School of Ecosystem and Forest Sciences - Research Publications
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ItemNo Preview AvailableSeed supply for broadscale restoration: maximizing evolutionary potential(WILEY, 2008-11-01)Restoring degraded land to combat environmental degradation requires the collection of vast quantities of germplasm (seed). Sourcing this material raises questions related to provenance selection, seed quality and harvest sustainability. Restoration guidelines strongly recommend using local sources to maximize local adaptation and prevent outbreeding depression, but in highly modified landscapes this restricts collection to small remnants where limited, poor quality seed is available, and where harvesting impacts may be high. We review three principles guiding the sourcing of restoration germplasm: (i) the appropriateness of using 'local' seed, (ii) sample sizes and population characteristics required to capture sufficient genetic diversity to establish self-sustaining populations and (iii) the impact of over-harvesting source populations. We review these topics by examining current collection guidelines and the evidence supporting these, then we consider if the guidelines can be improved and the consequences of not doing so. We find that the emphasis on local seed sourcing will, in many cases, lead to poor restoration outcomes, particularly at broad geographic scales. We suggest that seed sourcing should concentrate less on local collection and more on capturing high quality and genetically diverse seed to maximize the adaptive potential of restoration efforts to current and future environmental change.
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ItemWood density and its radial variation in six canopy tree species differing in shade-tolerance in western Thailand(OXFORD UNIV PRESS, 2009-08-01)BACKGROUND AND AIMS: Wood density is a key variable for understanding life history strategies in tropical trees. Differences in wood density and its radial variation were related to the shade-tolerance of six canopy tree species in seasonally dry tropical forest in Thailand. In addition, using tree ring measurements, the influence of tree size, age and annual increment on radial density gradients was analysed. METHODS: Wood density was determined from tree cores using X-ray densitometry. X-ray films were digitized and images were measured, resulting in a continuous density profile for each sample. Mixed models were then developed to analyse differences in average wood density and in radial gradients in density among the six tree species, as well as the effects of tree age, size and annual increment on radial increases in Melia azedarach. KEY RESULTS: Average wood density generally reflected differences in shade-tolerance, varying by nearly a factor of two. Radial gradients occurred in all species, ranging from an increase of (approx. 70%) in the shade-intolerant Melia azedarach to a decrease of approx. 13% in the shade-tolerant Neolitsea obtusifolia, but the slopes of radial gradients were generally unrelated to shade-tolerance. For Melia azedarach, radial increases were most-parsimoniously explained by log-transformed tree age and annual increment rather than by tree size. CONCLUSIONS: The results indicate that average wood density generally reflects differences in shade-tolerance in seasonally dry tropical forests; however, inferences based on wood density alone are potentially misleading for species with complex life histories. In addition, the findings suggest that a 'whole-tree' view of life history and biomechanics is important for understanding patterns of radial variation in wood density. Finally, accounting for wood density gradients is likely to improve the accuracy of estimates of stem biomass and carbon in tropical trees.
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ItemInteractive effects of high irradiance and moderate heat on photosynthesis, pigments, and tocopherol in the tree-fern Dicksonia antarctica(CSIRO PUBLISHING, 2009-01-01)Effects of high irradiance and moderate heat on photosynthesis of the tree-fern Dicksonia antarctica (Labill., Dicksoniaceae) were examined in a climate chamber under two contrasting irradiance regimes (900 and 170 µmol photons m-2 s-1) and three sequential temperature treatments (15°C; 35°C; back to 15°C). High irradiance led to decline in predawn quantum yield of photochemistry, Fv/Fm (0.73), maximal Rubisco activity (Vcmax; from 37 to 29 µmol m-2s-1), and electron transport capacity (Jmax; from 115 to 67 µmol m-2 s-1). Temperature increase to 35°C resulted in further decreases in Fv/Fm (0.45) and in chlorophyll bleaching of high irradiance plants, while Vcmax and Jmax were not affected. Critical temperature for thylakoid stability (Tc) of D. antarctica was comparable with other higher plants (c. 47°C), and increases of Tc with air temperature were greater in high irradiance plants. Increased Tc was not associated with accumulation of osmotica or zeaxanthin formation. High irradiance increased the xanthophyll cycle pigment pool (V+A+Z, 91 v. 48 mmol mol-1 chlorophyll-1), de-epoxidation state (56% v. 4%), and α-tocopherol. Temperature increase to 35°C had no effect on V+A+Z and de-epoxidation state in both light regimes, while lutein, β-carotene and α-tocopherols increased, potentially contributing to increased membrane stability under high irradiance.
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ItemEffects of sudden exposure to high light levels on two tree fern species Dicksonia antarctica (Dicksoniaceae) and Cyathea australis (Cyatheaceae) acclimated to different light intensities(CSIRO PUBLISHING, 2009-01-01)We examined the responses of two tree fern species (Dicksonia antarctica and Cyathea australis) growing under shade or variable light (intermittent shade) to sudden exposure to high light levels. Steady-state gas exchange as well as dynamic responses of plants to artificial sunflecks indicated that difference in growth light environment had very little effect on the tree ferns' capacities to utilise and acclimate to prevailing light conditions. Two weeks of exposure to high light levels (short-term acclimation) led to decreases in all photosynthetic parameters and more negative predawn frond water potentials, mostly irrespective of previous growth light environments. After 3months in high light levels (long-term acclimation), D. antarctica fully recovered, while C. australis previously grown under variable light, recovered only partially, suggesting high light level stress effects under the variable light environments for this species.
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ItemThe development of descending projections from the brainstem to the spinal cord in the fetal sheep(BMC, 2007-06-18)BACKGROUND: Although the fetal sheep is a favoured model for studying the ontogeny of physiological control systems, there are no descriptions of the timing of arrival of the projections of supraspinal origin that regulate somatic and visceral function. In the early development of birds and mammals, spontaneous motor activity is generated within spinal circuits, but as development proceeds, a distinct change occurs in spontaneous motor patterns that is dependent on the presence of intact, descending inputs to the spinal cord. In the fetal sheep, this change occurs at approximately 65 days gestation (G65), so we therefore hypothesised that spinally-projecting axons from the neurons responsible for transforming fetal behaviour must arrive at the spinal cord level shortly before G65. Accordingly we aimed to identify the brainstem neurons that send projections to the spinal cord in the mature sheep fetus at G140 (term = G147) with retrograde tracing, and thus to establish whether any projections from the brainstem were absent from the spinal cord at G55, an age prior to the marked change in fetal motor activity has occurred. RESULTS: At G140, CTB labelled cells were found within and around nuclei in the reticular formation of the medulla and pons, within the vestibular nucleus, raphe complex, red nucleus, and the nucleus of the solitary tract. This pattern of labelling is similar to that previously reported in other species. The distribution of CTB labelled neurons in the G55 fetus was similar to that of the G140 fetus. CONCLUSION: The brainstem nuclei that contain neurons which project axons to the spinal cord in the fetal sheep are the same as in other mammalian species. All projections present in the mature fetus at G140 have already arrived at the spinal cord by approximately one third of the way through gestation. The demonstration that the neurons responsible for transforming fetal behaviour in early ontogeny have already reached the spinal cord by G55, an age well before the change in motor behaviour occurs, suggests that the projections do not become fully functional until well after their arrival at the spinal cord.
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ItemProapoptotic BH3-only proteins trigger membrane integration of prosurvival Bcl-w and neutralize its activity(ROCKEFELLER UNIV PRESS, 2003-09-01)Prosurvival Bcl-2-like proteins, like Bcl-w, are thought to function on organelles such as the mitochondrion and to be targeted to them by their hydrophobic COOH-terminal domain. We unexpectedly found, however, that the membrane association of Bcl-w was enhanced during apoptosis. In healthy cells, Bcl-w was loosely attached to the mitochondrial membrane, but it was converted into an integral membrane protein by cytotoxic signals that induce binding of BH3-only proteins, such as Bim, or by the addition of BH3 peptides to lysates. As the structure of Bcl-w has revealed that its COOH-terminal domain occupies the hydrophobic groove where BH3 ligands bind, displacement of that domain by a BH3 ligand would displace the hydrophobic COOH-terminal residues, allowing their insertion into the membrane. To determine whether BH3 ligation is sufficient to induce the enhanced membrane affinity, or to render Bcl-w proapoptotic, we mimicked their complex by tethering the Bim BH3 domain to the NH2 terminus of Bcl-w. The chimera indeed bound avidly to membranes, in a fashion requiring the COOH-terminal domain, but neither promoted nor inhibited apoptosis. These results suggest that ligation of a proapoptotic BH3-only protein alters the conformation of Bcl-w, enhances membrane association, and neutralizes its survival function.
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ItemReduced cortical inhibition in a mouse model of familial childhood absence epilepsy(National Acad Sciences, 2007)Mutations in the GABA(A) receptor gamma2 subunit are associated with childhood absence epilepsy and febrile seizures. To understand better the molecular basis of absence epilepsy in man, we developed a mouse model harboring a gamma2 subunit point mutation (R43Q) found in a large Australian family. Mice heterozygous for the mutation demonstrated behavioral arrest associated with 6-to 7-Hz spike-and-wave discharges, which are blocked by ethosuximide, a first-line treatment for absence epilepsy in man. Seizures in the mouse showed an abrupt onset at around age 20 days corresponding to the childhood nature of this disease. Reduced cell surface expression of gamma2(R43Q) was seen in heterozygous mice in the absence of any change in alpha1 subunit surface expression, ruling out a dominant-negative effect. GABA(A)-mediated synaptic currents recorded from cortical pyramidal neurons revealed a small but significant reduction that was not seen in the reticular or ventrobasal thalamic nuclei. We hypothesize that a subtle reduction in cortical inhibition underlies childhood absence epilepsy seen in humans harboring the R43Q mutation.
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ItemNo Preview AvailableSoil-atmosphere greenhouse gas exchange in a cool, temperate Eucalyptus delegatensis forest in south-eastern Australia(ELSEVIER, 2009-03-11)Forests are the largest C sink (vegetation and soil) in the terrestrial biosphere and may additionally provide an important soil methane (CH₄) sink, whilst producing little nitrous oxide (N₂O) when nutrients are tightly cycled. In this study, we determine the magnitude and spatial variation of soil-atmosphere N₂O, CH₄ and CO₂ exchange in a Eucalyptus delegatensis forest in New South Wales, Australia, and investigate how the magnitude of the fluxes depends on the presence of N₂-fixing tree species (Acacia dealbata), the proximity of creeks, and changing environmental conditions. Soil trace gas exchange was measured along replicated transects and in forest plots with and without presence of A. dealbata using static manual chambers and an automated trace gas measurement system for 2 weeks next to an eddy covariance tower measuring net ecosystem CO₂ exchange. CH₄ was taken up by the forest soil (-51.8μg CH₄-Cm⁻² h⁻¹) and was significantly correlated with relative saturation (S r) of the soil. The soil within creek lines was a net CH₄ source (up to 33.5μg CH₄-Cm⁻² h⁻¹), whereas the wider forest soil was a CH₄ sink regardless of distance from the creek line. Soil N₂O emissions were small (<3.3μg N₂O-Nm⁻² h⁻¹) throughout the 2-week period, despite major rain and snowfall. Soil N₂O emissions only correlated with soil and air temperature. The presence of A. dealbata in the understorey had no influence on the magnitude of CH₄ uptake, N₂O emission or soil N parameters. N₂O production increased with increasing soil moisture (up to 50% S r) in laboratory incubations and gross nitrification was negative or negligible as measured through ¹⁵N isotope pool dilution. The small N₂O emissions are probably due to the limited capacity for nitrification in this late successional forest soil with C:N ratios >20. Soil-atmosphere exchange of CO₂ was several orders of magnitude greater (88.8mg CO₂-Cm⁻² h⁻¹) than CH₄ and N₂O, and represented 43% of total ecosystem respiration. The forest was a net greenhouse gas sink (126.22kg CO₂-equivalents ha⁻¹ d⁻¹) during the 2-week measurement period, of which soil CH₄ uptake contributed only 0.3% and N₂O emissions offset only 0.3%.
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ItemInteractions between timber harvesting and swamp wallabies (Wallabia bicolor): Space use, density and browsing impact(ELSEVIER SCIENCE BV, 2007-12-15)
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ItemStormwater harvesting: Assessing operational system performance(Informa UK Limited, 2008-01-01)