I am a plant ecologist with a particular interest in arid environments, primarily in Australia but also other parts of the world, such as Kazakhstan and southern USA. Prior to coming to UTS in 2007, my research was focused on leaf structure-function relationships. This research included leaf hydraulics with Prof NM Holbrook (Harvard University) and leaf shape and temperature with Dr Adrienne Nicotra (The Australian National University) for my doctoral studies.
My current emphasis is on leaf function and survival at extreme high temperatures. I am fascinated with plants living in the apparently harsh conditions of arid regions, namely extreme high temperatures coupled with low irregular rainfall. High temperature extremes are predicted to increase in both intensity and frequency in the future. I am interested in learning how and which plants will survive these increased extremes.
I have been chairing a Leaf Temperature Working Group funded by the ARC-NZ Network for Vegetation Function that is modeling the effect of small-scale microclimatic changes on leaf thermal dynamics. To validate theory, I am a strong believer in field research, where I use a range of physiological and microclimatic methodologies to measure plant responses to high temperature extremes.
Audio links describing my research:
Can supervise: YES
I am interested in understanding how leaves avoid critical damage and death in extreme high temperature conditions. A particular focus is the influence of leaf morphology on leaf temperature regulation, especially under hot, dry conditions when cooling via transpiration is limited. Insight from this work will ultimately provide predictive power to vegetation models mapping species distribution in Australia under future climate scenarios.
Research areas include:
- Leaf-level responses to high temperature extremes due to microclimatic wind speed variability under desert field conditions.
- Leaf spectral properties and their association with other leaf traits, both within species and at cross-species scales.
- Plant responses to human- and animal-induced landscape modifications such as grazing and regulation of inland water systems.
I coordinate and teach:
Biocomplexity 91123 (1st year core): the diversity of life on earth - evolution, structure and function.
Alpine and Lowland Ecology 91163 (3rd year block elective): field-based learning along an altitudinal gradient from sea level to Australia’s highest point, Mt Kosciuszko.
Forest and Mountain Ecology 91371 (3rd year block elective): field-based learning along a north-south gradient up the Great Dividing Range through forests from Barrington Tops to the Border Ranges.
Semi-arid Ecology 91370 (3rd year block elective): field-based learning in arid and semi-arid western NSW.
I also teach:
Undergraduate Research Internship 60701 (3rd year elective): individual research project on arid plant ecology, aimed to develop research inquiry, procedure and enthusiasm (also a nice preparation for Honours or Masters).
Drake, J.E., Tjoelker, M.G., Vårhammar, A., Medlyn, B.E., Reich, P.B., Leigh, A., Pfautsch, S., Blackman, C.J., López, R., Aspinwall, M.J., Crous, K.Y., Duursma, R.A., Kumarathunge, D., De Kauwe, M.G., Jiang, M., Nicotra, A.B., Tissue, D.T., Choat, B., Atkin, O.K. & Barton, C.V.M. 2018, 'Trees tolerate an extreme heatwave via sustained transpirational cooling and increased leaf thermal tolerance.', Global change biology, vol. 24, no. 6, pp. 2390-2402.View/Download from: UTS OPUS or Publisher's site
Heatwaves are likely to increase in frequency and intensity with climate change, which may impair tree function and forest C uptake. However, we have little information regarding the impact of extreme heatwaves on the physiological performance of large trees in the field. Here, we grew Eucalyptus parramattensis trees for 1 year with experimental warming (+3°C) in a field setting, until they were greater than 6 m tall. We withheld irrigation for 1 month to dry the surface soils and then implemented an extreme heatwave treatment of 4 consecutive days with air temperatures exceeding 43°C, while monitoring whole-canopy exchange of CO2 and H2 O, leaf temperatures, leaf thermal tolerance, and leaf and branch hydraulic status. The heatwave reduced midday canopy photosynthesis to near zero but transpiration persisted, maintaining canopy cooling. A standard photosynthetic model was unable to capture the observed decoupling between photosynthesis and transpiration at high temperatures, suggesting that climate models may underestimate a moderating feedback of vegetation on heatwave intensity. The heatwave also triggered a rapid increase in leaf thermal tolerance, such that leaf temperatures observed during the heatwave were maintained within the thermal limits of leaf function. All responses were equivalent for trees with a prior history of ambient and warmed (+3°C) temperatures, indicating that climate warming conferred no added tolerance of heatwaves expected in the future. This coordinated physiological response utilizing latent cooling and adjustment of thermal thresholds has implications for tree tolerance of future climate extremes as well as model predictions of future heatwave intensity at landscape and global scales.
Leigh, A., Sevanto, S., Close, J.D. & Nicotra, A.B. 2017, 'The influence of leaf size and shape on leaf thermal dynamics: does theory hold up under natural conditions?', Plant, Cell and Environment, vol. 40, no. 2, pp. 237-248.View/Download from: UTS OPUS or Publisher's site
Laboratory studies on artificial leaves suggest that leaf thermal dynamics are strongly influenced by the two-dimensional size and shape of leaves and associated boundary layer thickness. Hot environments are therefore said to favour selection for small, narrow or dissected leaves. Empirical evidence from real leaves under field conditions is scant and traditionally based on point measurements that do not capture spatial variation in heat load. We used thermal imagery under field conditions to measure the leaf thermal time constant () in summer and the leaf-to-air temperature difference (T) and temperature range across laminae (Trange ) during winter, autumn and summer for 68 Proteaceae species. We investigated the influence of leaf area and margin complexity relative to effective leaf width (we ), the latter being a more direct indicator of boundary layer thickness. Normalized difference of margin complexity had no or weak effects on thermal dynamics, but we strongly predicted and T, whereas leaf area influenced Trange . Unlike artificial leaves, however, spatial temperature distribution in large leaves appeared to be governed largely by structural variation. Therefore, we agree that small size, specifically we , has adaptive value in hot environments but not with the idea that thermal regulation is the primary evolutionary driver of leaf dissection.
Watson, D.M., Milner, K.V. & Leigh, A. 2017, 'Novel application of species richness estimators to predict the host range of parasites.', International journal for parasitology, vol. 47, no. 1, pp. 31-39.View/Download from: UTS OPUS or Publisher's site
Host range is a critical life history trait of parasites, influencing prevalence, virulence and ultimately determining their distributional extent. Current approaches to measure host range are sensitive to sampling effort, the number of known hosts increasing with more records. Here, we develop a novel application of results-based stopping rules to determine how many hosts should be sampled to yield stable estimates of the number of primary hosts within regions, then use species richness estimation to predict host ranges of parasites across their distributional ranges. We selected three mistletoe species (hemiparasitic plants in the Loranthaceae) to evaluate our approach: a strict host specialist (Amyema lucasii, dependent on a single host species), an intermediate species (Amyema quandang, dependent on hosts in one genus) and a generalist (Lysiana exocarpi, dependent on many genera across multiple families), comparing results from geographically-stratified surveys against known host lists derived from herbarium specimens. The results-based stopping rule (stop sampling bioregion once observed host richness exceeds 80% of the host richness predicted using the Abundance-based Coverage Estimator) worked well for most bioregions studied, being satisfied after three to six sampling plots (each representing 25 host trees) but was unreliable in those bioregions with high host richness or high proportions of rare hosts. Although generating stable predictions of host range with minimal variation among six estimators trialled, distribution-wide estimates fell well short of the number of hosts known from herbarium records. This mismatch, coupled with the discovery of nine previously unrecorded mistletoe-host combinations, further demonstrates the limited ecological relevance of simple host-parasite lists. By collecting estimates of host range of constrained completeness, our approach maximises sampling efficiency while generating comparable estimates of the number of primar...
Curtis, E.M., Gollan, J., Murray, B.R. & Leigh, A. 2016, 'Native microhabitats better predict tolerance to warming than latitudinal macro-climatic variables in arid-zone plants', Journal of Biogeography, vol. 43, no. 6, pp. 1156-1165.View/Download from: UTS OPUS or Publisher's site
Aim Understanding species ability to withstand heat stress is paramount for predicting their response to increasing temperatures and decreasing rainfall. Arid systems are subject to climatic extremes, where plants, being immobile, live on the frontline of climate change. Our aim was to investigate whether: (1) warming tolerance [WT = the difference between a species physiological thermal damage threshold (T50) and the maximum temperature within its distribution (Thab)] for desert plants is higher at high latitudes, as has been shown for terrestrial ectotherms, and (2) if T50 of desert plants better corresponds with broad climatic indicators or species native microhabitats.
Location The Australian Arid Lands Botanic Garden, Port Augusta, South
Methods Using chlorophyll fluorescence techniques, we measured T50 for 42 Australian arid plant species native to different microhabitats based on water availability. WT was calculated (T50 Thab) and each metric was compared against microhabitat and broad-scale climatic variables for each species.
Results T50 was unrelated to macro-scale climate or latitude, whereas WT increased for species whose distributions extend into higher latitudes, a pattern hitherto not shown for terrestrial plants. We also found that species adapted to higher water availability in their native microhabitat had significantly lower T50 and WT than species from drier microhabitats.
Main conclusions (1) Warming tolerance increased with latitude, but the strength of this relationship was related to the way WT was quantified, with Thab and latitude being linked. (2) T50 did not correlate with latitude, but both T50 and WT were strongly related to their microhabitats. Specifically, water availability is important, such that even within a desert biome, species associated with 'wetter' microhabitats, may be particularly vulnerable to heat stress. Thus, we show that local-scale patterns better capture plant physiological responses to temperatu...
Nguyen, K.Q., Cuneo, P., Cunningham, S.A., Krix, D.W., Leigh, A. & Murray, B.R. 2016, 'Ecological effects of increasing time since invasion by the exotic African olive (Olea europaea ssp. cuspidata) on leaf-litter invertebrate assemblages', Biological Invasions, vol. 18, no. 6, pp. 1689-1699.View/Download from: UTS OPUS or Publisher's site
© 2016 Springer International Publishing Switzerland Invasive African olive, Olea europaea ssp. cuspidata (Wall. ex G.Don) Cif., forms increasingly dense stands between initial and mature stages of invasion, leading to a progressive decline in native plant diversity. Here, we examined the response of leaf-litter invertebrates to increasing time since olive invasion. We compared invertebrate assemblages among early-stage olive (0–7 years since invasion, scattered olive shrubs and seedlings in native woodland), mature olive (>15 years, uniform olive stands dominated by multi-trunked trees) and uninvaded native grassy woodland habitats (both mature stands and edges) in a critically endangered ecological community of south-eastern Australia. Invertebrate species richness was significantly reduced in mature olive compared with early-stage olive and mature native woodland habitats. Species richness did not differ significantly between early-stage olive habitat and mature native woodland, demonstrating resistance in species richness to initial invasion. Invertebrate species composition of native woodlands differed significantly from both mature olive and early-stage olive habitats, demonstrating a lack of resistance in species composition to initial olive invasion. Compositional differences were principally driven by reduced abundances within Coleoptera, Hymenoptera and Polyxenida in mature olive habitat compared with mature native woodland. These changes were significantly correlated with an increase in bare ground, plant canopy cover and litter depth, and higher moisture and lower temperature within leaf litter, in mature olive habitat. Our findings show that negative ecological impacts of invasive African olive extend beyond plants to leaf-litter invertebrate assemblages and that significant impacts on invertebrate species assemblage composition occur early in the invasion process.
Leigh, A., Hill, R. & Ball, M. 2014, 'Leaf shape influences spatial variation in photosynthetic function in Lomatia tinctoria', Functional Plant Biology, vol. 41, pp. 833-842.View/Download from: UTS OPUS or Publisher's site
A relationship exists between the two-dimensional shape of leaves and their venation architecture, such that broad or broad-lobed leaves can have leaf tissue far from major veins, potentially creating stronger gradients in water potential - and associated photosynthetic function - than found across narrow counterparts. We examined the spatial patterns of photosynthetic efficiency (DF/Fm') and non-photochemical quenching (NPQ) in response to increased vapour pressure deficit (VPD) using two morphs of Lomatia tinctoria (Labill.) R.Br: those with broad-lobed and those with narrow-lobed leaves. Stomatal conductance (gs), instantaneous water use efficiency (WUE), stomatal and minor veins density also were measured. DF/Fm' decreased with stress but was higher and less spatially heterogeneous across broad than narrow lobes. The strongest depression in DF/Fm' in broad lobes was at the edges and in narrow lobes, the tips. Non-photochemical quenching was spatially more varied in broad lobes, increasing at the edges and tips. Variation in photosynthetic function could not be explained by gs, WUE or minor vein density, whereas proximity to major veins appeared to mitigate water stress at the tips only for broad lobes. Our findings indicate that the relationship between venation architecture and water delivery alone can partially explain the spatial pattern of photosynthetic function.
Curtis, E.M., Knight, C., Petrou, K. & Leigh, A. 2014, 'A comparative analysis of photosynthetic recovery from thermal stress: a desert plant case study', Oecologia, vol. 175, pp. 1051-1061.View/Download from: UTS OPUS or Publisher's site
Our understanding of the effects of heat stress on plant photosynthesis has progressed rapidly in recent years through the use of chlorophyll a fluorescence techniques. These methods frequently involve the treatment of leaves for several hours in dark conditions to estimate declines in maximum quantum yield of photsystem II (FV/FM), rarely accounting for the recovery of effective quantum yield (?F/FM') after thermally induced damage occurs. Exposure to high temperature extremes, however, can occur over minutes, rather than hours, and recent studies suggest that light influences damage recovery. Also, the current focus on agriculturally important crops may lead to assumptions about average stress responses and a poor understanding about the variation among species thermal tolerance. We present a chlorophyll a fluorescence protocol incorporating subsaturating light to address whether species thermal tolerance thresholds (T50) are related to the ability to recover from short-term heat stress in 41Australian desert species. We found that damage incurred by 15-min thermal stress events was most strongly negatively correlated with the capacity of species to recover after a stress event of 50 °C in summer. Phylogenetically independent contrast analyses revealed that basal divergences partially explain this relationship. Although T50 and recovery capacity were positively correlated, the relationship was weaker for species with high T50 values (>51 °C). Results highlight that, even within a single desert biome, species vary widely in their physiological response to high temperature stress and recovery metrics provide more comprehensive information than damage metrics alone.
Cleverly, J., Boulain, N.P., Villalobos-Vega, R., Grant, N.M., Faux, R., Wood, C., Cook, P., Yu, Q., Leigh, A. & Eamus, D. 2013, 'Dynamics of component carbon fluxes in a semi-arid Acacia woodland, central Australia', Journal of Geophysical Research: Biogeosciences, vol. 118, no. 3, pp. 1168-1185.View/Download from: UTS OPUS or Publisher's site
Vast areas in the interior of Australia are exposed to regular but infrequent periods of heavy rainfall, interspersed with long periods at high temperatures, but little is known of the carbon budget of these remote areas or how they respond to extreme precipitation. In this study, we applied three methods to partition net ecosystem photosynthesis into gross primary production (GPP) and ecosystem respiration (Re) during two years of contrasting rainfall. The first year was wet (>250 mm above average rainfall), while little precipitation fell during the second year (>100 mmbelow average). During the first year of study, rates of GPP were large (793 g C m_2 yr_1) in this semi-arid Mulga (Acacia aneura) and grass savanna due to complementary photosynthetic responses by the canopy and C4 understorey to cycles of heavy rainfall. Patterns in GPP during the summer and autumn matched those in leaf area index (LAI), photosynthetic activity, and autotrophic respiration. During the dry year, small but positive photosynthetic uptake by Mulga contributed to the neutral carbon budget (GPP / Re = 1.06 ± 0.03). Small rates of photosynthesis by evergreen Mulga when dry were supported by storage of soil moisture above a relatively shallow hardpan. Little soil organic matter (1.1%) was available to support heterotrophic respiration (Rh) without input of fresh substrate. The two largest sources of Re in this study were autotrophic respiration by the seasonal understorey and Rh through decomposition of fresh organic matter supplied by the senescent understorey.
Curtis, E.M., Leigh, A. & Rayburg, S. 2012, 'Relationships among leaf traits of Australian arid zone plants: alternative modes of thermal protection', Australian Journal Of Botany, vol. 60, no. 6, pp. 471-483.View/Download from: UTS OPUS or Publisher's site
Despite the importance of leaf traits that protect against critically high leaf temperatures, relationships among such traits have not been investigated. Further, while some leaf trait relationships are well documented across biomes, little is known about such associations within a biome. This study investigated relationships between nine leaf traits that protect leaves against excessively high temperatures in 95 Australian arid zone species. Seven morphological traits were measured: leaf area, length, width, thickness, leaf mass per area (LMA), water content, and an inverse measure of pendulousness (LP). Two spectral properties were measured: reflectance of visible and near infrared radiation. Three key findings emerged: 1) LP decreased (pendulousness increased) with leaf size and LMA, the former relationship suggesting that pendulousness affords thermal protection when leaves are large; 2) LMA increased with thickness and decreased with water content, indicating alternative means for protection through increasing thermal mass; 3) spectral reflectance increased with LMA and thickness and decreased with water content. The consistent co-variation of thermal protective traits with LMA, a trait not usually associated with thermal protection, suggests that these traits fall along the leaf economics spectrum, with leaf longevity increasing through protection not only against structural damage but also against heat stress.
Leigh, A., Sevanto, S., Ball, M.C., Close, J.D., Ellsworth, D.S., Knight, C., Nicotra, A. & Vogel, S. 2012, 'Do thick leaves avoid thermal damage in critically low wind speeds?', New Phytologist, vol. 194, no. 2, pp. 477-487.View/Download from: UTS OPUS or Publisher's site
Summary Transient lulls in air movement are rarely measured, but can cause leaf temperature to rise rapidly to critical levels. The high heat capacity of thick leaves can damp this rapid change in temperature. However, little is known about the extent to which increased leaf thickness can reduce thermal damage, or how thick leaves would need to be to have biological significance. We evaluated quantitatively the contribution of small increases in leaf thickness to the reduction in thermal damage during critically low wind speeds under desert conditions. We employed a numerical model to investigate the effect of thickness relative to transpiration, absorptance and leaf size on damage avoidance. We used measured traits and thermotolerance thresholds of real leaves to calculate the leaf temperature response to naturally occurring variable low wind speed. Our results demonstrated that an increase in thickness of only fractions of a millimetre can prevent excursions to damaging high temperatures. This damping effect of increased thickness was greatest when other means of reducing leaf temperature (transpiration, reflectance or reduced size) were lacking. For perennial desert flora, we propose that increased leaf thickness is important in decreasing the incidence of extreme heat stress and, in some species, in enhancing long-term survival.
Leigh, A., Zwieniecki, M.A., Rockwell, F.E., Boyce, C.K., Nicotra, A. & Holbrook, N.M. 2011, 'Structural and hydraulic correlates of heterophylly in Ginkgo biloba', New Phytologist, vol. 189, no. 2, pp. 459-470.View/Download from: UTS OPUS or Publisher's site
Summary This study investigates the functional significance of heterophylly in Ginkgo biloba, where leaves borne on short shoots are ontogenetically distinct from those on long shoots. Short shoots are compact, with minimal internodal elongation; their leaves are supplied with water through mature branches. Long shoots extend the canopy and have significant internodal elongation; their expanding leaves receive water from a shoot that is itself maturing. â¢ Morphology, stomatal traits, hydraulic architecture, Huber values, water transport efficiency, in situ gas exchange and laboratory-based steady-state hydraulic conductance were examined for each leaf type. â¢ Both structure and physiology differed markedly between the two leaf types. Short-shoot leaves were thinner and had higher vein density, lower stomatal pore index, smaller bundle sheath extensions and lower hydraulic conductance than long-shoot leaves. Long shoots had lower xylem area : leaf area ratios than short shoots during leaf expansion, but this ratio was reversed at shoot maturity. Longshoot leaves had higher rates of photosynthesis, stomatal conductance and transpiration than short-shoot leaves. â¢ We propose that structural differences between the two G. biloba leaf types reflect greater hydraulic limitation of long-shoot leaves during expansion. In turn, differences in physiological performance of short- and long-shoot leaves correspond to their distinct ontogeny and architecture.
Nicotra, A., Leigh, A., Boyce, C.K., Jones, C.S., Niklas, K.J., Royer, D.L. & Tsukaya, H. 2011, 'The evolution and functional significance of leaf shape in the angiosperms', Functional Plant Biology, vol. 38, pp. 535-552.View/Download from: UTS OPUS or Publisher's site
Angiosperm leaves manifest a remarkable diversity of shapes that range from developmental sequences within a shoot and within crown response to microenvironment to variation among species within and between communities and among orders or families. It is generally assumed that because photosynthetic leaves are critical to plant growth and survival, variation in their shape reflects natural selection operating on function. Several non-mutually exclusive theories have been proposed to explain leaf shape diversity. These include: thermoregulation of leaves especially in arid and hot environments, hydraulic constraints, patterns of leaf expansion in deciduous species, biomechanical constraints, adaptations to avoid herbivory, adaptations to optimise light interception and even that leaf shape variation is a response to selection on flower form. However, the relative importance, or likelihood, of each of these factors is unclear. Here we review the evolutionary context of leaf shape diversification, discuss the proximal mechanisms that generate the diversity in extant systems, and consider the evidence for each the above hypotheses in the context of the functional significance of leaf shape. The synthesis of these broad ranging areas helps to identify points of conceptual convergence for ongoing discussion and integrated directions for future research.
Summerhayes, S.A., Bishop, M., Leigh, A. & Kelaher, B.P. 2009, 'Effects of oyster death and shell disarticulation on associated communities of epibiota', Journal of Experimental Marine Biology and Ecology, vol. 379, no. 1-2, pp. 60-67.View/Download from: UTS OPUS or Publisher's site
Oyster mortality and subsequent degradation of shell matrices may influence associated epibiota by modifying processes of filtration and biodeposition and by changing habitat structure. In the Hawkesbury River, NSW, Australia, QX disease devastated aquaculture populations of the native Sydney rock oyster, Saccostrea glomerata, and threatened wild populations. To ascertain effects of this oyster mortality on associated epibiota, we compared epifaunal communities occupying 100% oyster shell cover among 5 sites along the estuary, ranging from 25 ppt salinity and live oyster density of 96 ± 13 m- 2, to 32 ppt salinity and live oyster density of 3187 ± 233 m- 2. Epifaunal richness was greatest closest to the estuarine mouth, where live oyster abundance was greatest. Epifaunal abundance, by contrast, generally increased with distance upstream, as oyster matrices were increasingly dominated by the shells of dead oysters. To ascertain the role of live and dead oysters as habitat providers, we carried out a manipulative experiment to test the hypothesis that the epifaunal assemblages that settle over a 4 month period will significantly differ among constructed matrices comprised of live, whole dead and/or degraded (single valve) oysters. Treatments containing a component of single valves, which increase the availability of interstitial spaces and provide greater surface area for attachment, supported the greatest numbers of epibiota. Matrices comprised solely of live oysters supported fewest species and numbers of organisms. Results demonstrate that death and degradation of oysters alter the structure of associated communities, even where 100% cover of shell matrix is maintained. These results have important ramifications for management strategies and retaining estuarine biodiversity in the event that disease such as QX causes local oyster extinctions.
Carpenter, R.J., Jordan, G.J., Leigh, A. & Brodribb, T.J. 2007, 'Giant cuticular pores in Eidothea zoexylocarya (Proteaceae) leaves', American Journal of Botany, vol. 94, no. 8, pp. 1282-1288.View/Download from: UTS OPUS or Publisher's site
Ubiquitous, large diameter pores have not previously been adequately demonstrated to occur in leaf cuticles. Here we show conclusively that such structures occur in Eidothea zoexylocarya, a rainforest tree species of Proteaceae restricted to the Australian Wet Tropics. The pores are abundant, large-diameter apertures (~1 µm), that extend perpendicularly most of the way through the cuticle from the inside. They occur on both sides of the leaf, but are absent from the cuticle associated with stomatal complexes on the abaxial side. No such pores were found in any other species, including the only other species of Eidothea, E. hardeniana from New South Wales, and other species that have previously been purported to possess cuticular pores. To determine whether these pores made the cuticles more leaky to water vapor, we measured astomatous cuticular conductances to water vapor for E. zoexylocarya and seven other Proteaceae species of the Wet Tropics. Cuticular conductance for E. zoexylocarya was relatively low, indicating that the prominent pores do not increase conductance. The function of the pores is currently obscure, but the presence of both pores and an adaxial hypodermis in E. zoexylocarya but not E. hardeniana suggests evolution in response to greater environmental stresses in the tropics.
Leigh, A., Close, J.D., Ball, M.C., Siebke, K. & Nicotra, A. 2006, 'Leaf cooling curves: measuring leaf temperatures in sunlight', Functional Plant Biology, vol. 33, no. 5, pp. 515-519.View/Download from: UTS OPUS or Publisher's site
Despite the obvious benefits of using thermography under field conditions, most infrared studies at the leaf level are generally conducted in the laboratory. One reason for this bias is that accuracy can potentially be compromised in sunlight because reflected radiation from the leaf might affect the calculation of the temperature measurement. We have developed a method for measuring leaf temperature in sunlight by using thermal imagery to generate cooling curves from which the time constant for cooling, ?, can be calculated. The original temperature of the sunlit leaf may be determined by extrapolating backwards in time. In the absence of specular reflection, there is close agreement between the extrapolated sunlit temperature and the sunlit temperature recorded by the camera. However, when reflected radiation is high, the difference between the initial (incorrect) temperature determined from the sunlit image and the temperature extrapolated from the cooling curve can be > 2°C. Notably, our results demonstrate a close agreement between the extrapolated sunlit temperature and the temperature of the leaf approximately 1 s after being shaded, suggesting that this shaded image provides a good estimate of the original sunlit temperature. Thus, our technique provides two means for measuring leaf surface temperature in sunlight
Leigh, A., Cosgrove, M.J. & Nicotra, A. 2006, 'Reproductive allocation in a gender dimorphic shrub: anomalous female investment in Gynatrix pulchella?', Journal of Ecology, vol. 94, no. 6, pp. 1261-1271.View/Download from: UTS OPUS or Publisher's site
1 In gender dimorphic species, reproductive allocation (RA, the ratio of reproductive to vegetative biomass) is predicted to be greater in female plants than in male plants. Empirical research on dimorphic plant species supports this hypothesis. To date, of 44 dimorphic angiosperms for which RA has been reported in the literature, RA is greater in females than males in 40 species, is equal in four, and in no species is it greater in males. 2 In many instances where differential RA occurs, sexual dimorphism in morphological or physiological traits has been reported. This dimorphism is often attributed to the differing costs of reproduction or to selection to counteract such costs. 3 We investigated RA and other morphological and physiological characters in Gynatrix pulchella, a dimorphic species that we found ranges from dioecious to subdioecious or gynodioecious, depending on season and locality. Our results showed that contrary to our predictions functionally male plants allocated significantly more biomass to reproduction than female plants across three populations. Greater male RA was due to a combination of larger, more numerous flowers and lower leaf biomass per branch than females. 4 There were no detectable costs of greater RA in males in terms of decreased overall growth or increased mortality. Additionally, leaf nitrogen content was greater in males than in females and there were no between-sex differences in gas exchange. 5 The finding that male plants allocate significantly more resources to reproduction than females in G. pulchella is apparently a unique case.
Zwieniecki, M.A., Stone, H.A., Leigh, A., Boyce, C.K. & Holbrook, N.M. 2006, 'Hydraulic design of pine needles: one-dimensional optimization for single-vein leaves', Plant Cell and Environment, vol. 29, no. 5, pp. 803-809.View/Download from: UTS OPUS or Publisher's site
Single-vein leaves have the simplest hydraulic design possible, yet even this linear water delivery system can be modulated to improve physiological performance. We determined the optimal distribution of transport capacity that minimizes pressure drop per given investment in xylem permeability along the needle for a given length without a change in total water delivery, or maximizes needle length for a given pressure difference between petiole and needle tip. This theory was tested by comparative analysis of the hydraulic design of three pine species that differ in the length of their needles [ Pinus palustris (Engl.) Miller, ¡« 50 cm; Pinus ponderosa Lawson & Lawson, ¡« 20 cm and Pinus rigida Miller, ¡« 5 cm]. In all three species, the distribution of hydraulic permeability was similar to that predicted by the optimum solution. The needles of P. palustris showed an almost perfect match between predicted and actual hydraulic optimum solution, providing evidence that vein design is a significant factor in the hydraulic design of pine leaves.
Leigh, A. & Nicotra, A. 2003, 'Sexual dimorphism in reproductive allocation and water use efficiency in Maireana pyramidata (Chenopodiaceae), a dioecious, semi-arid shrub', Australian Journal Of Botany, vol. 51, no. 5, pp. 509-514.View/Download from: UTS OPUS or Publisher's site
Sexual dimorphism in dioecious plant species is widely attributed to the differential impacts of reproduction on male v. female plants. We investigated sexual dimorphism in reproductive, morphological and physiological traits of Maireana pyramidata (Benth.) Paul G.Wilson (Chenopodiaceae), a dioecious, semi-arid shrub endemic to Australia. We estimated reproductive allocation for each sex by calculating the relative biomass allocated to flowers and fruits per gram of leaf tissue, based on one branch per sample plant. Morphological measurements included leaf mass, stem mass, specific leaf area, plant height and plant leaf area index. We also measured leaf nitrogen and chlorophyll, gas exchange and ?13C. Reproductive allocation was nine times greater in females than in males. No significant difference between the sexes in photosynthetic rate or transpiration could be detected but instantaneous water use efficiency (photosynthesis/transpiration) was significantly lower in females than in males during the fruiting period. ?13C did not differ between the sexes. The results indicate that greater reproductive allocation in females has an immediate impact on their capacity for conservative water use but does not lead to long-term differences in water use efficiency.
Davila, Y.C., Griffiths, N. & Leigh, A. 2016, 'A blended learning approach to supporting student learning of scientific writing skills with an embedded Academic Integrity Module', Higher Education Research and Development Society of Australasia, Fremantle.View/Download from: UTS OPUS
Davila, Y.C., Griffiths, N. & Leigh, A. 2015, 'AIM for change: Supporting first year learning of best practice in scientific writing with a flipped, embedded academic integrity module', ISSOTL, The 12th Annual Conference of the International Society for the Scholarship of Teaching and Learning, Melbourne, pp. 227-228.View/Download from: UTS OPUS
Scientific writing is a fundamental professional skill but remains a daunting task for the trainee scientist. Understanding, synthesising and integrating research are essential scientific writing skills; however, appropriate use of the literature continues to be problematic with many
students accidentally plagiarising because they lack paraphrasing and citation skills . Materials to support students in developing these skills tend to be decontextualised, generic, and even ignored if they simply inform students about what plagiarism is without providing opportunities for hands-on training . Furthermore, appropriate use of literature varies within professional disciplines, causing potential confusion if learned outside a given course of study. As writing scientific reports accounts for a substantial proportion of most undergraduate science assessments, discipline specific academic literacy resources must be embedded early in the science curriculum. Such resources enhance
student learning, build confidence and support the development of competent, employable science graduates. Integrating discipline-specific resources requires disciplinary experts to re-evaluate curriculum
design and teaching practice. At our university, this re-evaluation is encouraged through both institutionally driven and grassroots level initiatives. For example, the university promotes the embedding of First Year curriculum principles  into subject design for a scaffolded transition to university learning and has implemented the First Year Experience project, in which small interdisciplinary teams embark on curriculum change and share their findings at faculty-developed Communities of Practice. These initiatives supported our project on embedding an interactive online Academic Integrity Module (AIM) on academic literacy and professional skills in scientific writing in a first year core subject. By blending out-of-classroom exercises (flipped learning approach) with workshops incorpora...
Davila, Y.C., Griffiths, N. & Leigh, A. 2015, 'Supporting first year learning of scientific writing skills with a flipped embedded academic integrity module', Proceedings of the Australian Conference on Science and Mathematics Education, Australian Conference on Science and Mathematics Education, Curtin University, pp. 21-22.View/Download from: UTS OPUS
Dylke, E.S., Ward, L.C., Stannard, C., Leigh, A. & Kilbreath, S.L. 2013, 'Bioimpedance for the spot measurement of tissue density', Journal of Physics: Conference Series.View/Download from: Publisher's site
Long-standing lymphoedema is characterised by tissues changes which are currently not detectable using bioimpedance spectroscopy. It has been suggested that a combination of bipolar and tetrapolar measurements may be used to detect these tissues changes for a single site in the transverse direction. This was technique was trialled in a group of control participants with no history of lymphoedema or recent upper limb trauma. Repeated spot measurements were done without removal of electrodes to determine biological variability as well as with removal of electrodes to determine technical reproducibility. The inter-limb spot ratio of the controls was then compared to that of a number of women previously diagnosed with secondary lymphoedema in the forearm. Biological variability was not found to greatly influence repeated measures but only moderate technical reliability was found despite excellent co-efficient of variation for the majority of the measurements. A difference was seen between those with more severe swelling and the controls. This novel technique shows promise in detecting tissue changes associated with long-standing lymphoedema.
Cook, A., Rayburg, S.C., Capon, S.J. & Leigh, A. 2011, 'Variation in seedling emergence and mortality amongst key habitat types in a semi-arid floodplain-wetland complex', Balance and Uncertainty Water in a Changing World, Proceedings of the 34th IAHR World Congress, Engineers Australia, Congress of IAHR, the International Association of Hydro-Environment Engineering and Research, IAHR, Brisbane, pp. 3044-3051.View/Download from: UTS OPUS
The presence of water in semi-arid environments is both spatially and temporally unpredictable and variable, creating a harsh and patchy environment. When present, water stimulates the germination and growth of plants but can also result in plant (or seedling) mortality. This study investigates how seedling emergence and mortality differ between various key habitats in a semi-arid floodplain wetland complex that are characterised by contrasting wetting regimes. Sediment samples were collected from five habitats (red soils, box-hollows, riparian areas, floodplains and lakes) and used in a germination experiment. Over a 12 week period, each habitat (except lakes) showed a peak in seedling emergence in the second week after initial experimental wetting, with boxhollows showing the largest emergence response in all weeks and riparian areas showing the lowest mortality (as a percent of emerged plants). Meanwhile the lowest overall emergence occurred in lakes and the highest mortality was found in red soils. Each habitat displayed a unique emergence and mortality response over the 12 weeks of the experiment suggesting that habitat has a strong influence on seedling emergence and survivability.
Leigh, A. 2012, 'Experiencing the Landscape: essential training for environmental scientists', The Conversation.
Article about field-based learning in environmental science at UTS