this, we reviewed the relevant literature for Themeda triandra seed and found that seed quality is often poor but highly variable, and there are no current quality-assurance standards. Seed characteristics such as weight, awn length and desiccation tolerance can vary with seed ploidy (i.e. the number of chromosome sets). Germination rates of fresh Themeda triandra seed can be as low as 5%, which may be due to seed dormancy. Dormancy varies among populations and with seasonal conditions, and a period of dry storage at room temperature for 8–10 months may be needed before it will reach its full germination potential. No single treatment is effective in overcoming dormancy across all populations. The application of gibberellic acid can increase germination by ~30% in some populations. Although plant-derived smoke products can be effective, they also lack standardisation. Other treatments including the application of heat, or wet–dry cycling warrant further investigation. We recommend the standardisation of Themeda triandra seed testing and labelling, which would allow end users to assess value for money when purchasing seed commercially.

A combination of industrial activities, agricultural practices, and poor urban planning has led to soil and plant contamination throughout the world. Heavy metal stress responses in plants have been demonstrated in various studies, but it remains unclear how heavy metals affect tree germination and initial establishment.

With a focus on species selection for phytoremediation programs in areas with copper (Cu) soil contamination, we aimed to evaluate seed germination, initial growth, and carbohydrate and protein metabolism of seedlings of Hymenaea courbaril, Stryphnodendron pulcherrimum, and Hevea brasiliensis subjected to normal and high (500 mg kg⁻¹) concentrations of Cu. We hypothesised that there are differences in the Cu effects and plant responses on germination, initial growth, and the metabolism of seedlings from different Amazon tree species.

The germination experiment was conducted with seeds of the tree forest species in the absence or presence of Cu. After germination-parameter analyses, biometric variables, soluble sugars, starch, and proteins were measured.

In the presence of Cu, the germination traits, and morphological variables of H. brasiliensis were changed, whereas Cu did not strongly affect the other species. All species showed a high metabolic adjustment capacity, with little impact on the metabolism of carbon and nitrogen-related compounds in seeds. Overall, it was therefore possible to verify that S. pulcherrimum and H. courbaril were able to tolerate Cu because of their good performance in the germination stage and maintenance of essential metabolites, whereas H. brasiliensis was more sensitive to the presence of this heavy metal.

Our results provided insights into the ability of tree species to cope with Cu stress and the hypothesis has been confirmed to interspecific differential tolerance.

Amazonian tree species show valuable potential for improving phytoremediation programs with a focus on soil contamination by Cu.

The South American grass Nassella trichotoma (serrated tussock) is widely distributed in central Argentina and one of the most damaging invasive species in Australia, New Zealand, and South Africa. In Australia, it is a weed of national significance.

Our aim was to characterise the fungi able to colonise N. trichotoma seeds buried at a site in south-western Buenos Aires province, Argentina, and measure their impact on seed survival and germination.

We tested the germination of healthy seeds at the beginning of the experiment (control). We buried 10 mesh bags containing 100 disinfected N. trichotoma seeds each, during 3 months in spring and autumn. At the end of each experiment, the contents of five of the bags were counted and classified as germinated, healthy, damaged, or disintegrated. Germination tests were then conducted with seeds of the latter three categories. The remaining seeds were used for recording fungal signs/symptoms, and the isolation of fungi.

We identified and described a diverse group of fungi associated with the seeds and a seasonal variation in the specific composition. Seeds showing fungal signs and/or symptoms germinated less than the control.

This is the first study on fungi associated with seeds of this species in the native range, which can affect their survival and longevity.

It is expected that studies on the seed microbiome may help us understand the differences in behaviour of the plant between ranges, and test the enemy-release hypothesis.

Australia has numerous threatened species of terrestrial orchid, with a particularly high incidence of rarity in the genus Prasophyllum R.Br. Although there has been research on mycorrhizal associations and propagation, little is known about the reproductive ecology of threatened Prasophyllum. Understanding which animals are responsible for pollination and the impact of herbivores on reproduction may inform conservation actions.

For the nationally Critically Endangered Prasophyllum innubum, we aimed to determine the pollinator species, test for self-pollination, quantify levels of reproductive success and herbivory, and identify herbivores.

Pollinator observations were undertaken at wild populations of P. innubum, whereas an experiment testing for self-pollination was undertaken in shadehouse conditions. We quantified reproductive success and herbivory at two populations and attempted to identify herbivores using game cameras.

Pollination occurred via three species of bee and a sphecid wasp, all of which attempted feeding on floral nectar. Fruit set averaged 72–84% at wild sites, whereas only 6% of flowers set fruit via self-pollination when insects were excluded. Just 4% of inflorescences were completely consumed by herbivores, and no herbivory was captured on camera.

P. innubum has a generalist rewarding pollination system that confers high levels of reproductive success, with herbivory having little impact on reproduction.

Pollinator availability is unlikely to restrict conservation translocation site selection of P. innubum because of a generalist pollination system. If herbivores are a threat for this species, it is likely to be through alteration of habitat rather than direct grazing.

The Cerrado stricto sensu is a physiognomy under a seasonal climate of Cerrado vegetation, a Neotropical savanna, showing insignificant light restriction for adult tree species with branches above the herbaceous stratum.

We capture shoot and foliage production in 15 Cerrado tree species with distinct leaf phenology, following marked buds to investigate the strategies of air space acquisition and the influence of monthly air temperature and rainfall over a growing season.

Five buds were marked in every five individuals per species during the 2016 dry season in deciduous, semideciduous, and evergreen trees, encompassing five species per leaf habit.

Deciduous trees had plagiotropic shoots with 35° of inclination, whereas semideciduous and evergreen species had orthotropic (60°) shoots. Evergreen Miconia albicans was the single study species with a second-order shoot, and apical meristem death occurred only in deciduous trees. Two deciduous trees (Caryocar brasiliense and Diospyros hispida) and semideciduous Eriotheca gracilipes increased leaf number per shoot with monthly total precipitation. D. hispida and E. gracilipes also showed a positive correlation among shoot length, monthly air temperature, and monthly precipitation.

Only 3 of the 15 studied species showed a correlation between shoot or foliage production and monthly climate variables during the wet growing season. Deciduous trees avoid foliage self-shading, producing slanting short shoots with leaf flush preceding heavy rains, facilitating rapid branch and foliage formation to offset the leaf-free period quickly. Conversely, evergreen trees, characterised by orthotropic long shoots and slower vegetative growth, rely on foliage self-shading to sustain leaf persistence during seasonal drought. Semideciduous species commonly exhibited shoot- and leaf-trait variables such as those observed, on average, in deciduous or evergreen trees, resulting in a continuous spectrum of trait variations among the leaf phenological groups.

Each growth strategy in every leaf habit showed a particular air space acquisition across seasons, usually keeping shoot and foliage production independent of monthly climate variability in the wet growing season. These findings emphasised the significance of characterising the leaf phenological assemblages of the vast Cerrado woody flora as inherent functional groups in a continuum of crown trait variation, enabling the identification of strategies to capture, use, and store resources in each tree group.

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.

Phytoliths constitute an important source of silicon in terrestrial and aquatic ecosystems. Schoenoplectus californicus (C.A.Mey.) Soják (Cyperaceae) is an important phytolith producer.

We investigated the spatio-temporal variation in phytolith content of S. californicus in shallow lakes of the Pampean region, considering biomass and its relation to soil silicon content and lignin content.

Calcination techniques were applied to quantify phytoliths. The biomass was estimated by destructive methods. Soil silicon concentration was determined through ultraviolet–visible spectrophotometry by means of the silicomolybdate method. For lignin determination, a fibre analyser and sulfuric acid were used.

No significant differences were observed in the spatio-temporal analysis. There were no differences in the biomass estimation and in the phytolith per m² contribution. Regarding soil silicon content, when the concentration was low, the phytolith production was low. Lignin content remained constant between sites. No correlation was observed between phytolith and lignin content.

S. californicus is an accumulator of amorphous silica, generating a constant quantity of phytoliths over the years and between sites. The variation in some environmental conditions does not seem to be enough to be reflected in plant silica production. No relation between lignin and silica was found, perhaps due to their different roles in plant structure.

The inclusion of other wetlands with more contrasting conditions may reveal the environmental constraints for the amorphous silica production. This study shows the importance of this community as a silicon source, and the implications of its displacement by other communities or urban development.