bluuebunny/crossref_metadata_2025 huggingface dataset:
Reaction dynamics following electron capture of chlorofluorocarbon adsorbed on water cluster: A direct density functional theory molecular dynamics study
Authors: Tachikawa Hiroto , Abe Shigeaki
Published: May 2007

The electron capture dynamics of halocarbon and its water complex have been investigated by means of the full dimensional direct density functional theory molecular dynamics method in order to shed light on the mechanism of electron capture of a halocarbon adsorbed on the ice surface. The CF2Cl2 molecule and a cyclic water trimer (H2O)3 were used as halocarbon and water cluster, respectively. The dynamics calculation of CF2Cl2 showed that both C–Cl bonds are largely elongated after the electron capture, while one of the Cl atoms is dissociated from CF2Cl2− as a Cl− ion. Almost all total available energy was transferred into the internal modes of the parent CF2Cl radical on the product state, while the relative translational energy of Cl− was significantly low due to the elongation of two C–Cl bonds. In the case of a halocarbon-water cluster system, the geometry optimization of neutral complex CF2Cl2(H2O)3 showed that one of the Cl atoms interacts with n orbital of water molecules of trimer and the other Cl atom existed as a dangling Cl atom. After the electron capture, only one C–Cl bond (dangling Cl atom) was rapidly elongated, whereas the other C–Cl bond is silent during the reaction. The dangling Cl atom was directly dissociated from CF2Cl2−(H2O)3 as Cl−. The fast Cl− ion was generated from CF2Cl2−(H2O)3 on the water cluster. The mechanism of the electron capture of halocarbon on water ice was discussed on the basis of the theoretical results.
Phase diagram of Gaussian-core nematics
Authors: Prestipino Santi , Saija Franz
Published: May 2007

The authors study a simple model of a nematic liquid crystal made of parallel ellipsoidal particles interacting via a repulsive Gaussian law. After identifying the relevant solid phases of the system through a careful zero-temperature scrutiny of as many as eleven candidate crystal structures, they determine the melting temperature for various pressure values, also with the help of exact free energy calculations. Among the prominent features of this model are pressure-driven reentrant melting and the stabilization of a columnar phase for intermediate temperatures.
Correlations between designability and various structural characteristics of protein lattice models
Authors: Yang Jian-Yi , Yu Zu-Guo , Anh Vo
Published: May 2007

Using six kinds of lattice types (4×4, 5×5, and 6×6 square lattices; 3×3×3 cubic lattice; and 2+3+4+3+2 and 4+5+6+5+4 triangular lattices), three different size alphabets (HP, HNUP, and 20 letters), and two energy functions, the designability of protein structures is calculated based on random samplings of structures and common biased sampling (CBS) of protein sequence space. Then three quantities stability (average energy gap), foldability, and partnum of the structure, which are defined to elucidate the designability, are calculated. The authors find that whatever the type of lattice, alphabet size, and energy function used, there will be an emergence of highly designable (preferred) structure. For all cases considered, the local interactions reduce degeneracy and make the designability higher. The designability is sensitive to the lattice type, alphabet size, energy function, and sampling method of the sequence space. Compared with the random sampling method, both the CBS and the Metropolis Monte Carlo sampling methods make the designability higher. The correlation coefficients between the designability, stability, and foldability are mostly larger than 0.5, which demonstrate that they have strong correlation relationship. But the correlation relationship between the designability and the partnum is not so strong because the partnum is independent of the energy. The results are useful in practical use of the designability principle, such as to predict the protein tertiary structure.
Reversible, high-voltage square-wave pulse generator for triggering spark gaps
Authors: Robledo-Martinez A. , Vega R. , Cuellar L. E. , Ruiz-Meza A. , Guzmán E.
Published: May 2007

A design is presented for a reversible, square-pulse generator that employs coaxial cables for charge storage and pulse formation and a thyratron as the switch. The generator has a nominal output voltage of 5–30kV and a pulse duration determined by the cable’s physical length. Two variations are presented: (1) a single-stage one consisting of cable that is charged via its shield on one end and discharged with a thyratron on the opposite end and (2) a two-stage one having an inverting circuit that uses a coaxial cable to reverse the polarity of the pulse. The generator operates with “flying shields,” i.e., high-voltage pulses also propagate on the outside of the cables; this calls for a dedicated insulation that avoids breakdown between sections of the cable’s shield. The rise time obtained is mostly dictated by the switching time of the thyratron; with the one we used in the tests, rise times in the range of 30–40ns were obtained. We present the results obtained in the implementation of the generators as well as its application to fire a large Marx generator.
Synthesis of the ferroelectric solid solution, Pb(Zr1−xTix)O3 on a single substrate using a modified molecular beam epitaxy technique
Authors: Anderson P. S. , Guerin S. , Hayden B. E. , Khan M. A. , Bell A. J. , Han Y. , Pasha M. , Whittle K. R. , Reaney I. M.
Published: May 2007

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1−xTix)O3 (PZT) on single Pt∕Ti∕SiO2∕Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral to tetragonal symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary at Zr:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis. Results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery.
Electrode influence on the transport through SrRuO3∕Cr-doped SrZrO3/metal junctions
Authors: Lee Hwan-Soo , Bain James A. , Choi Sukwon , Salvador Paul A.
Published: May 2007

The authors have investigated the charge transport properties across heterostructures built from a SrRuO3 bottom electrode, a Cr-doped SrZrO3 perovskite film, and different top electrode metals (Pt, Cu, Ag, Cr, Mg, and SrRuO3). The resistances of such junctions were dependent on the top metal and ranging between 1 and 1000kΩ. The observed I-V curves were modeled with the equation I(V)=aV+bV2, where the variation of a with metal type was related to the work function while the variation of b was related to the oxygen affinity of the metal, consistent with space charge limited conduction through a defected interface.
Ferro- and piezoelectric properties of vinylidene fluoride oligomer thin film fabricated on flexible polymer film
Authors: Matsumoto Arifumi , Horie Satoshi , Yamada Hirofumi , Matsushige Kazumi , Kuwajima Shuichiro , Ishida Kenji
Published: May 2007

The ferro- and piezoelectric properties of vinylidene fluoride oligomer thin films fabricated on flexible polymer substrates were investigated under mechanical bending. Rectangular electric-displacement–electric-field hysteresis curves were observed for a polyimide substrate, and the remanent polarization and coercive electric field were unaffected on one-dimensional bending with a radius of curvature down to 10mm. The piezoelectric charge generated by the bending and restoring process was measured and found to be dependent on the radius of curvature. These results indicate the possibility using the vinylidene fluoride oligomer in the construction of both flexible nonvolatile memories and curvature sensors.
a
-
Si
:
H
∕
c
-
Si
heterointerface formation and epitaxial growth studied by real time optical probes
Authors: Gielis J. J. H. , van den Oever P. J. , van de Sanden M. C. M. , Kessels W. M. M.
Published: May 2007

The deposition of amorphous and epitaxial silicon thin films on H-terminated Si(100) has been studied in real time by the simultaneous application of spectroscopic ellipsometry, attenuated total reflection infrared spectroscopy, and optical second-harmonic generation. The morphology development of the films could be monitored nonintrusively in terms of critical point resonances and H bonding resolving the abruptness of the film-substrate interface and providing a clear distinction between direct heterointerface formation, nanometer-level epitaxial growth, and epitaxial breakdown.
Femtosecond laser stimulation of electrical discharges in submicron and nanoscale gaps
Authors: Chen J. , Farson D. F. , Rokhlin S. I.
Published: May 2007

Electrical characteristics of current-controlled discharges stimulated by femtosecond laser pulses in nanoscale gaps between sharpened metal tips and gold film substrates were studied. Pulse intensity of 5.6×1011W∕cm2 reliably triggered transient discharges in 500nm gaps. For gaps shorter than a threshold value, discharge stimulation probability was high and independent of applied potentials. At lower laser intensity, the discharge stimulation probability was also lower and depended on applied potential. It is suggested that the laser stimulated microdischarge mechanism observed in these experiments is associated with asperity breakdown by femtosecond laser ablation and field emission, resulting in release of charge carriers.
Efficiency enhancement and voltage reduction in white organic light-emitting devices
Authors: Lai S. L. , Chan M. Y. , Fung M. K. , Lee C. S. , Lee S. T.
Published: May 2007

High-efficiency and low operating voltage fluorescent white organic light-emitting devices (WOLEDs) have been realized by doping either 4,7-diphenyl-1,10-phenanthroline (BPhen) or N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) into the blue light-emissive layer. Devices doped with BPhen (or NPB) exhibited a maximum power efficiency of 8.7lm∕W (7.6lm∕W), about 74% higher than that of the reference device (5.0lm∕W). Such performance improvement is ascribed to the incorporation of a better electron-transporting layer and an improved carrier transport through the emissive layer by mixing with the higher drift mobility materials. It provides a simple and general means to improve the power efficiency of WOLED.
Barrier composition dependence of the internal electric field in ZnO∕Zn1−xMgxO quantum wells
Authors: Bretagnon T. , Lefebvre P. , Guillet T. , Taliercio T. , Gil B. , Morhain C.
Published: May 2007

Time-integrated photoluminescence experiments are used to study the excitonic optical recombinations in wurtzite ZnO∕Zn1−xMgxO single quantum wells of varying widths and magnesium compositions. By comparing experimental results with a variational calculation of excitonic energies, the authors determine the magnitude of the built-in electric field that is induced by both spontaneous and piezoelectric polarizations. It is found that the electric field varies linearly with magnesium composition. By taking into consideration the well-known distribution of electric field among the barrier and the well layers in multiquantum wells, the authors show that their results are fully consistent with previously reported data.
Investigation of carrier lifetime in 4H-SiC epilayers and lifetime control by electron irradiation
Authors: Danno Katsunori , Nakamura Daisuke , Kimoto Tsunenobu
Published: May 2007

Carrier lifetimes in 4H-SiC epilayers are investigated by differential microwave photoconductivity decay measurements. When the Z1∕2 concentration is higher than 1013cm−3, the Z1∕2 center works as a recombination center. In this case, carrier lifetimes show positive dependence on the injection level (number of irradiated photons). On the other hand, other recombination processes such as surface recombination limit the lifetime when the Z1∕2 concentration is lower than 1013cm−3. In this case, carrier lifetimes have decreased by increasing the injection level. By controlling the Z1∕2 concentration by low-energy electron irradiation, the lifetime control has been achieved.
Poly(ether sulfone) as a negative resist for electron beam lithography
Authors: Bryce R. M. , Freeman M. R. , Aktary M.
Published: May 2007

The sulfone containing polymer poly(butene sulfone) has long been used as positive electron beam resist due to the high scission rate of sulfone under electron irradiation. The authors demonstrate that poly(ether sulfone) acts as a high resolution negative electron beam resist which displays good chemical and dry-etch resistance. The electron beam exposure sensitivity at 10kV was found to be approximately 230μC∕cm2 for poly(ether sulfone), roughly 2.3 times that of poly(methyl methacrylate). As poly(ether sulfone) is a robust engineering polymer that can withstand etching this polymer is a suitable mask material and has properties of interest for direct incorporation in devices.
Lifetime improvement of green phosphorescent organic light-emitting diodes by charge confining device structure
Authors: Kim Sung Hyun , Jang Jyongsik , Lee Jun Yeob
Published: May 2007

Lifetime improvement of green phosphorescent organic light-emitting diodes by charge confinement inside an emitting layer was investigated. Excitons were confined within the emitting layer by using a charge confining structure with a high doping concentration at the center of the emitting layer. The lifetime of green devices could be improved by more than five times by confining the excitons at the center of the emitting layer.
High performance asymmetric graded index coupler with integrated lens for high index waveguides
Authors: Sun Rong , Nguyen Victor , Agarwal Anu , Hong Ching-yin , Yasaitis John , Kimerling Lionel , Michel Jurgen
Published: May 2007

The authors have demonstrated a planar, monolithically integrated lensed, asymmetric graded index fiber-to-waveguide coupler with 0.45dB coupling loss at 1550nm. The silicon-based coupler and the waveguides were fabricated entirely by complementary metal-oxide semiconductor compatible processes. They also observed an excellent broadband performance between 1520 and 1630nm. The average coupling loss was 0.4dB across the entire cathodoluminescence band (1530–1625nm).
Efficient multilayer white polymer light-emitting diodes with aluminum cathodes
Authors: Niu Xiaodi , Qin Chuanjiang , Zhang Baohua , Yang Junwei , Xie Zhiyuan , Cheng Yanxiang , Wang Lixiang
Published: May 2007

Efficient multilayer white polymer light-emitting diodes (WPLEDs) with aluminum cathodes are fabricated. The multilayer structure is composed of a water soluble hole-injection layer, a toluene-soluble emissive layer, and an alcohol-soluble emissive layer. The polarity difference of the solvents used for spin coating these polymers allows for realization of the multilayer polymer structure. The recombination zone confined at the interface of the two emissive polymers avoids exciton quenching by electrodes, and white emission is realized by harvesting photons emitted from the two emissive polymers. A maximum luminous efficiency of 16.9cd∕A and a power efficiency of 11.1lm∕W are achieved for this WPLED.
Optical amplification in Ho3+-doped transparent oxyfluoride glass ceramics at 750nm
Authors: Lahoz F. , Hernández S. E. , Capuj N. E. , Navarro-Urrios D.
Published: May 2007

Positive transient optical gain has been demonstrated in Ho3+-doped transparent oxyfluoride glass-ceramics. A pump and probe experiment has been designed to show this result. High power laser pulses at 532nm were used as the pump source to strongly populate the Ho3+S25:F45 level due to nonresonant ground state absorption. Low power cw laser radiation at 750nm was used as the probe beam. The signal beam stimulates the emission associated with the Ho3+S25:F45→I75 electronic transition at 750nm. In addition to this, the high power pump pulses provide population inversion between the S25:F45 and I75, initial and final states of the transition, respectively, giving rise to the optical amplification of the signal beam. A gain coefficient of 3.7cm−1 (∼16dB∕cm) was obtained for a pump energy density of about 135mJ∕cm2 and a signal beam power density of 6μW∕cm2.
The persistence niche: what makes it and what breaks it for two fire-prone plant species
Authors: Keith David A. , Tozer Mark G. , Regan Tracey J. , Regan Helen M.
Published: May 2007

Persistence niches are expected to favour qualitatively different plant life histories compared with regeneration niches. In fire-prone habitats, for example, resprouting plants may be expected to exploit persistence niches, whereas obligate-seeders by definition exploit regeneration niches. Resprouter life histories should be typified by high rates of survival, which may be offset by relatively low rates of growth and reproduction. This combination of characters is expected to result from trade-offs in resource allocation and because the longevity of individual plants should buffer their populations against the effects of recruitment failure. We asked whether two resprouting perennial shrubs, Epacris barbata Melville and Xanthorrhoea resinifera (Sol. Ex Kite) E.C.Nelson & D.J.Bedford, exhibited the life-history character combinations that are expected for species exploiting a persistence niche. We also investigated how a change in habitat suitability caused by the invasion of a root pathogen may limit the ability of these species to occupy persistence niches. Demographic censuses of several years’ duration in two populations of each species yielded estimates of vital rates that were consistent with the life-history profile expected for a persistence niche. Rates of background survival were high and rates of fire-related mortality were low in both species. As expected, these were associated with low rates of growth and seedling establishment, although rates of seed production and viability were relatively high in both species. The importance of survival was confirmed by stochastic population models, which showed that population viability was more sensitive to decreases in survival of mature plants and increases in fire mortality of established plants than to changes in other vital rates. Seedling growth rates were also relatively important in E. barbata. Populations of both species that had been infected by root rot disease, Phytophthora cinnamomi, had substantially reduced survival rates and, consequently, reduced population viability. These effects were more extreme in E. barbata than in X. resinifera. We conclude that processes that reduce survival, such as disease infection and habitat loss, rather than processes that impede seed production and recruitment mediate the persistence niche. However, we discuss the possibility that this dependency might be mitigated by high fecundity if infrequent conditions that permit large recruitment events have so far eluded detection.
Reintroduction of rare and endangered plants: common factors, questions and approaches
Authors: Guerrant Jr Edward O. , Kaye Thomas N.
Published: May 2007

The science of reintroduction for conservation purposes is young, and there is still much to learn about the practice. As a means to achieving biological goals of successfully establishing new populations to enhance a species survival prospects, and project goals, such as learning how to go about establishing new populations, reintroduction projects are best done as well designed scientific experiments that test explicit hypotheses. Focusing on a range of factors common to any reintroduction, we review several empirical reintroduction projects with respect to hypotheses tested, experimental materials and methods employed, and evaluate their success in both biological and project terms.
Seed quality for conservation is critically affected by pre-storage factors
Authors: Probert Robin , Adams John , Coneybeer Julia , Crawford Andrew , Hay Fiona
Published: May 2007

The quality of seed-conservation collections, and hence their value for species reintroduction or restoration, is critically dependent on factors operating in the period between the point of collection and arrival at environmentally controlled processing and storage facilities. The timing of the acquisition of desiccation tolerance and seed longevity in air-dry storage, in relation to mass maturity and the time of natural seed dispersal, varies across species. In some wild plant species, seed quality continues to improve up to, and possibly beyond, the point of dispersal. Holding immature berries of Solanum dulcamara L. and capsules of Digitalis purpurea L. under natural conditions enabled comparison of seed quality between seeds stored under natural conditions and those dried rapidly under seedbank dry-room conditions. While seeds from fully ripe (post-mature) capsules of D. purpurea were insensitive to different post-harvest drying treatments, seed quality declined when mature berries of S. dulcamara were held under natural conditions. These results emphasise that the selection of post-harvest treatment will not only depend on the maturity of collected seeds but also may vary across species depending on the fruit type. Except for subtropical and tropical coastal locations, ambient daytime conditions during the main seed-collecting season (November–February) across Australia can be expected to result in tolerable rates of seed deterioration for the duration of seed-collecting missions. However, because seed moisture levels can be considerably higher than when equilibrated with ambient relative humidity, post-harvest handling decisions should ideally be informed by measurements of seed moisture at the time of collection, and subsequently seed moisture should be monitored during transit.
The contribution of in vitro technology and cryogenic storage to conservation of indigenous plants
Authors: Bunn Eric , Turner Shane , Panaia Maggie , Dixon Kingsley W.
Published: May 2007

In vitro culture has enabled a variety of recalcitrant and threatened plant taxa to be micropropagated in the absence of viable conventional propagation methods. Cryogenic storage research has provided alternative protocols for efficient long-term germplasm storage for many plant species. Recent advances in tissue-culture methods such as somatic embryogenesis have enabled the production of >20 000 somatic embryos of a recalcitrant native Australian rush in a few months, far higher than other in vitro methods for these types of plants. Cryogenic protocols are reported for >30 species of Australian vascular plants, seed and numerous mycorrhizal fungi (mainly orchid spp.), greatly extending the range and type of material that can be stored through the application of cryogenic methods. The role of in vitro and cryogenic research initiatives in botanic gardens for plant biodiversity conservation and restoration is discussed, using examples of successful ex situ conservation through tissue-culture and cryogenic-storage research.
Rare plants in the Golden Gate Estuary (California): the relationship between scale and understanding
Authors: Fiedler Peggy L. , Keever Megan E. , Grewell Brenda J. , Partridge Douglas J.
Published: May 2007

We analysed 10 rare-plant projects conducted from 1982 to 2005 for trends in scientific findings, project costs, effort and efficacy. Our purpose was to determine whether generalisations about these factors can be found, and if so, whether they might be useful for designing and implementing successful future rare-plant endeavours. Analysis results revealed that rare plant species persist despite their restriction to a highly fragmented and degraded urbanised estuary of more than seven million people. Also important were the findings that with sufficient funding, successful rare-plant reintroduction is possible in the short-term at minimum. Habitat considerations, however, are paramount—i.e. habitat requirements of a rare species should be known before reintroduction for the restoration effort to be likely to be successful. Understanding ecosystem functions that support rare species, therefore, remains the highest priority for rare-plant restorationists. Project costs varied significantly, as expected, but a ‘middle ground’ provides necessary and sufficient funding to conduct most rare-plant work for one or a few species. Costs rise, but not linearly, when additional rare taxa are included. Given our experience is applicable elsewhere, taking an ecosystem approach to protection of rare flora is most successful and cost effective.
Phylogeography provides an evolutionary context for the conservation of a diverse and ancient flora
Authors: Byrne M.
Published: May 2007

Phylogeography can inform conservation strategies through assessment of genetic diversity that incorporates an evolutionary perspective, and allows evaluation within a geographical context, thus providing integration with other biogeographical information. Comparative phylogeography can identify significant historical processes that have had major influences on the biota and provides a historical context for understanding current species distributions. The phylogeographic patterns in the flora of south-western Australia are reviewed. Concordant patterns of lineage divergence in three unrelated taxa from separate families with widespread distributions indicate a common response to major historical processes involved in Pleistocene climatic fluctuations. Identification of highly divergent haplotypes in some species indicates areas that may represent refugia during times of climatic instability. Analysis of phylogeographic patterns in the flora of south-western Australia has revealed the influence of historical climate change in promoting high phylogenetic diversity within species that is comparable to the high species diversity that is well known in the Western Australian flora. Knowledge of historical influences and species responses provides an evolutionary context for conservation management strategies that facilitate the continued action of dynamic evolutionary processes.
Managing plant populations in fragmented landscapes: restoration or gardening?
Authors: Hobbs Richard J.
Published: May 2007

Ecosystem fragmentation results in major changes in several environmental and biotic parameters that affect the ability of plant populations to persist. All stages of the plant life cycle may be influenced in either negative or positive ways by the changed biophysical settings caused by fragmentation and associated changes in the surrounding landscape. This may result in plant populations being lost or significantly reduced from patches of native vegetation, leading to the need for active management intervention. This intervention may include management of threatening processes, reversal of ecosystem degradation, or the reintroduction of plants of species that have been lost from an area. These management actions range from preventative management through to active restoration. In the present paper I explore the question of whether there is a limit to the degree of intervention that is desirable in conservation terms, beyond which we are no longer conserving but rather cultivating and gardening, i.e. creating an artificial and potentially unsustainable system. I discuss this question in relation to management of remnant vegetation in urban and agricultural settings and suggest that a careful mix of species-based and process-based management is required for us to succeed in the goal of biodiversity conservation in fragmented landscapes.
Collateral benefit: unconscious conservation of threatened plant species
Authors: Kirkpatrick J. B.
Published: May 2007

In Europe, the conservation of rare or threatened plant species (ROTS) largely involves the manipulation of anthropogenic disturbance regimes rather than the mitigation of human-induced threatening processes, as has been the case in Australia. In Tasmania, there are many ROTS, especially those of the depleted and stock-grazed grasslands and grassy woodlands, which survive because, unconscious of the needs of ROTS, people have disturbed land in ways that suit their life-cycle requirements. Such species are found in quarries, in borrow pits, in scrapes, on roadsides, on track edges, on old roads, under introduced trees, in heavily grazed native pastures, in regenerating clearfell coupes and on mown ground. They are disturbance-dependent species, usually with poor competitive abilities. Many cannot survive stock-grazing. Unconscious conservation of these species needs to become conscious, in the European manner. Spatial heterogeneity in disturbance regimes is important for maintaining this set of species, whereas temporal heterogeneity is likely to lead to their doom.
Seed dormancy and germination stimulation syndromes for Australian temperate species
Authors: Merritt D. J. , Turner S. R. , Clarke S. , Dixon K. W.
Published: May 2007

Understanding seed germination biology and the dynamics of seed dormancy is essential to developing reliable germination techniques. This paper presents some new data and reviews recent findings from germination studies on Australian species, with respect to the role of temperature and moisture in the control of dormancy and germination. A seed-burial experiment was conducted over a 1-year period (January–December) with seeds of Acanthocarpus preissii Lehm., Astroloma xerophyllum (DC.) Sond., Gahnia grandis (Labill.) S.T.Blake, Goodenia scaevolina F.Muell. and Tersonia cyathiflora (Fenzl) J.W.Green to determine the fluctuations in temperature and moisture seeds naturally experience in the buried environment. All seeds became hydrated during autumn (March) while soil temperatures were >15°C, suggestive of a period of warm stratification before the onset of cooler winter temperatures appropriate for germination. Evidence of rapid wetting and drying of seeds in the soil environment was also present. Laboratory experiments testing stratification as a means for dormancy loss showed that several weeks of warm stratification at 26/13°C or 33/18°C promoted germination of Lomandra preissii (Endl.) Ewart, Marianthus bicolor (Putt.) F.Muell. and Xyris lanata R.Br. seeds. X. lanata seeds also responded to several weeks of cold stratification at 5°C. By integrating this new data with other published data on germination of Australian species, diagrammatic models of germination timing, dormancy syndromes and propagation strategies for temperate Australian species are presented as working hypotheses to help direct future research.
Seeing the wood and the trees—predicting the future for fragmented plant populations in Australian landscapes
Authors: Broadhurst Linda , Young Andrew
Published: May 2007

Australian landscapes face significant environmental challenges in the coming decade. The fragmentation of vegetation following broadscale land-clearing has rapidly altered critical genetic and demographic processes within and among the remnants that still reside in these landscapes. These perturbations threaten the long-term persistence of many species. Although considerable research has been directed towards the management of rare species, little is understood about how common and widespread species respond to these new challenges. In this paper we review the current state of knowledge regarding species biology for some key Australian taxonomic groups to develop broad predictions about the major threats to species persistence, particularly for some of the most common and widespread floral components of fragmented Australian landscapes. The main focus is on associations between reproductive strategy, vulnerability to demographic and genetic threats, and implications for fecundity.
Scientific approaches to Australian temperate terrestrial orchid conservation
Authors: Brundrett Mark C.
Published: May 2007

This review summarises scientific knowledge concerning the mycorrhizal associations, pollination, demographics, genetics and evolution of Australian terrestrial orchids relevant to conservation. The orchid family is highly diverse in Western Australia (WA), with over 400 recognised taxa of which 76 are Declared Rare or Priority Flora. Major threats to rare orchids in WA include habitat loss, salinity, feral animals and drought. These threats require science-based recovery actions resulting from collaborations between universities, government agencies and community groups.
Fungal identification by DNA-based methods in combination with compatibility testing by germination assays has revealed a complex picture of orchid–fungus diversity and specificity. The majority of rare and common WA orchids studied have highly specific mycorrhizal associations with fungi in the Rhizoctonia alliance, but some associate with a wider diversity of fungi. These fungi may be a key factor influencing the distribution of orchids and their presence can be tested by orchid seed bait bioassays. These bioassays show that mycorrhizal fungi are concentrated in coarse organic matter that may be depleted in some habitats (e.g. by frequent fire). Mycorrhizal fungi also allow efficient propagation of terrestrial orchids for reintroduction into natural habitats and for bioassays to test habitat quality.
Four categories of WA orchids are defined by the following pollination strategies: (i) nectar-producing flowers with diverse pollinators, (ii) non-rewarding flowers that mimic other plants, (iii) winter-flowering orchids that attract fungus-feeding insects and (iv) sexually deceptive orchids with relatively specific pollinators. An exceptionally high proportion of WA orchids have specific insect pollinators. Bioassays testing orchid-pollinator specificity can define habitats and separate closely related species. Other research has revealed the chemical basis for insect attraction to orchids and the ecological consequences of deceptive pollination. Genetic studies have revealed that the structure of orchid populations is influenced by pollination, seed dispersal, reproductive isolation and hybridisation. Long-term demographic studies determine the viability of orchid populations, estimate rates of transition between seedling, flowering, non-flowering and dormant states and reveal factors, such as grazing and competition, that result in declining populations.
It is difficult to define potential new habitats for rare orchids because of their specific relationships with fungi and insects. An understanding of all three dimensions of orchid habitat requirements can be provided by bioassays with seed baits for fungi, flowers for insects and transplanted seedlings for orchid demography. The majority of both rare and common WA orchids have highly specific associations with pollinating insects and mycorrhizal fungi, suggesting that evolution has favoured increasing specificity in these relationships in the ancient landscapes of WA.
Population-size effects on seeds and seedlings from fragmented eucalypt populations: implications for seed sourcing for ecological restoration
Authors: Krauss Siegfried L. , Hermanutz Luise , Hopper Stephen D. , Coates David J.
Published: May 2007

Ecological restoration of degraded habitats is a major conservation activity requiring the collection of large amounts of native seed. Seed production and the genetic quality of seed may be influenced by properties of the source population, such as population size and fragmentation, potentially having an impact on restoration goals. We assessed the population-size effects on seed production and seedling performance in two Western Australian wheatbelt eucalypts, Eucalyptus salmonophloia F.Muell. and E. salubris F.Muell. Both species were historically widespread and dominant, but, as a consequence of land-clearing for agriculture, now exist as small, highly fragmented populations throughout the western half of their range. Given their former importance in the landscape, these species will be critical in ecological restoration of the region. We assessed small (n = 6–12) and large (n > 200) remnant populations in a highly fragmented landscape and compared these to large unfragmented populations. Seed number per capsule was dependent on population size and fragmentation for E. salubris, but not for E. salmonophloia. Large, unfragmented populations of E. salubris produced more than twice the number of seeds per capsule (mean = 2.95) than small and/or fragmented populations. However, seed germination, seed weight, seedling survival and seedling vigour to 1 year were independent of population size or fragmentation in both species. Our results suggest that reduced population size and increased fragmentation can negatively affect pollen quantity and/or quality, thereby limiting seed production, although no fitness effects were observed post-seed maturation. We suggest that the relative absence of post-seed maturation fitness effects in these small fragmented populations are a consequence of (1) wide outcrossing resulting from long-distance dispersal of pollen by highly mobile birds among fragmented populations and/or (2) efficient pre- or post-zygotic selection against more homozygous zygotes within fruits so that only relatively outbred seeds mature. The consequences on seed collection for ecological restoration of reduced population size and increased fragmentation for these eucalypts may be fewer seeds for the same collecting effort, but no apparent fitness effects of mature seeds. However, caution should be exercised when harvesting seed from these smaller populations, as over-harvesting may have an impact on recruitment and hence long-term persistence.
Plant mating systems and assessing population persistence in fragmented landscapes
Authors: Coates David J. , Sampson Jane F. , Yates Colin J.
Published: May 2007

Population size and habitat disturbance are key factors likely to shape the mating system of populations in disturbed and fragmented landscapes. They would be expected to influence the availability and behaviour of the pollinator, the ability to find mates in self-incompatible species, inbreeding in self-compatible species and the size of the pollen pool. These in turn might be expected to influence key variables critical for population persistence such as seed production, seed germination and seedling fitness. Here we investigate mating-system variation in six rare species, i.e. Banksia cuneata, B. oligantha, Lambertia orbifolia (Proteaceae), Verticordia fimbrilepis subsp. fimbrilepis, Eucalyptus rameliana (Myrtaceae), Acacia sciophanes (Mimosaceae), and two common species, i.e. Calothamnus quadrifidus (Myrtaceae) and Acacia anfractuosa. All seven species are animal-pollinated relatively long-lived woody shrubs with mixed-mating systems. Population variation in mating-system parameters was investigated in relation to population size and habitat disturbance. We show that although the mating system will vary depending on pollination biology and life-history, as populations get smaller and habitat disturbance increases there is a trend towards increased inbreeding, smaller effective sizes of paternal pollen pools and greater variation in outcrossing among plants. From the species investigated in this study we have found that changes in the mating system can be useful indicators of population processes and can give valuable insight into the development of conservation strategies for the persistence of plant species following anthropogenic disturbance and landscape fragmentation.
The significance of ex situ seed conservation to reintroduction of threatened plants
Authors: Cochrane J. A. , Crawford A. D. , Monks L. T.
Published: May 2007

Ex situ seed conservation aims to support species survival in the wild. This can be achieved by contributing genetic material for reintroduction. The goals of reintroduction are to increase both plant and population numbers, create self-sustaining populations and ultimately remove a species from its threatened listing. Quality seed collections with a broad genetic base are required to achieve this goal. Storage conditions that minimise deterioration of seeds will maximise the quality of seeds available for future use. Additionally, ex situ seed conservation provides long-term insurance against species or genotype loss until actual or potential threats can be removed. As threats to biodiversity escalate the most judicious conservation strategies will be ones that combine available resources to provide the highest possible degree of protection. Banked seeds are available irrespective of season and periods of low fecundity. Forward planning of reintroduction projects can be achieved with knowledge of the quantity and quality of banked seed. This paper discusses the challenges facing ex situ seed conservation while highlighting the benefits of integrating ex situ seed storage and plant reintroduction to help provide for better conservation outcomes.
Characteristics and genesis of two strongly weathered soils in Samar, Philippines
Authors: Navarrete Ian A. , Asio Victor B. , Jahn Reinhold , Tsutsuki Kiyoshi
Published: May 2007

Very limited data have been published on the nature of strongly weathered soils in geologically young humid tropical islands. The study evaluated the characteristics and formation of 2 strongly weathered soils in the island of Samar, Philippines, one developed from slate (Bagacay soil) and the other from ultrabasic rock (Salcedo soil). Results revealed that the soils have generally similar morphological characteristics, particularly in terms of colour (2.5 YR-10 R), solum thickness (>5.0 m), and structure (granular to subangular blocky), although the Salcedo soil has much higher clay content than the Bagacay soil. Both soils have similar chemical properties (e.g. acidic, low exchangeable bases) except that the Salcedo soil has lower CEC values but higher exchangeable Na content, resulting in a higher base saturation. They also have high dithionite-extractable Fe contents and very low oxalate/dithionite ratios and are dominated by halloysite, kaolinite, gibbsite, goethite, hematite, and quartz in the clay fraction. Apparently as a result of its more weatherable ultrabasic parent rock and more stable geomorphic surface, the Salcedo soil shows more advanced weathering and soil development than the Bagacay soil. Salcedo soil is classified as Haplic Ferralsol (Dystric, Clayic, Rhodic) in the World Reference Base or very fine, sesquic, isohyperthermic, Rhodic Hapludox in the Soil Taxonomy. Bagacay soil is a Haplic Acrisol (Alumic, Hyperdystric, Clayic, Rhodic) or fine, kaolinitic, isohyperthermic, Typic Paleudult. The Salcedo soil has very high Ni and Cr contents inherited from its ultrabasic parent material. The study reveals that on the geologically young humid tropical island of Samar, the characteristics and genesis of strongly weathered soils are greatly affected by the geochemical characteristic of the parent rock material.
Long-term trends in fertility of soils under continuous cultivation and cereal cropping in southern Queensland. IX. Simulation of soil carbon and nitrogen pools using CENTURY model
Authors: Chilcott C. R. , Dalal R. C. , Parton W. J. , Carter J. O. , King A. J.
Published: May 2007

Cultivation and cropping of soils results in a decline in soil organic carbon and soil nitrogen, and can lead to reduced crop yields. The CENTURY model was used to simulate the effects of continuous cultivation and cereal cropping on total soil organic matter (C and N), carbon pools, nitrogen mineralisation, and crop yield from 6 locations in southern Queensland. The model was calibrated for each replicate from the original datasets, allowing comparisons for each replicate rather than site averages. The CENTURY model was able to satisfactorily predict the impact of long-term cultivation and cereal cropping on total organic carbon, but was less successful in simulating the different fractions and nitrogen mineralisation. The model firstly over-predicted the initial (pre-cropping) soil carbon and nitrogen concentration of the sites. To account for the unique shrinking and swelling characteristics of the Vertosol soils, the default annual decomposition rates of the slow and passive carbon pools were doubled, and then the model accurately predicted initial conditions. The ability of the model to predict carbon pool fractions varied, demonstrating the difficulty inherent in predicting the size of these conceptual pools. The strength of the model lies in the ability to closely predict the starting soil organic matter conditions, and the ability to predict the impact of clearing, cultivation, fertiliser application, and continuous cropping on total soil carbon and nitrogen.
Properties of regolith beneath lateritic bauxite in the Darling Range of south Western Australia
Authors: Kew G. A. , Gilkes R. J.
Published: May 2007

A morphological key has been developed for regolith that is exposed during mining of lateritic bauxite in the Darling Range of south Western Australia. The key distinguishes materials with different mineralogical and chemical properties. Iron oxide cemented (Zh) regolith has a gibbsitic matrix, quartz-rich (Zm) regolith has a gibbsite and kaolin matrix, and clay-rich (Zp) regolith has a kaolin matrix. An Si affinity element map (Si, Hf, Th) and a K affinity element group (K, Ba, Rb) are associated with granitic quartz-rich regolith and an Al/Fe element affinity group (Al, Fe, Ti, P, Ni, Co, Cu, Mn, Zn, Ga, Cr, V) is associated with clay and iron rich regolith. Doleritic regolith is generally associated with the Al/Fe affinity group. Although granite and granitic regolith exhibit similar element affinity groups, the abundance of elements within each is highly variable, which reflects the diversity in composition of granite within the region. The degree of euhedral character of clay-size platy crystals (kaolinite/gibbsite) does not differ for materials distinguished by the key, as both quartz-rich (Zm) and clay-rich (Zp) regolith and both granitic and doleritic saprolite contain subhedral kaolin crystals. The crystal size of platy kaolin (approximately 0.5 µm) is similar for different mine pits and for different regolith materials (Zm and Zp) within mine pits. There is a difference in halloysite tube length (0.52–1.18 µm) between mine pits, which may be related to the presence of weathered mica or to the alteration of halloysite in gibbsite-rich regolith. The internal and external diameters of halloysite tubes (about 0.11 and 0.24 µm) are similar for different mine pits and different regolith types within mine pits. The resin used during thin section preparation contains chlorine, so that determination of chlorine by EMPA provides a measure of the porosity of regolith material. A systematic negative relationship exists between chlorine concentration and total oxide weight % of porous regolith matrix determined by EMPA; both measurements provide an indication of the porosity of the clay matrix in regolith.