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, including the links between leaf shape and leaf hydraulics (Holbrook lab, Harvard University) and leaf temperature (Nicotra lab, The Australian National University). In 2008-2011, I chaired the Leaf Temperature Working Group, Supported by the ARC Australian Vegetation Network, to investigate how leaves thermoregulate under heat stress.
My current emphasis is on how plants function and survive under high temperature extremes, which are increasing in frequency, intensity and duration. I am especially fascinated with plants living in the apparently harsh conditions of arid regions, namely high temperatures coupled with low, irregular rainfall. To validate theory, I am a strong believer in field research, where I use a range of physiological methodologies to measure plant responses to environmental extremes.
- Senior Fellow, Higher Education Academy, 2015
- Australian Government Office of Learning and Teaching Citation, 2013, for: Inspiring and motivating students in environmental science through learning approaches that highlight relevance to professional scientific practice.
- UTS Learning and Teaching Award for Early Career Teaching, 2011, for: Supporting student transition to first year and beyond through inspiring and motivating continued learning in science.
- Australian Rangelands Society, 2010-present.
- Ecological Society of Australia (ESA), 2002-present.
- ESA Equity and Diversity Committee, 2018-present.
Contribution to research community
- Associate Editor, Austral Ecology, 2013-2018
- Reviewer of scientific manuscripts: American Journal of Botany, Annals of Botany, Evolutionary Ecology, Frontiers, Global Change Biology, Journal of Arid Environments, Journal of Biogeography, Nature Plants, Nature: Scientific Reports, New Phytologist, Photosynthesis Research, Plant, Cell and Environment,The Rangeland Journal.
Can supervise: YES
My research addresses how plants survive environmental stresses, particularly in arid land systems, which cover over one third of the terrestrial land mass globally. In Australia, desert vegetation is responsible for considerable carbon capture and support a $2.5 billion grazing industry. In these regions, among the greatest stresses for plants are extreme high temperature events, which are becoming increasingly frequent and intense. Knowing how plants respond to such extremes in these already extreme environments is vital if we are to predict species distribution as the climate changes. My research is both field- and laboratory-based and I collaborate widely across the life and physical sciences, both within Australia and internationally.
Research areas include:
- Plant thermal tolerance to temperature extremes, particularly for plants living on the edge of biological tolerance in extreme environments, including responses to combined stresses.
- Leaf structure-function relationships, including leaf shape, size and other traits, particularly with respect to leaf thermodynamics.
- Plant responses to human- and animal-induced landscape modifications such as grazing and regulation of inland water systems.
Undergraduate subjects I have coordinated:
- 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 supervised research project on plant ecology (also a potential preparation for Honours or Masters).
Curtis, EM, Knight, CA & Leigh, A 2019, 'Intracanopy adjustment of leaf-level thermal tolerance is associated with microclimatic variation across the canopy of a desert tree (Acacia papyrocarpa).', Oecologia, vol. 189, no. 1, pp. 37-46.View/Download from: Publisher's site
Tree crowns are spatially heterogeneous, sometimes resulting in significant variation in microclimate across the canopy, particularly with respect to temperature. Yet it is not known whether such localised temperature variation equates to intracanopy variation in leaf-level physiological thermal tolerance. Here, we studied whether microclimate variation across the canopy of a dominant desert tree equated to localised variation in leaf thermal thresholds (T50) among four canopy positions: upper south, upper north, lower south, lower north. Principal component analysis was used to generate a composite climatic stress variable (CSTRESS) from canopy temperature, vapour pressure deficit, and relative humidity. We also determined the average number of days that maximum temperatures exceeded the air temperature equating to this species' critical threshold of 49 °C (AT49). To estimate how closely leaf temperatures track ambient temperature, we predicted the thermal time constant (τ) for leaves at each canopy position. We found that CSTRESS and AT49 were significantly greater in lower and north-facing positions in the canopy. Differences in wind speed with height resulted in significantly longer predicted τ for leaves positioned at lower, north-facing positions. Variation in these drivers was correlated with significantly higher T50 for leaves in these more environmentally stressful canopy positions. Our findings suggest that this species may optimise resources to protect against thermal damage at a whole-plant level. They also indicate that, particularly in desert environments with steep intracanopy microclimatic gradients, whole-plant carbon models could substantially under- or overestimate productivity under heat stress, depending on where in the canopy T50 is measured.
Huston, WM, Cranfield, CG, Forbes, SL & Leigh, A 2019, 'A sponsorship action plan for increasing diversity in STEMM.', Ecology and Evolution, vol. 9, no. 5, pp. 2340-2345.View/Download from: Publisher's site
There are numerous structural and cultural barriers to the progression of women and marginalized groups to leadership in academia, especially in Science, Technology, Engineering, Mathematics and Medicine (STEMM). A range of interventions have been described to address this inequity, with varying success. Here, we suggest that sponsorship could be one effective intervention and propose an institutional action plan to implement a sponsorship program in academia. We outline why sponsorship could be an effective strategy, especially if implemented through a deliberate program by an institution. We then detail the three components of an action plan to be considered in implementation: the elements of the program, the activities that sponsorship in academia likely encompasses, and the selection of sponsors and protégés. The plan could also be enacted by academic leadership in the absence of an institutional program and could serve as a guide to individuals in academia aspiring to address diversity and inclusion in STEMM.
Knight, S, Leigh, A, Davila, Y, Martin, L & Krix, D 2019, 'Calibrating Assessment Literacy Through Benchmarking Tasks', Assessment and Evaluation in Higher Education, vol. 44, no. 8, pp. 1121-1132.View/Download from: Publisher's site
In calibration tasks students assess exemplar texts using criteria against which their own work will be assessed. Typically these tasks are used in the context of training for peer assessment. Little research has been conducted on the benefits of calibration tasks, such as benchmarking, as learning opportunities in their own right. This paper examines a dataset from a long-running benchmarking task ( 500 students per semester, for four semesters). We investigate the relationship of benchmarking performance to other student outcomes, including ability to self-assess accurately. We show that students who complete the benchmarking perform better, that there is a relationship between benchmarking performance and self-assessment performance, and that students appreciate the support for learning that benchmarking tasks provide. We discuss implications for teaching and learning flagging the potential of calibration tasks as an under-explored tool.
Drake, JE, Tjoelker, MG, Varhammar, A, Medlyn, BE, Reich, PB, Leigh, A, Pfautsch, S, Blackman, CJ, Lopez, R, Aspinwall, MJ, Crous, KY, Duursma, RA, Kumarathunge, D, De Kauwe, MG, Jiang, M, Nicotra, AB, Tissue, DT, Choat, B, Atkin, OK & Barton, CVM 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: Publisher's site
Leigh, A, Sevanto, S, Close, JD & Nicotra, AB 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: 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 (τ) 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 τ 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, DM, Milner, KV & 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: Publisher's site
Nguyen, KQ, Cuneo, P, Cunningham, SA, Krix, DW, Leigh, A & Murray, BR 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: 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.
Curtis, EM, Gollan, J, Murray, BR & 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: 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...
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: 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, EM, 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: 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, NP, Villalobos-Vega, R, Grant, NM, 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: 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, EM, 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: 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, MC, Close, JD, Ellsworth, DS, 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: 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, MA, Rockwell, FE, Boyce, CK, Nicotra, A & Holbrook, NM 2011, 'Structural and hydraulic correlates of heterophylly in Ginkgo biloba', New Phytologist, vol. 189, no. 2, pp. 459-470.View/Download from: 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, CK, Jones, CS, Niklas, KJ, Royer, DL & 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: 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, SA, Bishop, M, Leigh, A & Kelaher, BP 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: 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, RJ, Jordan, GJ, Leigh, A & Brodribb, TJ 2007, 'Giant cuticular pores in Eidothea zoexylocarya (Proteaceae) leaves', American Journal of Botany, vol. 94, no. 8, pp. 1282-1288.View/Download from: 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, JD, Ball, MC, 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: 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, MJ & 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: 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, MA, Stone, HA, Leigh, A, Boyce, CK & Holbrook, NM 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: 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: 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.
Many Australian mistletoe species are cryptic, closely resembling their host foliage and overall appearance. Seed-dispersing birds have been proposed as a selective agent for host resemblance, with cryptic mistletoes only located by thoroughly searching through canopies regardless of infection status, boosting mistletoe populations by increasing the frequency of seeds dispersed to uninfected hosts; however, this idea is as yet untested. We measured bird visitation to fruiting mistletoes (n = 20) over two consecutive days, with manual defoliation of the mistletoe occurring before observation began on the second day to determine the effect of the visual appearance of the mistletoe on potential seed-dispersing birds, expecting defoliation to reduce the number of visits. Visits to the mistletoes were compared between days of observation and dietary guild (mistletoe specialist/nonspecialist). Intact mistletoes were visited more than the defoliated mistletoes, and the dietary guilds differed in their visitation patterns. This work demonstrates that the visual acuity of seed-dispersers can distinguish subtle differences in mistletoe phenotypes within infected hosts, consistent with the hypothesis that those mistletoes that more closely resemble their hosts are more difficult to perceive from afar and therefore more likely to have their seeds dispersed to uninfected hosts.
Geange, S, Arnold, P, Catling, A, Coast, O, Cook, A, Gowland, K, Leigh, A, Notarnicola, R, Posch, B, Venn, S, Zhu, L & Nicotra, A 2020, 'Plant thermal tolerance: a global synthesis for future research', EGU General Assembly 2020, Online.View/Download from: Publisher's site
Extreme temperature events are increasing in frequency and intensity across the globe. These extremes, rather than averages, drive species evolution and determine survival by profoundly changing the structure and fluidity of cell membranes, altering enzyme function, and denaturing proteins. Given not only our dependence on agricultural crops and natural vegetation, but also the role of photosynthetic processes within the carbon and hydrological cycles, it is imperative to assess the state of our understanding of the potential impacts of extreme events on plants. Scaling responses from the molecular and organ level to ecosystem function is not without challenge however. There is vast literature on plant thermal tolerance research, but the body of literature is so large, the approaches so disparate and often siloed among disciplines, that research in this field risks floundering at a critical time. We conducted a systematic review of more than 21,500 studies spanning over 100 years of research that yielded almost 1,700 included studies on the tolerance of cultivated and wild land plants to both heat and cold. Our review indicates that most studies on thermal tolerance focus on the cold tolerance of cultivated species (52%) and only a trivial percentage of studies have considered both heat and cold tolerance of any given species (~5%). Combined heat and cold tolerance are important in areas where plants are exposed to extremes of both or may be in the future. This review illustrates the global distribution and concentrations of thermal tolerance studies and the diversity of thermal tolerance methods, ranging from molecular to biochemical, physiological and physical examinations, from transgenic model plants to agricultural and horticultural crops, to natural forest trees, shrubs, and grassland herbs. Critically, it also demonstrates that methods and metrics for assessing thermal tolerance are far from standardised, such that our potential to achieve mechanistic insi...
Davila, YC, 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.
Davila, YC, 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.
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, YC, 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.
Cook, A, Rayburg, SC, Capon, SJ & 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.
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
Research collaborators include:
- The Australian Arid Lands Botanic Garden (AALBG), via a Research Collaboration Agreement with the Port Augusta City Council and the Friends of the AALBG, 2012-present.
- NSW Department of Planning, Industry and Environment (Save our Species program).
- Australian National Botanic Garden, Canberra.
- Australian Botanical Garden Mt Annan, Sydney.
- Australian National University, Research School of Biology and Research School of Physics.
- California Polytechnic State University, USA, Biological Sciences Department.
- Charles Sturt University, School of Environmental Sciences.
- Harvard University, USA, Department of Organismic and Evolutionary Biology.
- Hawkesbury Institute for the Environment, Western Sydney University.
- University of Tasmania, School of Plant Sciences.
- University of Wollongong, School of Biological Sciences.