Showing papers in "Australian Journal of Botany in 2010"

Savanna woody plant dynamics: the role of fire and herbivory, separately and synergistically

Abstract: Althoughthedemographyofwoodyplantsinsavannashaslongbeenshowntobeduetomanyfactors,therestill is no consensus as to the relative importance of the top-down processes of fire and herbivory, nor on how fire and herbivory affect plant demography. We review the recent literature and suggest that further progress depends on the following: (i) a demographic framework with clear terminology and which focuses on recruitment, transitions and mortality, (ii) an understandingofmechanismsofhow fireactuallydamagesplantsandhowplantssurviveandout-growthisdamage,mainly throughheight,barkthicknessordiametergrowth,(iii)anunderstandingofhowlossesinbiomassduetoherbivorymayaffect plant demography and, (iv) a consideration of interactions between fire and herbivory. Our synthesis suggests (i) strong recruitment limitation as well as some evidence of transition limitation by both fire and herbivory, (ii) that in some cases herbivory alone, notably by elephants and impala, can be more significant than fire alone, on woody plant population size, (iii) that fire and herbivory together are a lethal combination for woody plants and, (iv) that differences in strategies and responses of savanna plants to fire and herbivory are poorly explored.

Ageing mallee eucalypt vegetation after fire: insights for successional trajectories in semi-arid mallee ecosystems

Abstract: A critical requirement in the ecological management of fire is knowledge of the age-class distribution of the vegetation. Such knowledge is important because it underpins the distribution of ecological features important to plants and animals including retreat sites, food sources and foraging microhabitats. However, in many regions, knowledge of the age-class distribution of vegetation is severely constrained by the limited data available on fire history. Much fire-history mapping is restricted to post-1972 fires, following satellite imagery becoming widely available. To investigate fire history in the semi-arid Murray Mallee region in southern Australia, we developed regression models for six species of mallee eucalypt (Eucalyptus oleosa F.Muell. ex. Miq. subsp. oleosa, E. leptophylla F.Muell. ex. Miq., E. dumosa J. Oxley, E. costata subsp. murrayana L. A. S. Johnson & K. D. Hill, E. gracilis F.Muell. and E. socialis F.Muell. ex. Miq.) to quantify the relationship between mean stem diameter and stem age (indicated by fire-year) at sites of known time since fire. We then used these models to predict mean stem age, and thus infer fire-year, for sites where the time since fire was not known. Validation of the models with independent data revealed a highly significant correlation between the actual and predicted time since fire (r = 0.71, P 35 years since fire). Nevertheless, this approach enables examination of post-fire chronosequences in semi-arid mallee ecosystems to be extended from 35 years post-fire to over 100 years. The predicted ages identified for mallee stands imply a need for redefining what is meant by ‘old-growth’ mallee, and challenges current perceptions of an over-abundance of ‘long-unburnt’ mallee vegetation. Given the strong influence of fire on semi-arid mallee vegetation, this approach offers the potential for a better understanding of long-term successional dynamics and the status of biota in an ecosystem that encompasses more than 250 000 km2 of southern Australia.

Effects of soil temperature regimes after fire on seed dormancy and germination in six Australian Fabaceae species

Abstract: In addition to direct fire cues such as heat, smoke and charred wood, the passage of fire leads indirectly to changes in environmental conditions which may be able to break physical dormancy in hard-coated seeds. After a fire, the open canopy and the burnt material lying on the surface alter the thermal properties of the soil, resulting in elevated soil temperatures for long periods of time. We simulated daily temperature regimes experienced at different depths of soil profile after a summer fire. Our aim was to determine whether these temperature regimes and the duration of exposure (5, 15 and 30 days) play an important role breaking physical seed dormancy in six legumes from south-eastern Australia. Our results showed that simulated temperature regimes break seed dormancy. This effect is specially pronounced at temperatures that are expected to occur near the soil surface (0–2 cm depth). The duration of exposure interacts with temperature to break dormancy, with the highest germination rates reached after the longest duration and highest temperatures. However, the germination response varied among species. Therefore, this indirect post-fire cue could play a role in the regeneration of plant communities, and could stimulate seedling emergence independent of direct fire cues as well as in interaction with direct cues.

A wide diversity of epicormic structures is present in Myrtaceae species in the northern Australian savanna biome – implications for adaptation to fire

Abstract: Recent research has shown that the eucalypts of southern Australia have an unusual and apparently fire-adapted epicormic structure By studying a range of myrtaceous species from northern Australia we hoped to determine if this structure was also present in northern eucalypts We anatomically examined the epicormic structures from 21 myrtaceous species in 11 genera from the north of the Northern Territory, Australia An extremely wide diversity of epicormic structures was found, ranging from buds absent, buds at or near the bark surface, to bud-forming meristems in the innermost bark These Myrtaceae species displayed a far greater variation in epicormic structure than recorded in any other family This is possibly a reflection of the importance of the resprouter strategy, a long fire history in Australia and the ecological diversification of the Myrtaceae Nonetheless, all the investigated eucalypts (northern and southern) possessed the same specialised, apparently fire-adapted, epicormic structure This is remarkably consistent given the taxonomic, geographical and morphological diversity of the eucalypts

Differential responses to allelopathic compounds released by the invasive Acacia dealbata Link (Mimosaceae) indicate stimulation of its own seed

Abstract: Invasion by exotic species constitutes a major threat to natural ecosystems. One of the most invasive species of current concern in Europe is Acacia dealbata Link (Mimosaceae), the expansion of which is reducing populations of native species, and hence biodiversity. To investigate the potential involvement of allelopathic mechanisms in this process, we evaluated the germination and seedling growth performance of Lactuca sativa L. (Compositae), Zea mays L. (Gramineae), Dactylis glomerata L. (Gramineae), Arabidopsis thaliana (L.) Heynh. (Cruciferae) and A. dealbata, in the presence of mixtures of throughfall and litter leachate and of aqueous soil extracts collected under A. dealbata at different times of the year. Each test species responded differently to the solutions being assayed suggesting that A. dealbata allelochemicals may affect a variety of physiological growth parameters. In most cases the observed effects were stimulatory rather than inhibitory, which may have long-term deleterious effects on native plant populations since premature growth during periods of poor resources can be detrimental. Interestingly, increased radical growth of A. dealbata was detected with either extract suggesting a positive autoalleloapthy effect.

Resprouting and mortality of juvenile eucalypts in an Australian savanna: impacts of fire season and annual sorghum

Abstract: In northern Australian savannas, canopy tree species often have juvenile tree banks that are composed mainly of small individuals of indeterminate age that have resprouted repeatedly after fire. Little is known about their demography. We report the initial responses (mortality, topkill and resprouting type) of 3133 marked juvenile eucalypts to set fires of different seasons (early dry season, late dry season, wet season, unburnt) in a 32 400 m2 field experiment. Fire treatments were repeated in plots dominated by a native annual grass (sorghum) that becomes senescent before the early dry season and provides the main fuel of savanna fires, and in others with little or no sorghum, but instead other native grasses and forbs that remain green well into the dry season. Most juvenile eucalypts 22% in the low-intensity early dry season fire in plots with little or no annual sorghum, compared with <2% in all other fire/understorey combinations. We suggest results are related to fire behaviour, seasonal carbohydrate storage dynamics and competition with ground-layer plants.

Delayed emergence and post-fire recruitment success: effects of seasonal germination, fire season and dormancy type

Abstract: Delayed seedling emergence can negatively affect plant recruitment. Recent work has shown that some species with innate seasonal requirements for germination can have seedling emergence delayed, depending on the season of fire. The impact of this delay, which is in relation to both resprouters and seedlings of species that emerge independent of season, remains unknown. I assessed delayed emergence and subsequent impacts on post-fire recruitment success of three Leucopogon species, which all display a seasonal emergence pattern related to their physiological dormancy. Intra-population comparisons showed that both small (1–6 months) and much larger (12–15 months) delays of emergence reduced seedling survival and growth, and increased the time taken for plants to reach maturity. Fire season induced delays produced very similar results, with higher mortality and slower growth after winter fires compared with post-summer fire cohorts. Seasonal emergence patterns, associated with seed dormancy and germination cues, may therefore provide a mechanism that determines the variation of recruitment success after fires in different seasons. A better understanding of the relationship between fire season and timing of emergence of physiologically dormant species would be timely considering the forecast widening of the fire season due to climate change.

Environmental influence on the physico-chemical and physiological properties of Jatropha curcas seeds

Abstract: The present study investigated the influence of two Brazilian environments on the physico-chemical and physiological properties of Jatropha curcas L. (physic nut) – an oilseed plant of great potential in biodiesel production. Fruits and seeds of plants grown in the Brazilian Atlantic rainforest (AF) and in the semiarid climate of Caatinga (SA) were compared. Fruits from the SA were longer, wider and heavier than those from the AF. In contrast, the AF seeds were larger and heavier than the SA seeds. Soluble sugars, protein, relative water content and electrical conductivity of the SA seeds significantly exceeded that of the AF seeds by 28%, 23%, 32% and 94%, respectively. Seeds of the AF had a significantly greater percentage germination (17.5%) and needed less time to germinate (10%) than did the SA seeds. Shoot dry biomass of seedlings grown from the AF seeds significantly exceeded that of the SA by 18.5%. Results suggest this pattern may be due to the higher carbon storage (i.e. sugars, proteins and oil) in the AF than SA seeds. Further studies are warranted to verify whether the differences observed between the seed sources investigated in the present study could be due to varietal or biotype factors.

Origin and evolution of the South American endemic Artemisia species (Asteraceae): evidence from molecular phylogeny, ribosomal DNA and genome size data

Abstract: Genus Artemisia is thought to have reached the Americas across the Bering Strait from Asia during the late Tertiary, but the systematic position of the South American endemic species and the migration routes towards the south have not yet been studied. We used nuclear DNA sequences to unravel the interspecific relationships among the South American Artemisia and their connections with the remaining species of the genus, as well as using fluorescent in situ hybridisation and genome size assessments to characterise this polyploid complex. Most of the species are clustered in a monophyletic clade, nested within the American endemic clade, with the exception of A. magellanica Sch. Bip., which appears segregated from the other American species and constitutes a clade together with A. biennis Willd. Fluorescent in situ hybridisation and genome size data revealed that monoploid genome size remains quite constant across ploidy levels and a proportional increase of ribosomal loci was detected, a dynamic not usually found in this genus. The results are discussed in the light of evolutionary processes which occur in plants, and plausible origins for the South American endemic species are hypothesised.

Mycosporine-like amino acids profile and their activity under PAR and UVR in a hot-spring cyanobacterium Scytonema sp. HKAR-3

Abstract: The cyanobacterium Scytonema sp. HKAR-3 isolated from a hot spring in India was investigated for the presence of mycosporine-like amino acids (MAAs) and their induction under PAR and PAR+UVR. High-performance liquid-chromatograph (HPLC) analysis revealed the presence of two MAAs, mycosporine–glycine (λmax = 310 nm) and an unknown MAA-334 (λmax = 334 nm), with retention times of 4.1 and 8.7 min, respectively. This is the first report for the presence of two MAAs and, in particular, the synthesis of mycosporine–glycine in any strain of Scytonema. There was no effect of radiation type (PAR or PAR+UVR) on the synthesis of mycosporine–glycine; however, the synthesis of MAA-334 was found to be higher in samples receiving PAR+UVR than in those receiving PAR only. There was a circadian induction in the synthesis of MAAs under alternate 12-h light (PAR or PAR+UVR) and dark periods. MAAs were found to be induced mostly during the light period and their production dropped again during the dark period. This suggests that the synthesis of MAAs is an energy-dependent process and depends on solar energy for its maintenance in natural habitats.

Leaf anatomy and histochemistry of Lippia citriodora (Verbenaceae)

Abstract: Lippia citriodora H.B.K. is an aromatic plant indigenous to South America. It is cultivated and commercialised as an ornamental for its lemon-like scent emitted from its leaves and flowers. The present morphoanatomical and histochemical study revealed that leaves of L. citriodora possess one type of setae (non-glandular) and at least five types of glandular trichomes, with the latter differing anatomically and in the composition of their secondary metabolites. Scanning electron microscopy revealed that the same types of trichomes exist also on the calyces. Histochemical tests indicate that the glandular trichomes contain a combination of terpenoids, flavonoids, carbohydrates, phenolics and alkaloids. However, within the vacuoles of the mesophyll cells, terpenoids, phenolics, flavonoids and tannins are stored. The presence of lamellar cytoplasmic inclusions in the mesophyll cells, possibly precursors of tannins stored in the vacuoles, is reported for the first time.

Fire intensity, serotiny and seed release in 19 woody species: evidence for risk spreading among wind-dispersed and resprouting syndromes

Abstract: Seed storage in woody fruits on plants has been much studied, whereas trait variation in seed release has been given scant attention. In non-Mediterranean climates, some species release seeds immediately after fire, whereas others retain seeds in open fruits/cones for longer. We expected that species with wind-dispersed seeds and those killed by fire would spread their recruitment risks by having stronger cues for fruit opening and slower seed release once fruits were open. We therefore tested whether fire intensity (heat) affected fruit opening and seed release in 19 species. We then contrasted fruit opening and seed release among (1) serotiny levels (weak, moderate, strong), (2) dispersal (wind v. unassisted) and (3) resprouting ability (killed v. resprout) traits. Only three species required heat for fruit opening. Most species, however, retained varying proportions of seeds in open fruits. Strongly and moderately serotinous species retained seeds in open fruits longer than did weakly serotinous species. Both species with wind-dispersed seeds and fire-killed species required stronger heat effects for fruits to open but retained seeds in open fruits longer than did species with alternative traits. By delaying seed release after fruits have opened, species with wind-dispersed seeds, and those that are killed by fire, maximise the ability of seeds to arrive at safe sites after fire.

Nutrient responses differ between node and organogenic cultures of Corymbia torelliana × C. citriodora (Myrtaceae)

Abstract: Hybrids between Corymbia torelliana (F.Muell.) K.D.Hill & L.A.S.Johnson and C. citriodora subsp. variegata (F.Muell.) A.R.Bean & M.W.McDonald are used extensively for plantation forestry in subtropical eastern Australia; however, plantation establishment has been hampered by inadequate seed supply and variable amenability to propagation as rooted cuttings. The present study investigated node-culture and organogenic-culture methods for in vitro propagation of two families of juvenile Corymbia hybrids. The effects of nutrient and auxin concentrations on root formation, shoot elongation and shoot proliferation, and subsequent conversion to plantlets in an in vitro soil-less system, were assessed. The response to the nutrient concentration differed between organogenic and node cultures. Half-strength, compared with full-strength, medium with auxin increased shoot proliferation by 58% for one family in the node culture, in which many shoots form roots and elongate rapidly in the absence of cytokinin. However, full-strength medium increased shoot proliferation by 213% over that in the half-strength medium for the other family in the organogenic culture, in which shoots do not form roots in the presence of cytokinin, and nutrient uptake occurs via callus and stem tissue rather than roots. The auxin, naphthalene acetic acid, sometimes stimulated root formation and shoot elongation in the node culture, although it had no effect on the final number of shoots. Most shoots (57–100%) subsequently formed roots in the in vitro soil-less medium. The high rates of proliferation and plantlet conversion in the present study provide the means, not only for simultaneous laboratory storage and field-testing of Corymbia clones before selection of desired genotypes, but also for en masse plantlet production of selected clones or families for plantation establishment.

Restoration treatments improve seedling establishment in a degraded Mediterranean-type Eucalyptus ecosystem

Abstract: Restoration of degraded Mediterranean-type ecosystems (MTEs) with long, hot and dry summers is challenging. To develop management guidelines, we evaluated techniques that could improve seedling establishment in two degraded Eucalyptus gomphocephala DC (tuart) woodlands, given weed and herbivore control. These techniques aimed to mimic favourable conditions for species that primarily recruit following disturbance events (e.g. fire). Trial 1 investigated the response of 5-month-old seedlings and broadcast seed in plots that contained a created ashbed, were ripped, or were ripped and contained an ashbed. Trial 2 examined the response of 5-month-old seedlings to treatments providing a nutrient or moisture source (slow-release fertiliser tablet, chelating agent, slow-release fertiliser tablet plus chelating agent, zeolite, hydrated hydrophilic co-polymers and dry hydrophilic co-polymers). Results indicated that created ashbeds enhance establishment for a range of species and reduce weed cover, with or without ripping. Broadcast seeding was not successful in returning species to site. Higher growth rates were recorded in seedlings treated with a nutrient source. The present study has shown that it is possible to re-establish local plant species in degraded woodlands through several techniques that mimic disturbance (e.g. fire). Strong early growth may be the vital start seedlings need in MTEs in the face of reinvading weed species, herbivory and a drying climate.

Decades-scale vegetation change in burned and unburned alpine coniferous heath

Abstract: Fire appears to be a rare event in alpine vegetation, suggesting that its effects might be more persistent than in most lowland vegetation types. However, it has been suggested that the Australian alpine biota is resilient to infrequent large fires. This paper describes decades-scale vegetation and soil change after fire in paired plots overfire boundaries in Tasmanian alpine coniferous heath. The effect of fire on soils persisted for decades. Recovery of vegetation was extremely slow by global standards, with delayed reinvasion of previously dominant species. There was low cover of the most fire-sensitive species 43–69 years after fire and much bare ground still evident, with the rate of revegetation declining through time. Gymnosperm shrubs increased at the expense of angiosperms in the unburned plots in the same period and cryptogams declined in both burned and unburned plots. These results suggest that the Tasmanian alpine flora cannot be characterised as resilient to infrequent large fire, although most species survive its incidence. The many centuries that it appears are necessary for coniferous heath to recover to its pre-burn state suggest that fires caused by increased ignitions from lightning and arsonists are the major issue for conservation of the vegetation type.

Fire regimes and interval-sensitive vegetation in semiarid Gregory National Park, northern Australia

Abstract: Few data are available concerning contemporary fire regimes and the responses of fire interval-sensitive vegetation types in semiarid woodland savanna landscapes of northern Australia. For a 10 300 km2 semiarid portion of Gregory National Park, in the present paper we describe (1) components of the contemporary fire regime for 1998–2008, on the basis of assessments derived from Landsat and MODIS imagery, (2) for the same period, the population dynamics, and characteristic fine-fuel loads associated with Acacia shirleyi Maiden (lancewood), an obligate seeder tree species occurring in dense monodominant stands, and (3) the fire responses of woody species, and fine-fuel dynamics, sampled in 41 plots comprising shrubby open-woodland over spinifex hummock grassland. While rain-year (July–June) rainfall was consistently reliable over the study period, annual fire extent fluctuated markedly, with an average of 29% being fire affected, mostly in the latter part of the year under relatively harsh fire-climate conditions. Collectively, such conditions facilitated short fire-return intervals, with 30% of the study area experiencing a repeat fire within 1 year, and 80% experiencing a repeat fire within 3 years. Fine fuels associated with the interior of lancewood thickets were characteristically small ( 10 years. Of 133 woody species sampled, all trees (n = 26), with the exception of A. shirleyi, were resprouters, and 58% of all shrub species (n = 105) were obligate seeders, with observed primary juvenile periods <5 years. Assembled data generally supported observations made from other northern Australian studies concerning the responses of fire-sensitive woody taxa in rugged, sandstone-derived landscapes, and illustrated the enormous challenges facing ecologically sustainable fire management in such settings. Contemporary fire regimes of Gregory National Park are not ecologically sustainable.

In situ seed development and in vitro regeneration of three difficult-to-propagate Lepidosperma species (Cyperaceae)

Abstract: Field studies of fruit production from Lepidosperma concavum R.Br., L. laterale R.Br. and L. longitudinale Labill.showedthatlargeproportions(21-77%)offruitswereunfilledandthat filledandunfilledfruitslookedalike.Bagging ofinflorescencesdemonstratedthat filledfruitstendedtobeshed,whileemptyfruitsremainedwithintheinflorescence.Time of collection was critical for obtaining viable seeds, with successful harvesting limited to a short period (weeks) after maturation.Thetimingof floweringandfruitmaturationwerefairlyconsistentbetweenspecies,populationsandyearsinour studyarea.InL.concavumfruitproductionwasincreasedincultivationcomparedwithwildpopulations.Inallthreespecies, verylittleornogerminationoffruitsoccurredundernurseryconditions.Invitrocultureinitiationwasattemptedusingintact fruits, nicked fruits and seeds on 1/2MS (Murashige and Skoog) medium with 1 mM zeatin and 0.5 mM gibberellic acid in darkness.Cultureofintactfruitresultedinnogermination,whilenickedfruitshowedsomegerminationresponse.Bestresults were achieved from seeds with germination occurring as early as 7 to 18 days depending on the species. Germination of L.concavum,L.lateraleandL.longitudinalewas86%,64%and83%respectivelywithin5weeks.Germinationresponsewas strongly influenced by seed maturity. Mature seeds germinated significantly faster than immature seeds. On a small proportion of cultured seeds, calli formed and differentiated into numerous plantlets on growth regulator-free medium. Given the promising results observed in this study, in vitro culture appears to be a practical means of mass propagating Lepidosperma species.

Ontogenetic, anatomical and histochemical study of the extrafloral nectaries of Sapium biglandulosum (Euphorbiaceae)

Abstract: The present paper aims to confirm the nature of secretory structures found on the petiole and leaf margins of Sapium biglandulosum Muell. Arg. The anatomy, ontogenesis and histochemistry were studied by light microscopy, whereas mono- and disaccharides in the exudates were detected by high performance liquid chromatography. The exudate from the petiole had a total sugar concentration of 32.5% (w/v), of which 38.1% was fructose, 43.7% glucose and 18.2% sucrose. The petiolar gland started its development from a group of meristematic cells that underwent asynchronous divisions. At the end of the ontogenesis, a well structured vascularised gland made up of a palisade secretory epidermis, secretory parenchyma and a secretory pore was observed. Leaf-margin glands showed a similar anatomy. Histochemical tests revealed the presence of proteins, pectins, carbohydrates, tannins and anthocyanins. On the basis of our results, there is compelling evidence that the studied glands are in fact extrafloral nectaries.

Biological indicators of climate change: evidence from long-term flowering records of plants along the Victorian coast, Australia

Abstract: We investigate the utility of using historical data sources to track changes in flowering time of coastal species in south-eastern Australia in response to recent climate warming. Studies of this nature in the southern hemisphere are rare, mainly because of a paucity of long-term data sources. Despite this, we found there is considerable potential to utilise existing data sourced from herbaria collections and field naturalists’ notes and diaries to identify native plant species suitable as biological indicators of climate change. Of 101 candidate species investigated in the present study, eight were identified as showing a general trend towards earlier flowering over time, indicating a correlation with increasing temperatures. There was some evidence to suggest that species which flower in spring and summer may be more sensitive to changes in temperature. There was a high level of uncertainty regarding the detection of trends, which was a function of the accessibility, abundance and accuracy of the various data sources. However, this uncertainty could be resolved in future studies by combining the datasets from the present study with field monitoring of phenological cycles in climatically different locations. Data held by community groups could be made more accessible if there was a concerted effort to fund collation and digitisation of these records. This might best be achieved by working with community groups, and facilitated through the recent establishment of a community phenological observation database in Australia.

Aboveground biomass of functional groups in the ground layer of savannas under different fire frequencies

Abstract: Savannas with different fire histories should have differences in aboveground biomass due to varying responses of functional groups. We investigated the effects of different fire frequencies on total aboveground biomass and also the biomass of functional groups (the tussock grass Tristachya leiostachya Nees, other grasses, small woody individuals) and dry biomass in savannas subjected to annual fires, biennial fires, and protected from fire for 12 years. Total biomass in the protected area was more than twice that of the annually burned area. T. leiostachya aboveground biomass was higher in the protected area than in annually and biennially burned areas, which were not different. Biomass of other grasses was lower in the protected area, whereas woody biomass values did not differ among areas. In the biennially burned and protected areas, we found a positive relationship between T. leiostachya and dry biomass. In the annually burned area, T. leiostachya biomass was negatively correlated with the biomass of other grasses and woody individuals. This negative correlation supports the idea that frequent fires favour the former, and may indicate an outcompeting effect. Knowledge not only about biomass but especially about its functional components is necessary to understand the processes and management consequences of different burning strategies.

Histology of organogenesis and somatic embryogenesis in excised root cultures of an endangered species Tylophora indica (Asclepiadaceae)

Abstract: This paper reports an efficient regeneration protocol through parallel organogenic and embryogenic pathways from green root segments (GRSs) of Tylophora indica (Burm.f) Merrill. GRSs explants from one year old in vitro cultures were cultured on Murashige and Skoog (MS) medium containing various cytokinins. Five µmol/L of 6-benzyladenine (BA) was most responsive for organogenesis in 1.5 cm long GRSs. Repeated subculture on medium containing both BA (5 µmol/L) and 1-naphthleneacetic acid (NAA) (0.1 µmol/L) promoted multiplication and proliferation of direct shoot buds (46.80 ± 0.96) and callus mediated somatic embryogenesis (18.07 ± 0.33). Germinated embryos isolated from callus were transferred onto maturation medium consisting of half-strength MS medium either devoid of plant growth regulators (PGRs) or with various concentrations of gibberellic acid (GA). Microshoots were excised during subculture and transferred onto root induction medium, thus ensuring a continuous supply of germplasm. Morphogenic variations were noticed in types of roots induced on various auxins. Regenerated plantlets and emblings hardened best on vermiculite with a survival rate of 90% and 70% respectively. However, the emblings were healthier in comparison to the regenerated plants. Histological analysis showed the origin and development of organogenesis.

Mycorrhizal specificity of Diuris fragrantissima (Orchidaceae) and persistence in a reintroduced population

Abstract: This study investigated the diversity and specificity of mycorrhizal fungi associated with five Diuris (Orchidaceae) taxa in south-eastern Australia, as part of a reintroduction program for the endangered species Diuris fragrantissima. We compared fungi isolated from D. fragrantissima occurring naturally in the only remaining population with those from artificially cultivated plants and reintroduced plants 18 months after planting in a new field site west of Melbourne. Genetic similarity of nuclear internal transcribed spacer and nuclear large subunit DNA sequences showed that Diuris taxa associate with a narrow taxonomic range of fungi within the cosmopolitan family Tulasnellaceae in the Rhizoctonia alliance. All fungal isolates induced host seed germination and hence were considered mycorrhizal. Fungal isolates from naturally occurring D. fragrantissima plants showed a higher level of genetic similarity than fungi isolated from cultivated plants. This observation suggests that, historically, the species may have associated with a more genetically variable range of Tulasnella fungi. Artificially cultivated D. fragrantissima were propagated aseptically from seed and spontaneously formed mycorrhizal associations within 6 months of transfer to potting media. Wild collected D. fragrantissima plants maintained in cultivation for over 30 years were found to contain mycorrhizal fungi similar to those isolated from naturally occurring plants in 2004–2006. Mycorrhizal associations in artificially cultivated D. fragrantissima were present in 18 randomly sampled plants 18 months after reintroduction. Further, associations formed between several reintroduced plants and a fungus concurrently inoculated into site soil. We propose that future orchid reintroductions may benefit from the concurrent addition of suitable mycorrhizal fungi to site soil. Maintenance of orchid mycorrhizal relationships after reintroduction is essential to improve long-term viability of reintroduced populations.

Soil seedbank composition and dynamics across alpine summits in south-eastern Australia.

Abstract: Alpine soil seedbanks are generally regarded as small and unimportant to regeneration. Here, we investigate for the first time the composition of the readily germinable soil seedbank across alpine summits in south-eastern Australia. We aimed to compare the species in the seedbank with the standing vegetation, show seasonal variations in seedbank composition and identify regeneration strategies of alpine seedbank species. By using standard glasshouse and cold-stratification germination techniques, the germinable soil seedbank across the study region was found to comprise 39 species from 25 families, with species from the Asteraceae the most common. Persistent seedbanks were found across all eight alpine summits (1668–1970 m), comparable in seed density (150 ± 27 to 1330 ± 294 per m2) with those of other alpine areas in the northern and southern hemispheres. The density of germinable seeds varied widely among sites and between collection times (autumn, spring) and there were no trends in seed density with altitude. The qualitative and quantitative similarity between the seedbank species and the standing vegetation was low. Correlations between the proportions of species in regeneration categories (from obligate seeders, through to vegetative regenerators) in the standing vegetation and the seedbank were also poor. Our results indicate a divergence between the species in the current standing vegetation and those present in the readily germinable soil seed bank. The current patterns and predominance of seed-regenerating species in the seedbank indicate that these species may have an important role to play in regulating and contributing to future changes in the vegetation assemblage.

High genetic diversity in a clonal relict Alexgeorgea nitens (Restionaceae): implications for ecological restoration

Abstract: The importance of genetic issues associated with the sourcing of propagules is increasingly recognised for successful ecological restoration. A consideration of life history traits has contributed to ‘best-guess’ scenarios on the appropriate location and desirable properties of local provenance source populations, but these can lack precision. For clonal species, population genetic structure and variation will depend on the balance between the extent and growth rate of asexual clones, sexual reproduction, pollen dispersal, and subsequent seed dispersal and recruitment. We assessed patterns of population genetic structure and variation for Alexgeorgea nitens (Nees) L. Johnston & B. Briggs (Restionaceae), a dioecious, clonal, perennial species, with novel life history traits. Our results show high levels of genetic diversity within populations, and surprisingly low levels of population differentiation (ΦST = 0.17). We suggest that the high genetic diversity observed within these populations reflects extensive pollen dispersal and successful seeding (sexual reproduction) and recruitment events, even though direct observations of seedling recruitment are rare. In this case, a ‘best-guess’ propagule-sourcing scenario based on life-history traits that appear to limit dispersal capability does not predict the extent of high local genetic diversity and weak population genetic structure in A. nitens.

Do generalisations of global trade-offs in plant design apply to an Australian sclerophyllous flora?

Abstract: Functional-trait analysis at a global scale has found evidence for evolutionary specialisation of species into those designed to acquire resources rapidly and those designed to conserve resources. The present study aimed to determine whether such a trade-off exists in sclerophyllous vegetation in Australia. We measured 10 traits for 167 plant species. The first axis of a principal components analysis represented a trade-off between resource acquisition and resource conservation, consistent with global trends. Common traits shared by resource-conservative species included low specific leaf area (SLA), resprouting, ant-dispersal, and ericoid mycorrhizal and ectomycorrhizal associations. These attributes were typical of 3 of 13 functional groups produced by cluster analysis (eucalypts, ant-dispersed shrubs, ericoid heaths) that had the lowest SLA, and were almost exclusively native shrubs and trees. Resource-acquisitive species had high SLA, a small stature, annual life cycle, arbuscular mycorrhizal or non-mycorrhizal associations, and small, wind-dispersed seeds. These attributes are similar to those identified for species with a ruderal strategy and were typical of the functional groups representing wind-dispersed composites, AM annuals and non-mycorrhizal annuals that had the highest SLA and were dominated by introduced species. Comparable trait associations have been found in other studies, suggesting that similar processes drive plant design at a global scale. However, there were some patterns specific to the flora studied that were attributable to adaptations to suit the nutrient-poor soils and arid conditions typical of the Australian environment.

Seed ecology of the invasive woody plant African Olive (Olea europaea subsp. cuspidata): Implications for management and restoration

Abstract: Knowledege of the seed ecology of invasive exotic species, including soil seedbank dynamics, is essential to understanding key factors in successful invasion and in identifying management opportunities. African Olive, Olea europaea L. subsp. cuspidata, is an exotic invasive woody plant in Hawaii, Norfolk Island and eastern Australia, and is now well established in the Cumberland Plain region of western Sydney, Australia. In the present study, the key aspects of the seed ecology of African Olive were determined for populations in western Sydney. Extracted seed germinated at a wide range of temperatures, consistent with tolerance of a wide range of climatic conditions. A seed-burial experiment indicated a slow decrease in viability down to 70.3% during the first year, followed by a rapid decline down to 14.7% in the second year. Probit analysis indicated that under field conditions, seed persistence in the soil was ~29 months (2.4 years). In situ germination was low (3.3%) and did not occur until the mechanical constriction of the endocarp was released through decomposition. The woody seed endocarp was found to be permeable to water, indicating that physical dormancy was not imposed by providing a barrier to water uptake. Within its invasive range, African Olive produces abundant seed. However, the rapid loss of viability of soil-stored seed results in a narrow window of opportunity for germination. The short persistence of seed in the soil may provide an opportunity for managers to achieve control of African Olive once mature plants are removed.

Microsporogenesis and microgametogenesis of Cardiospermum grandiflorum and Urvillea chacoensis (Sapindaceae, Paullinieae)

Abstract: Microsporogenesis and microgametogenesis of two species, Cardiospermum grandiflorum Sw. and Urvillea chacoensis Hunz. (Sapindaceae, Paullinieae), were studied using light and transmission electron microscopy. Both species are monoecious, with staminate and hermaphrodite, although functionally pistillate, flowers. A comparative pollen-development study of these two floral morphs is reported. For the present study, five stages of pollen ontogeny were identified. The development of the anther wall is of basic type. Its wall consists of epidermis, endothecium, two middle layers and a uninucleate secretory tapetum. The microspore tetrads are tetrahedral. The mature anther in staminate flowers presents the endothecium with well developed fibrillar thickenings, remains of tapetal cells, a single locule formed in the theca by dissolution of the septum before anther dehiscence and two-celled pollen grains when shed. In functionally pistillate flowers, the mature anthers present remnants of the middle layers, tapetal cells without signs of degradation, the theca with two locules and pollen grains uni- or bicellular, some of them with the cytoplasm collapsed. These anthers are not dehiscent. It can be concluded that male sterility is characterised by failure to produce functional pollen grains, an event that would be associated with the persistence of tapetal cells. Ultrastructural analysis clearly shows the difference in tapetal cells between the two flower morphs.

Pollination ecology of the rare desert species Eremosparton songoricum (Fabaceae)

Abstract: The pollination ecology of Eremosparton songoricum (Litv.) Vass., a rare desert species endemic to central Asia, was examined by a series of observational studies and manipulative experiments in two natural populations during 2007–2008. Results showed that the duration of flowering lasted 21 and 23 days, respectively, in Populations A and B from late May to late June in 2008. Anthesis of a single flower often lasted for 3 days. However, if pollinators were excluded, both the anthesis and stigma receptivity lasted 2 days longer. Mating-system experiment showed that E. songoricum was self-compatible and pollination success relied on pollinators. Fruit set after bagging without emasculation was 0.02 ± 0.01%. This suggested that spontaneous autogamy rarely happened. E. songoricum primarily relies on a combination of large floral display, secretion of nectar and a yellow ‘nectar guide’ on the standard to further attract pollinators, which may be the result of adaptation to a habitat with unreliable access to pollinators. A single flower produced ~0.18 μL and 0.50 μL of nectar during 2 days in Populations A and B, respectively. The peak secretion occurred at 1300–1500 hours, which overlapped with the climax of visitation of the effective pollinators at 1300–1400 hours. There were four effective pollinators in both populations, namely Colletes popovi Nosk., Megachile terminate Morawitz, Coelioxys sp. and Bembix planifrons F.Mor. The most frequent one, Colletes popovi Nosk., was observed pollinating many flowers of the same individual plant (65.8 ± 1.1%) in Population A, suggesting that geitonogamous self-pollination is unavoidable. Inbreeding depression played a role during the period from fertilisation to fruit maturation.

Evidence of pseudomonad pollen formation in Hypolytrum (Mapanioideae, Cyperaceae)

Abstract: Cyperaceae are characterised by typical simultaneous microsporogenesis that results in the formation of pseudomonad pollen. Morphological studies indicate the occurrence of a distinct pollen type in Mapanioideae, the spherical and monoporate Mapania-type pollen, found in representatives of Hypolytreae. This study investigates anther and pollen development in species of Hypolytrum for a better understanding of the mapanioid pollen type. Stages in microsporogenesis and microgametogenesis were analysed in both Hypolytrum (Mapanioideae, Hypolytreae; five species sampled) and Rhynchospora (Cyperoideae; two species studied). The latter was used as a comparator, known for the occurrence of pseudomonads. The results presented here confirm those already reported for the family, regardless of genus. The most important differences are morphological, not developmental. All species sampled of both genera had Cyperaceae-type simultaneous microsporogenesis resulting in pseudomonad pollen. Predictions that Mapania-type pollen in Hypolytrum would be monad are refuted. Anthers examined of Rhynchospora showed phenolic idioblasts, while those of species of Hypolytrum did not. There is need for ontogenetic studies on the other genera of Hypolytreae, such as Mapania and Scirpodendron, to extend and test the generality of our observations across the Hypolytreae.

Effect of storage temperature on spore viability and early gametophyte development of three vulnerable species of Alsophila (Cyatheaceae)

Abstract: To effectively preserve the vulnerable species of Alsophila, we studied the effects of varying the temperature and duration of storage on spore viability, early gametophyte development and the microstructure of brown spores of three Alsophila species. Spores of A. spinulosa (Wall. ex Hook.) Tryon and A. gigantea Wall. ex Hook. lost viability quickly when stored at room temperature and suffered from great loss when stored at –18°C from 6 to 12 months. Within 1 month, spore viability of A. spinulosa and A. gigantea stored at 4°C was higher than that of those stored in liquid nitrogen. In contrast, long-term storage in liquid nitrogen resulted in a comparatively small loss of viability for these two species. The spores of A. podophylla Hook. died within 3 months after storage at room temperature, 4°C and –18°C, and they died within 12 months when stored in liquid nitrogen. The spores of A. spinulosa and A. gigantea stored at room temperature, 4°C and –18°C, were prone to develop into abnormal gametophytes. These results suggest that storage of A. spinulosa and A. gigantea spores in liquid nitrogen is an effective method of preserving these vulnerable species. The reasons for the failure to preserve ephemeral A. podophylla spores by storage in liquid nitrogen are discussed.