Academic literature on the topic 'Allocasuarina verticillata'

This work was carried out to determine the relative importance of the endomycorrhizal and (or) ectomycorrhizal association in species of Casuarina and Allocasuarina. Under axenic conditions, Pisolithus and Scleroderma isolates formed ectomycorrhizas with a mantle and a Hartig net on Allocasuarina verticillata but failed to form a Hartig net on Casuarina glauca. In a controlled soil system, C. glauca was inoculated with the endomycorrhizal fungus Glomus intraradices Schenck & Smith, and A. verticillata was inoculated with Pisolithus albus IR100 Bougher & Smith and (or) G. intraradices. Both symbionts significantly stimulated growth in both plant species. For A. verticillata, its growth response to ectomycorrhizal inoculation was higher than to endomycorrhizal inoculation. When both symbionts were inoculated, antagonism among the fungal isolates was observed with a higher ectomycorrhizal colonization. These results showed that A. verticillata was ectomycorrhizal dependent, whereas C. glauca was endomycorrhizal dependent. From a practical point of view, this study shows the importance of selecting compatible mycorrhizal fungi for developing successful inoculation programmes. In addition, it would help to further research and determine the effect of ecto- and endo-mycorrhizal symbiosis on the formation and function of N2-fixing actinorhizal nodules.Key words: Casuarinaceae, ectomycorrhizas, arbuscular mycorrhizas, plant growth.

Allocasuarina verticillata is an important species for biodiversity conservation on Kangaroo Island (South Australia) because it is the primary food source for the endangered glossy black-cockatoo, Calyptorhynchus lathami halmaturinus. Two potentially limiting factors, pollen and soil nutrients, were studied in the context of A. verticillata as foraging habitat for glossy black-cockatoos. Cone production was not limited by the amount of pollen available to female plants. The soils on which A. verticillata occurs on Kangaroo Island were low in nutrients. Available N, P and K were significantly increased via the application of slow-release fertiliser and the added nutrients resulted in a corresponding increase in the productivity of A. verticillata. The additional nutrients increased the number of cones produced on female branches, branch growth and potentially therefore, tree size. Since cone profitability appears to increase with tree size, the additional growth may also result in greater cone profitability in the long term. Adding slow-release fertiliser to small female A. verticillata trees and revegetation on sites with higher concentrations of soil nutrients would benefit the cockatoos. This is because other studies have shown that the cockatoos increase their foraging efficiency by cropping cones from large trees with greater cone profitability and branches with high densities of cones.

Leaf gigantism is an example of marked morphological variation associated with abrupt environmental gradients of increasing coastal exposure. This study characterises the morphology and anatomy of leaf gigantism in four species across two habitats on the coastal headlands of the Tasman Peninsula, Tasmania, Australia. In addition, the genetic basis and adaptive significance of leaf gigantism are examined. Leaf gigantism was characterised in Leptospermum scoparium, Acacia verticillata and Allocasuarina monilifera by greater thickness and succulence, and by greater thickness and increased support tissue in Allocasuarina crassa. Glasshouse-grown seedlings of each species derived from exposed and inland field sites showed that leaf gigantism has both genetic and environmental components. Leaf succulence and a slower growth rate were shown to be heritable in seedlings from the exposed site of L. scoparium and A. verticillata, indicating genetic differentiation. In the reciprocal translocation trial, the higher degree of stress tolerance (as measured by chlorophyll florescence) exhibited by seedlings of L. scoparium and A. verticillata from the exposed site demonstrated the adaptive significance of leaf gigantism in these species. The ecological and evolutionary implications of leaf gigantism on the Tasman Peninsula are discussed.

Aspects of the floral biology of Allocasuarina verticillata were recorded in a natural stand in Canberra, Australia. The trees are dioecious, and flowering took place during the autumn to spring months (May–October). The female inflorescence consists of over 100 individual flowers, which remained receptive for up to 12 weeks. The proportion of individual flowers pollinated increased gradually over this time. The advantage of a long female receptive phase is that each inflorescence can potentially receive pollen from a number of male sources. Duration from pollination to fertilisation was 53–83 days. Male inflorescences dehisced over a 3–9 week period depending upon air temperatures. Pollen germination was highest at 10˚C and 15˚C and poor at 5˚C, 20˚C and 25˚C. Pollen grains remained turgid at the lower temperatures for at least 3 days. Seed germinated well at temperatures between 10˚C and 25˚C but there was a marked decline at 30˚C. Stratification of seed is suggested as a standard practice in germination tests. Results are discussed in relation to developing tree improvement strategies for domestication of the family Casuarinaceae.

Allocasuarina verticillata (Lam.) L.A.S. Johnson is a widespread species in south-eastern Australia providing vegetation cover, protecting fragile soils and providing food for birds. Understanding the effects of gene flow on the recruitment patterns, genetic differentiation and structure of fragmented populations provides fundamental guidelines to underpin plant conservation strategies and activities. In this study, four spatially disjunct populations of A. verticillata were sampled to explore the effects of population size, reproductive patterns and pollen and seed dispersal on among-population genetic diversity, genetic differentiation and structure, using field survey and microsatellite marker techniques. It was found that stands of A. verticillata were predominantly sexually reproductive, but asexual reproduction through root suckering was an additional mode of reproduction. The reproductive success of A. verticillata is positively correlated with the effective population size rather than actual population size. The reduction in effective population size and increment of spatial isolation resulted in lower genetic diversity and higher inbreeding coefficient of progenies. Moderate pairwise genetic differentiation and weak genetic structure were identified. The results suggest that exogenous, wind-mediated pollen flow provides some maintenance of genetic diversity in the isolated stands. Seed dispersal appears mainly to be over short distances (i.e., within populations), but the infrequent transport of seeds between disjunct locations cannot be ruled out as another factor that may help maintain genetic diversity.

Woody thickening is a widespread phenomenon in the grassy woodlands of the world, often with deleterious effects on nature conservation values. We aimed to determine whether increasing the frequency of planned fire prevented woody thickening and improved conservation values in a Eucalyptus viminalis grassy woodland in the process of invasion by Allocasuarina verticillata (henceforth Allocasuarina) in Hobart, Tasmania, Australia. We used a before–after control intervention design. Ten plots from which detailed vegetation data were collected in 2018 (before the burns), 2019 (between burns), 2020 (between burns) and 2021 (after the burns) were randomly located in each of four blocks. Two of the blocks were burned in both 2018 and 2021. One block was burned only in 2021, and another was not burned at all. Mechanical thinning of Allocasuarina took place in 2021 in six plots in one unburned block and in three twice-burned plots. The fires were low intensity and patchy, reflecting the reality of planned burns in this environment. Thus, there were unburned plots mixed with burned plots in each of the three burned blocks. We compared changes in vegetation and cover attributes between a preburn survey in 2018 and a postburn survey in 2021, between five fire history/thinning classes (unburned, no thinning; unburned, thinning; twice burned; burned in 2018 only; burned in 2021 only). Fires in both 2018 and 2021 resulted in lower litter cover and higher exotic species richness than one fire in 2021. Exotic species richness increase between 2018 and 2021 was greater after fires in 2018 and 2021 than after a fire in 2021 alone. Exotic species richness was lowest six years after fire and highest one to three years after fire. The basal area of Allocasuarina was, counter-intuitively, less reduced by two fires in four years than by one. Mechanical thinning reduced shrub layer cover, which largely consisted of small trees, but did not affect basal area. Our data suggested that grass cover increased until five years after a fire, declining back to a low level by eight years. The implications of the results for conservation management are that the mechanical removal of young Allocasuarina may be successful in preventing its thickening and that burning at a five-year interval is likely to best maintain understorey conservation values. The counter-intuitive results related to Allocasuarina basal area emphasise the importance of understanding cumulative effects of fire regimes on fuel cycles and the consequent effects on tree mortality.

Two types of root nodule symbioses are known for higher plants, legume and actinorhizal symbioses. In legume symbioses, bacterial signal factors induce the expression of ENOD40 genes. We isolated an ENOD40 promoter from an actinorhizal plant, Casuarina glauca, and compared its expression pattern in a legume (Lotus japonicus) and an actinorhizal plant (Allocasuarina verticillata) with that of an ENOD40 promoter from the legume soybean (GmENOD402). In the actinorhizal Allocasuarina sp., CgENOD40-GUS and GmENOD40-2-GUS showed similar expression patterns in both vegetative and symbiotic development, and neither promoter was active during nodule induction. The nonsymbiotic expression pattern of CgENOD40-GUS in the legume genus Lotus resembled the nonsymbiotic expression patterns of legume ENOD40 genes however, in contrast to GmENOD40-2-GUS, CgENOD40-GUS was not active during nodule induction. The fact that only legume, not actinorhizal, ENOD40 genes are induced during legume nodule induction can be linked to the phloem unloading mechanisms established in the zones of nodule induction in the roots of both types of host plants.

On Kangaroo Island, the Glossy Black-Cockatoo Calyptorhynchus lathami halmaturinus relies on the kernels contained in the russet cones of the Drooping Sheoak Allocasuarina verticillata as its food source. Clearing of Drooping Sheoak woodland resulted in the decline of the Glossy Black-Cockatoo from the South Australian mainland by the late 1970s and the sub-species is now confined to Kangaroo Island. The purpose of this study was to identify the factors limiting cone production by the Drooping Sheoak and to determine if food was likely to be in shortage by studying the foraging behaviour of the cockatoos. The number of russet cones on Drooping Sheoak branches was significantly greater during the period from July 1995 to July 1996 than the period from December 1996 to July 1997. Rainfall was lowest during the latter period suggesting that rainfall may limit cone production. The mean number of pollen grains per male catkin was 334,280 in 1996 and 335,809 in 1997 and did not vary significantly between years. These observations show that rainfall probably did not affect pollen production. This may ensure that sufficient pollen is available to female inflorescences each year in a climate where rainfall varies between years. The period over which male trees dehisced pollen varied from 25 to 74 days each year from 1995 to 1997. Dehiscence accelerated after one to three days of high daily rainfall in 1995 and 1997, but it was protracted in 1996 when daily rainfall was low. Female trees, however, effectively flowered year-round because although the main flowering period was in July each year, inflorescences and cones were present throughout the year. Female Drooping Sheoaks may overcome the variation in the timing and duration of male pollen dehiscence by flowering for a longer period than males and by producing some inflorescences throughout the year. Catkin production varied significantly between regions on Kangaroo Island and pollen production per catkin also varied significantly between sites within Lathami Conservation Park. Although catkin and pollen production varied between regions and sites, pollen traps showed that female inflorescences would have received sufficient pollen to ensure pollination of all of their flowers during their receptive phase. The abundance of pollen on Kangaroo Island suggested that pollen availability would be unlikely to limit cone production. A hand pollination experiment showed that the amount of pollen available to female trees did not limit cone and seed production in the Drooping Sheoak. Of the 8,431 inflorescences marked in 1995, 1,638 or 19% set cones. Of the 3,444 inflorescences marked on the same trees in 1996, 609 or 18% set cones. The majority of inflorescences monitored took seven months to develop into mature russet cones in the first year and eight months in the second year. These patterns of cone development in the Drooping Sheoak suggested that cone production may be nutrient limited because low fruit set and slow fruit maturation typically result from soil nutrient limitation in other plants. The production of inflorescences and russet cones by Drooping Sheoaks was shown to be limited by soil nutrient levels because the application of combined slow-release fertiliser significantly increased female branch growth and inflorescence and russet cone production. Applying slow-release fertiliser to female Drooping Sheoaks could potentially increase the foraging efficiency of Glossy Black-Cockatoos and their food intake rates. This is because fertilising female Drooping Sheoaks significantly increased the number of russet cones per branch and Glossy Black-Cockatoos preferentially foraged on branches with high numbers of russet cones present. Over a period of 22 months, Glossy Black-Cockatoos returned to forage on individual trees at a greater rate than would be expected by chance, demonstrating that they favoured certain individual Drooping Sheoaks for foraging. A cone removal experiment was conducted to test the hypothesis that harvesting of cones by the cockatoos may allow the sheoaks to direct additional resources into cone and seed production the following year. However, removal of cones from female Drooping Sheoaks did not affect cone, seed or kernel production over the two years of observation. This suggests that the resources allocated to cone retention by Drooping Sheoaks are small in comparison with the resources allocated to flowering and cone maturation. Glossy Black-Cockatoos favoured large female Drooping Sheoaks for foraging and apparently avoided small trees because foraged trees had significantly larger stem girth and canopy radius than non-foraged trees. The female Drooping Sheoaks adjacent to foraged trees were comparable in height, cone abundance and cone profitability. Although the size of the cone crop increases linearly with stem girth in Drooping Sheoaks, habitat and tree use by the cockatoos was not related to cone abundance on Kangaroo Island. Large trees must, therefore, be favoured for reasons other than access to more cones or more profitable cones. The Glossy Black-Cockatoos on Kangaroo Island spent no more than four minutes per day flying, foraged in a mean of five trees per day and harvested cones from no more than five positions (bouts) per tree. Comparison of branches used and not used for foraging by the cockatoos showed that they harvested cones from branches with significantly more russet cones present. The number of russet cones per branch and girth were negatively correlated suggesting that the cockatoos did not forage in large trees because they carry more cones on their branches than small trees. This also suggests that the cockatoos located branches from which to crop cones once inside the canopy. By foraging in large trees and cropping cones from branches with high densities of russet cones, the cockatoos only had to make a small number of movements between Drooping Sheoaks and within the canopies of the sheoaks when foraging. Consequently, the energetic costs of foraging for Glossy Black-Cockatoos on Kangaroo Island were low compared with other Black-Cockatoo species. When breeding, the cockatoos spent significantly more time per day foraging. They also cropped cones in significantly more bouts per tree and this resulted in the harvesting of significantly more cones per tree than non-breeding birds. This shows that when breeding, the cockatoos increased their energy intake without increasing movement between trees, simply by cropping more cones per tree than non-breeding birds. Two possible explanations may account for why Glossy Black-Cockatoos spent very little time and energy moving between Drooping Sheoaks and within the canopies of the trees. First, trees and cones may be abundant in the habitats used for feeding so that the cockatoos do not have to make a large number of movements to harvest their food requirements. Non-breeding birds spent only 26% of their time foraging and breeding birds spent only 36% of their time foraging. The cockatoos had cropped cones from only 20% of the trees and 13% of the branches surveyed. The small proportion of time spent foraging by Glossy Black-Cockatoos on Kangaroo Island, combined with the small proportion of trees and branches used for foraging indicates that the amount of habitat and available exceeded that required for foraging by the cockatoo population in the habitats used for foraging. Second, the number of movements made by Glossy Black-Cockatoos between Drooping Sheoaks when foraging may be related to the risk of predation. That is, the cockatoos may reduce the risk of predation by limiting the number of movements they make when foraging. Females appeared to be more wary of predators than males during time-budget observations because they foraged further inside the canopy (where cones are significantly larger) and frequently paused to monitor the movement of avian predators when foraging. Both of these behaviours would have contributed to the significantly longer cone processing times recorded for females than males. Glossy Black-Cockatoos may not breed in regions of Kangaroo Island where the amount of Drooping Sheoak habitat (i.e. the number of large trees) is limited near nest sites. One reason for this may be because the additional investment of time and energy in movement prohibits the cockatoos from collecting sufficient energy to raise young. Another reason may be that the risk of predation may be too great in regions where the cockatoos have to make a large number of movements between feeding trees per day to collect food. This may account for why few birds raise young on the eastern end of the Island where the area of feeding habitat near the nest sites is relatively small. This study has shown that revegetation with Drooping Sheoak close to nest hollows is likely to increase the number of breeding attempts and nesting success on Kangaroo Island.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2005