Academic literature on the topic 'Diuris orchids'

Twenty-three orchid species were recorded in Alcoa's permanent vegetation-monitoring plots in unmined and rehabilitated jarrah forest. Of these, 22 were identified in the unmined jarrah forest and 20 were recorded in rehabilitated areas of between 1 and 31 years old. Three species (Cyrtostylis ovata, Lyperanthus serratus and Prasophyllum elatum) were only recorded in the unmined forest and one species was only recorded in rehabilitated areas (Diuris carinata). The overall density of native orchids in the forest was 13 755 plants ha–1, 10 times greater than the density in rehabilitated areas (1381 plants ha–1). The most abundant species in the forest were Cyrtostylis robusta, Caladenia flava, Pterostylis nana and Thelymitra crinita, all with densities greater than 1000 plants ha–1. The most abundant species in the rehabilitated areas were Microtis media, Disa bracteata (an introduced species), Caladenia flava, Pterostylis nana, Diuris longifolia and Pterostylis vittata, all with densities greater than 60 plants ha–1. In rehabilitation older than 10 years, the density of orchids increased to 2685 plants ha–1. Burning in rehabilitated areas resulted in large increases in orchid densities. It is believed that orchid colonisation of rehabilitated bauxite mines is dependent on symbiotic mycorrhiza, which are in turn dependent on development of an organic litter component in the soil.

Floral deception has been observed in several genera in angiosperms, but is most common in the Orchidaceae. Pollination mechanisms in food deceptive plants are often difficult to assess, as visitation frequency by insects requires numerous hours of field observations to ascertain. Here, for the first time, we describe in detail and validate a simple and effective method that extends previous approaches to increase the effectiveness of pollination studies of food deceptive orchids. We used an orchid of southwest Australia, Diuris brumalis (Orchidaceae), that visually mimics model plants belonging to the genus Daviesia (Faboideae). Arrays of orchid flowers were placed and moved systematically in proximity to model plants, resulting in rapid attraction of the pollinators of D. brumalis. We compared pollinaria removal (as an indicator of pollination success) in naturally growing orchids with pollinaria removal in arrays of orchid flowers in the same sites. We showed that the proposed method greatly enhances pollinator attractiveness in food deceptive systems with very low pollination rates, and we compared its efficiency with other similar methods. The approach can be used for observing pollinator behavioural patterns and confirming effective pollinators for food deceptive species with low insect visitation rates.

The establishment of five species of temperate terrestrial orchids (Caladenia arenicola Hopper & A.P.Brown, Diuris magnifica D.L.Jones, D. micrantha D.L.Jones, Pterostylis sanginea D.LJones & M.A.Clem. and Thelymitra manginiorum ms) in natural habitat through in situ seed sowing, or by planting of seedlings and dormant tubers, was evaluated. Seed of the Western Australian temperate terrestrial taxa, Caladenia arenicola and Pterostylis sanguinea germinated best when sown into soil inoculated with mycorrhizal fungi at field sites but failed to develop the tubers necessary for surviving summer dormancy. However, seedling survival improved when actively growing symbiotic seedlings were transferred to natural habitat during the growing season. Caladenia arenicola and P. sanguinea seedlings survived the initial transfer to field sites but only P. sanguinea survived into the second growing season. Highest survival was obtained by translocating dormant tubers of C. arenicola and Diuris magnifica, with D. magnifica persisting at the site 5 years after translocation. However, outplanted C. arenicola survived for only 2 years. In another trial, where seedlings and dormant tubers of a rare orchid Thelymitra manginiorum were translocated into eucalypt woodland, 18% persisted after 5 years. The rare orchid D. micrantha exhibited the highest survival rates, with greater than 80% of tubers surviving 5 years after transfer of mature dormant tubers to field sites. This study highlights the benefit of using optimised methods for seedling production by symbiotic germination and nursery growth to produce advanced seedlings or dormant tubers to maximise the survival of translocated plants. It also demonstrates the need to consider different strategies when dealing with individual species.

Ex situ conservation of threatened terrestrial orchids requires the simultaneous conservation of their mycorrhizal associations. A method for encapsulating both seed and fungi in alginate beads (known as encapsulation–dehydration) was applied to the storage and propagation of two endangered orchid species in NSW, Australia—Pterostylis saxicola D.L.Jones & M.A.Clem. and Diuris arenaria D.L.Jones. We tested the effect of storage duration and temperature on fungal recovery and germination potential in vitro, and recorded survival for seedlings subsequently transferred to potting mix. Storage at 23°C significantly reduced fungal recovery and germination for both species after only 3 months (P < 0.05), whereas storage at 4°C significantly reduced fungal recovery for P. saxicola after 6 months (P < 0.05). Storage for 6 months at −18 and −196°C had no significant effect on the fungal recovery and germination percentages of either species. All beads transferred directly from in vitro culture to potting mix resulted in the establishment of at least one seedling, and production of a healthy tuberoid, when transferred near the commencement of the natural growing season. The encapsulation–dehydration method may have a practical application for use in ex situ conservation of other terrestrial orchids, as well as their mycorrhizal fungi.

Seeds of two Australian terrestrial orchid species (Caladenia latifolia R.Br. and Diuris magnifica D. Jones) were germinated in a potting mix of Allocasuarina fraseriana (Miq.) L. Johnson leaf mulch and perlite (1:1). The potting mix was irradiated (7 Gy for 14 hours), steam pasteurized (70C for 30 minutes) or nontreated, and inoculated with the appropriate mycorrhizal fungus for each species, a sterile red fungus (SRF), or both. Protocorm formation and green shoots were evident at 8 and 10 weeks, respectively, after seed sowing. The highest mean number of seedlings was 84 for C. latifolia and 234 for D. magnifica per 270-ml container in pasteurized potting mix inoculated with mycorrhizal fungi and SRF. Shoots were longest after 20 weeks (28 mm for C. latifolia and 52 mm for D. magnifica, respectively) in pasteurized potting mix inoculated with mycorrhizal fungi only. Germination was absent in control treatments without mycorrhizal fungi; with SRF only; or in nonsterile potting mix with mycorrhizal fungi, SRF, or both.

Determining the seed quality and germination requirements for threatened orchid species in storage is vital for future conservation efforts. Seeds of many Australian terrestrial orchid species are held in conservation collections around the country, but few have been germinated in vitro, fuelling concerns over their long-term viability. This study tested three methods of assessing orchid seed quality; asymbiotic germination was compared with vital staining using triphenyltetrazolium chloride or fluorescein diacetate. Six culture media were examined for efficacy in promoting asymbiotic seed germination of four Australian terrestrial orchid species (Pterostylis nutans, Microtis arenaria, Thelymitra pauciflora and Prasophyllum pruinosum). Germination occurred on all media but germination rates were consistently highest on BM1 and development was most advanced on BM1, P723 and Malmgren media. Subsequent trials tested the efficacy of BM1 for asymbiotic germination of additional genera (Caladenia, Calochilus and Diuris), several congeneric species, and two species collected from several different provenances within each of their ranges. The results indicate that asymbiotic germination on BM1 medium is an effective technique for testing the performance of Australian terrestrial orchid seeds. The efficacy of vital stains to determine seed viability, however, remains uncertain, as significant disagreement between degree of staining and germinability was observed for some species.

The impact of seed drying, seed storage and development of testing procedures for seed viability assessment was undertaken for a selection of common taxa with congeners that are rare and endangered (Caladenia, Diuris, Pterostylisand Thelymitra). Freshly collected seed showed significantly lower levels of germination compared with seed that had been subjected to drying over silica gel for 24 h. Seed dried over silica gel for 24 h and plunged into liquid nitrogen exhibited a further increase in germination levels. Germination of seed stored at 4, 18 or 22˚C for 1 year was substantially higher than freshly collected seed (4 weeks after dehiscence), but germination was highest overall after storage of dried seed in liquid nitrogen (–196˚C). Mycorrhizal fungi that promote the germination and growth of plants were also successfully preserved in liquid nitrogen. The use of cryoprotectants on fungal isolates had no observable deleterious effects on fungal regeneration. Histochemical staining procedures (tetrazolium, fluorescein diacetate and Evans blue) substantially overestimated seed viability, relative to symbiotic seed germination, for most seed treatments indicating a need for re-evaluation of the effectiveness of staining procedures for testing viability. The implications of the long-term ex situ storage of orchid seed and fungal symbionts for the conservation of endangered orchids is discussed.

Orchids have high rates of speciation and extinction, and are over-represented on threatened species lists. Reintroductions are being used with increasing frequency as an important tool for threatened orchid recovery. The ultimate aim of these reintroductions is to create a self-sustaining population that will reduce the risk of extinction for the species. In this case study, we test the hypotheses that state transition, annual survival, and seed production rates in a reintroduced population were equivalent to those in the wild population. These hypotheses were tested using long-term demographic monitoring datasets from a wild and a reintroduced population of Diuris fragrantissima, and analysed using Bayesian multistate capture–recapture and multinomial models. The results showed that emergent plants at the reintroduction site were more likely to transition to vegetative or unobserved states, and less likely to flower in the following year, than those at the wild site. This resulted in a strong trend through time away from emergent life states at the reintroduction site. The estimated annual survival rate was &gt;90% at the wild site, and &lt;80% in five of the seven years at the reintroduction site. Flowering was the most frequently recorded life state at the wild site. The fate of an individual flower was not affected by site (wild or reintroduction), but an increase in rainfall increased the probability that a flower would set seed and decreased the probability that it would be browsed. The reintroduction has failed to produce a stable, sustainable, long-term population, but it has been valuable in providing information that will inform the development and improvement of future D. fragrantissima reintroductions. Improving our knowledge in these areas should increase the chances of future D. fragrantissima reintroductions being assessed as a success.

This research aimed to improve the success of soil transfer of terrestrial orchid seedlings after symbiotic germination in the laboratory. Three native Western Australian terrestrial orchids (Caladenia arenicola Hopper & A.P.Brown, Diuris magnifica D.L.Jones and Thelymitra crinita Lindley) were used in this study. The key to improved seedling survival on transfer to soil was found to be the use of an intermediate stage between the Petri dish and soil where larger seedlings were grown in an axenic environment with controlled humidity. There was no apparent benefit of pre-inoculating potting medium with appropriate strains of mycorrhizal fungi for subsequent growth of symbiotic seedlings under glasshouse conditions. Initial survival of seedlings in the glasshouse was high. However, some seedlings failed to produce tubers (from modified roots or droppers) necessary for plant survival through the summer dormancy period, and this caused survival to decrease to 40–60% of the glasshouse-grown seedlings in the first year. The initiation of tubers on droppers by C. arenicola was inversely correlated with leaf size, with smaller plants more likely to form tubers. This suggests that leaves and tubers were competing for resources. However, larger seedlings that did tuberise had larger tubers that were more likely to survive summer dormancy. There was no correlation between leaf size and root tuber size in D. magnifica, but the number of tubers produced was greatest in larger plants. As with C. arenicola, plants of D. magnifica and T. crinita with larger tubers were more likely to survive summer dormancy. Methods developed in this study enable the production of both actively growing symbiotic seedlings and dormant tubers which improve the success of translocation of laboratory-grown terrestrial orchids to field sites.

Phenology is the study of recurring life-cycle events that are initiated and driven by environmental factors, such as the response of flowering time to the prevailing climate. Ongoing climate change is thus expected to impact on the flowering time of plant populations with consequences for reproductive success in the short term and their survival in the long term, along with potentially widespread repercussions for associated ecological health and function. Tracking phenological shifts in response to past climate variability provides a benchmark or reference point for gauging future impacts. The introductory chapter of this thesis presents a review of the literature as it relates to my research documented in the following three chapters. Chapter 2 provides an exploration of the impacts of climate on the flowering phenology of the South Australian endemic Diuris orchid genus. A statistical analysis, trialling the suitability of Generalized Additive Models for Location, Scale and Shape (GAMLSS) for modelling of a long-term, historical dataset showed a significant curvilinear trend, with peak flowering advancing over time. This investigation was extended to determine the main and interactive effects of temperature and rainfall as specific drivers of Diuris flowering phenology (Chapter 3). A highly significant flowering response to seasonal temperatures and rainfall was identified, with shifts to earlier flowering in warmer and drier seasons expected under climate change scenarios. Chapter 4 comprises various analyses of a 44-year replicate data set of 112 Pyrus (pear) trees growing at the University of Adelaide Waite Arboretum. This aspect of my research provided a unique opportunity to study the phenological responses of a non-native genus at the species and individual levels, when subjected to identical environmental conditions. A general response to minimum temperature was, on occasions, overridden by an early flowering response initiated by drought-breaking rains. This study also allowed a comparison to be made between Pyrus phenology in the northern and southern hemispheres, and an insight into the potential economic impacts for South Australian horticulture. Evolutionary implications for all study species arising from climatically-induced phenological shifts are outlined in Chapter 5, including a consideration of the likelihood that the rate of evolutionary change will be sufficient to keep pace with predicted climate change scenarios. Findings from these investigations are then considered in relation to the selection of bioclimatic indicators. In this sixth chapter, I challenge the validity of many assertions and assumptions presented in the literature. This thesis concludes that the stresses of ongoing climate change will have a selective impact on the reproductive fitness of flowering plants growing in South Australia. Outcomes will vary dependent upon individual populations and species, geographic location and evolutionary history.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2013