Margaret Barbour

Margaret Barbour
The University of Sydney · Sydney Institute of Agriculture

PhD

About

102
Publications
28,029
Reads
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7,308
Citations
Citations since 2017
3 Research Items
3571 Citations
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20172018201920202021202220230100200300400500600
20172018201920202021202220230100200300400500600
20172018201920202021202220230100200300400500600
Additional affiliations
January 2010 - January 2017
The University of Sydney
Position
  • Professor of Plant Physiology
January 2010 - present
The University of Sydney
Position
  • Professor of Plant Physiology

Publications

Publications (102)
Article
Improving our understanding of drought tolerance of crops is essential in light of future predicted changes in rainfall, decreased groundwater availability, and increasing temperatures. With a focus on above ground traits, significant improvements in drought tolerance of plants has occurred. With such gains plateauing, we have sought to quantify th...
Article
Full-text available
Contents I. II. III. IV. V. VI. VII. VIII. References SUMMARY: It has been 75 yr since leaf respiratory metabolism in the light (day respiration) was identified as a low-flux metabolic pathway that accompanies photosynthesis. In principle, it provides carbon backbones for nitrogen assimilation and evolves CO2 and thus impacts on plant carbon and ni...
Article
Full-text available
One of the longest Southern Hemisphere tree ring chronologies that has potential to provide past climate reconstructions has been produced using New Zealand kauri (Agathis australis). Work to date on kauri has been limited to reconstructions from whole-ring width analysis. In this study, we present the first replicated stable oxygen isotopic compos...
Article
Stomata represent one resistor in a series of resistances for carbon and water exchange between the leaf and the atmosphere; the remaining resistors occurring within the leaf, commonly represented as mesophyll conductance to CO2, gm, and leaf hydraulic conductance, kLeaf. Recent studies have proposed that gm and kLeaf may be coordinated across spec...
Article
How water moves through leaves, and where the phase change from liquid to vapour occurs within leaves, remain largely mysterious. Some time ago we suggested that the stable isotope composition of leaf water may contain information on transport pathways beyond the xylem, through differences in the development of gradients in enrichment within the va...
Article
I. II. III. IV. V. VI. VII. References SUMMARY: The balance of carbon dioxide (CO2 ) and water vapour exchange between leaves and the atmosphere is strongly controlled by stomatal conductance. However, the influence of transport processes within leaves has recently been gaining prominence. Stable isotope techniques are at the forefront of understan...
Article
Full-text available
Eucalyptus regnans grows rapidly from seed after wildfires, out-competing other species, thereby forming pure stands of mature forests that rank amongst the world's most carbon dense. By global standards, these forests grow on infertile soils. It is unclear how E. regnans is able to obtain large amounts nitrogen (N) from these infertile soils to su...
Article
The process of evaporation results in the fractionation of water isotopes such that the lighter (16) O isotope preferentially escapes the gas phase leaving the heavier (18) O isotope to accumulate at the sites of evaporation. This applies to transpiration from a leaf with the degree of fractionation dependent on a number of environmental and physio...
Article
One of the longest Southern Hemisphere tree ring chronologies that has potential to provide past climate reconstructions has been produced using New Zealand kauri (Agathis australis). Work to date on kauri has been limited to reconstructions from whole-ring width analysis. In this study, we present the first replicated stable oxygen isotopic compos...
Article
The oxygen isotope composition of leaf water imparts a signal to a range of molecules in the atmosphere and biosphere, but has been notoriously difficult to measure in studies requiring a large number of samples as a consequence of the labour-intensive extraction step. We tested a method of direct equilibration of water in fresh leaf samples with C...
Article
Increased mesophyll conductance (gm) has been suggested as a target for selection for high productivity and high water-use efficiency in crop plants, and genotypic variability in gm has been reported in several important crop species. However, effective selection requires an understanding of how gm varies with growth conditions, to ensure that the...
Article
Mesophyll conductance significantly, and variably, limits photosynthesis but we currently have no reliable method of measurement for C4 plants. An online oxygen isotope technique was developed to allow quantification of mesophyll conductance in C4 plants and to provide an alternative estimate in C3 plants. The technique is compared to an establishe...
Article
Full-text available
Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals inco...
Article
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Rising atmospheric [CO2] is associated with increased air temperature, and this warming may drive many rare plant species to extinction. However, to date, studies on the interactive effects of rising [CO2] and warming have focussed on just a few widely distributed plant species. Wollemi pine (Wollemia nobilis W.G.Jones, K.D.Hill, & J.M.Allen), form...
Article
Full-text available
The combined use of a gas-exchange system and laser-based isotope measurement is a tool of growing interest in plant ecophysiological studies, owing to its relevance for assessing isotopic variability in leaf water and/or transpiration under non-steady state (NSS) conditions. However, the current Farquhar & Cernusak (F&C) NSS leaf water model, orig...
Article
The two-pool and Péclet effect models represent two theories describing mechanistic controls underlying leaf water oxygen isotope composition at the whole-leaf level (δ18OL).To test these models, we used a laser spectrometer coupled to a gas-exchange cuvette to make online measurements of δ18O of transpiration (δ18Otrans) and transpiration rate (E)...
Article
Full-text available
Stable oxygen isotope techniques may be a useful tool to investigate the pathways of water movement within leaves. However, implementation of such methods is limited due to uncertainty in the effective path length (L) for the Péclet effect in leaf water enrichment models. Previous studies have found relationships between L and physiological paramet...
Article
Full-text available
Leaf hydraulic conductance (k leaf) is a central element in the regulation of leaf water balance but the properties of k leaf remain uncertain. Here, the evidence for the following two models for k leaf in well-hydrated plants is evaluated: (i) k leaf is constant or (ii) k leaf increases as transpiration rate (E) increases. The difference between s...
Conference Paper
Full-text available
The rising atmospheric CO2 concentration is altering global temperature and precipitation patterns, which could challenge agricultural productivity. Mesophyll conductance (gm) is now recognized as an important limiting process for photosynthesis and has been found to respond to both environmental conditions and leaf anatomical traits. To understand...
Article
Positive relationships between temperature and soil respiration rate are widely observed, but it remains unclear if the relationships are due to increases in soil organic matter mineralisation (R (om) ), or in root and rhizosphere respiration (R (roots) ), or increases in both. This study aims to determine the relative sensitivity of R (om) and R (...
Article
Full-text available
Earth’s atmospheric CO2 concentration (ca) for the Phanerozoic Eon is estimated from proxies and geochemical carbon cycle models. Most estimates come with large, sometimes unbounded uncertainty. Here, we calculate tightly constrained estimates of ca using a universal equation for leaf gas exchange, with key variables obtained directly from the carb...
Conference Paper
Full-text available
Understanding the effect of leaf age on photosynthetic capacity is necessary to estimate the long-term carbon budget of the leaf and the whole plant. Mesophyll conductance (gm) influences photosynthetic rate and leaf intrinsic water-use efficiency (A/gsw), and has been found to respond with environmental conditions and leaf anatomical traits. To un...
Article
Full-text available
CO2 diffusion from substomatal intercellular cavities to sites of carboxylation in chloroplasts (mesophyll conductance; g(m)) limits photosynthetic rate and influences leaf intrinsic water-use efficiency (A/g(sw)). We investigated genotypic variability of g(m) and effects of g(m) on A/g(sw) among eleven wheat (Triticum aestivum L.) genotypes under...
Article
Certainty regarding the degree to which organic molecules exchange oxygen with local water during plant cellulose synthesis (pex ) is necessary for cellulose oxygen isotope (δ(18) Ocell ) based applications in environmental and ecological studies. However, the currently accepted notion that pex is a constant of ca. 0.42 appears inconsistent with bi...
Article
Full-text available
Earth’s atmospheric CO2 concentration (ca) for the Phanerozoic Eon is estimated from proxies and geochemical carbon cycle models. Most estimates come with large, sometimes unbounded uncertainty. Here, we calculate tightly constrained estimates of ca using a universal equation for leaf gas exchange, with key variables obtained directly from the carb...
Article
High nocturnal transpiration rates (5-15% of total water loss in terrestrial plants) may be adaptive under limited fertility, by increasing nutrient uptake or transport via transpiration-induced mass flow, but the response of stomata in the dark to environmental variables is poorly understood. Here we tested the impact of soil phosphorous (P) conce...
Conference Paper
Full-text available
CO2 partial pressure at the sites of carboxylation inside the chloroplast depends in part on the conductance of CO2 diffusion from sub-stomatal intercellular cavities, termed mesophyll conductance (gm). gm influences photosynthetic rate and leaf intrinsic water-use efficiency, and has been found to respond to environmental conditions in both the sh...
Article
Full-text available
The oxygen stable isotope composition of plant organic matter (OM) (particularly of wood and cellulose in the tree ring archive) is valuable in studies of plant–climate interaction, but there is a lack of information on the transfer of the isotope signal from the leaf to heterotrophic tissues. We studied the oxygen isotopic composition and its enr...
Data
Notes S1 Evaporative enrichment models: steady-state isotopic enrichment of 18O over source water at the site of evaporation in the leaf (Δ18Oes) under steady-state conditions, steady-state isotopic enrichment of mean lamina mesophyll water (Δ18OLs) taking into account the the P’eclet effect and nonsteady-state enrichment of mean lamina mesophyll w...
Article
Full-text available
A key objective for sustainable agriculture and forestry is to breed plants with both high carbon gain and water-use efficiency (WUE). At the level of leaf physiology, this implies increasing net photosynthesis (A N) relative to stomatal conductance (g s). Here, we review evidence for CO2 diffusional constraints on photosynthesis and WUE. Analyzing...
Article
Full-text available
During daylight hours the isotope composition of leaf water generally approximates steady-state leaf water isotope enrichment model predictions. However, until very recently there was little direct confirmation that isotopic steady-state (ISS) transpiration in fact exists. Using isotope ratio infrared spectroscopy (IRIS) and leaf gas exchange syste...
Article
Full-text available
1 I. 2 II. 2 III. 4 IV. 5 V. 7 VI. 11 VII. 12 13 References 13 SUMMARY: The rate of CO(2) assimilation by plants is directly influenced by the concentration of CO(2) in the atmosphere, c(a) . As an environmental variable, c(a) also has a unique global and historic significance. Although relatively stable and uniform in the short term, global c(a) h...
Article
Full-text available
Stable oxygen isotope ratio of leaf water (δ(18) O(L) ) yields valuable information on many aspects of plant-environment interactions. However, current understanding of the mechanistic controls on δ(18) O(L) does not provide complete characterization of effective pathlength (L) of the Péclet effect, - a key component of the leaf water model. In thi...
Article
Full-text available
Mesophyll diffusion conductance to CO(2) is a key photosynthetic trait that has been studied intensively in the past years. The intention of the present review is to update knowledge of g(m), and highlight the important unknown and controversial aspects that require future work. The photosynthetic limitation imposed by mesophyll conductance is larg...
Article
Full-text available
New Zealand treeline species have low frost tolerance compared to their northern hemisphere counterparts, and appear susceptible to out-of-season frosts. However, foliage from high altitude trees is rarely directly measured. This study compares seasonal frost tolerance of mature treeline trees with local temperatures to assess whether frost affects...
Article
Although there is now a considerable literature on the inhibition of leaf respiration (CO(2) evolution) by light, little is known about the effect of other environmental conditions on day respiratory metabolism. In particular, CO(2) and O(2) mole fractions are assumed to cause changes in the tricarboxylic acid pathway (TCAP) but the amplitude and e...
Article
The idea that photosynthesis-weighted tree canopy leaf temperature (T(canδ)) can be resolved through analysis of oxygen isotope composition in tree wood cellulose (δ(18) O(wc)) has led to the observation of boreal-to-subtropical convergence of T(canδ) to c. 20°C. To further assess the validity of the large-scale convergence of T(canδ), we used the...
Article
Carbon and oxygen isotope discrimination of CO2 during photosynthesis (Δ13Cobs and Δ18Oobs) were measured along a monocot leaf, triticale (Triticum × Secale). Both Δ13Cobs and Δ18Oobs increased towards the leaf tip. While this was expected for Δ18Oobs, because of progressive enrichment of leaf water associated with the Péclet effect, the result was...
Article
Patterns in the natural abundance of nitrogen (N) isotopes (¹⁵N and ¹⁴N) can help in the understanding of ecosystem processes along environmental gradients, because some processes fractionate against the heavier isotope. We measured δ¹⁵N in many components of the Franz Josef soil chronosequence in New Zealand to see how each component varied along...
Article
Leaf intrinsic water-use efficiency (WUE), the ratio of photosynthetic rate to stomatal conductance (A/g(s) ), is a key plant trait linking terrestrial carbon and water cycles. A rapid, integrative proxy for A/g(s) is of benefit to crop breeding programmes aiming to improve WUE, but also for ecologists interested in plant carbon-water balance in na...
Article
Full-text available
Mesophyll conductance, gm, was estimated from measurements of stomatal conductance to carbon dioxide transfer, gs, photosynthesis, A, and chlorophyll fluorescence for Year 0 (current-year) and Year 1 (1-year-old) fully sunlit leaves from short (2 m tall, 10-year-old) and tall (15 m tall, 120-year-old) Nothofagus solandrii var. cliffortiodes trees g...
Article
1. Many grasslands worldwide are undergoing succession to woody vegetation, causing complex effects on carbon (C) sequestration, nutrient cycling and biodiversity. Land managers are frequently tasked with maximizing ecosystem services and biodiversity. Nonetheless, there are few studies quantifying trade-offs between ecosystem services and biodiver...
Article
The CO₂ respired by darkened, light-adapted, leaves is enriched in ¹³C during the first minutes, and this effect may be related to rapid changes in leaf respiratory biochemistry upon darkening. We hypothesized that this effect would be evident at the ecosystem scale. High temporal resolution measurements of the carbon isotope composition of ecosyst...
Article
Carbon and oxygen isotope discrimination of CO2 during photosynthesis (Δ13C obs and Δ18O obs) were measured along a monocot leaf, triticale (Triticum × Secale). Both Δ13C obs and Δ18O obs increased towards the leaf tip. While this was expected for Δ18O obs, because of progressive enrichment of leaf water associated with the Péclet effect, the resul...
Article
Full-text available
Despite abundant literature, the predicted response of soil respiration (R S) to soil temperature (T S) remains uncertain. We aimed to quantify the temperature dependency of soil respired CO2 derived from organic matter (R OM), and investigated the relationship between the R OM responses to temperature, soil properties, and vegetation, using a natu...
Article
Stable oxygen isotope ratios in tree wood cellulose have recently been demonstrated as a useful tool to investigate tree leaf temperature patterns in relation to carbon uptake. Using an improved version of the tree cellulose oxygen isotope model, we calculated tree leaf temperatures from two published datasets of oxygen isotope ratios of tree wood...
Article
Full-text available
PROtocols, METHods, Explanations and Updated Standards Wiki (PrometheusWiki, http://www.publish.csiro.au/prometheuswiki/) is a new open access, fully searchable web resource that contains protocols and methods for plant physiology, ecology and environmental sciences. Contributions can be uploaded by anyone in the community, with attributed authorsh...
Conference Paper
Background/Question/Methods Transitions between arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) vegetation are a common occurrence in land management, natural succession, and following species invasions, yet our understanding of the effects of such mycorrhizal status transitions on ecosystem outcomes is severely limited. Here we address the q...
Article
Quantifying the loss of soil carbon through respiration has proved difficult, due to the challenge of measuring the losses associated with the turnover of soil organic matter (SOM) as distinct from autotrophic components. In forest ecosystems the δ13C value of respiration from turnover of SOM (δ13CRSOM) is typically 2–4‰ enriched compared with that...
Conference Paper
With the bulk of ecosystem carbon stored below-ground, terrestrial ecosystems may become a net source of carbon if rising soil temperatures cause previously recalcitrant soil carbon to be metabolized by soil microbes and released to the atmosphere as CO2. Soil respiration rate increases dramatically with temperature, so long as soil water content i...
Article
Leaf internal, or mesophyll, conductance to CO(2) (g(m)) is a significant and variable limitation of photosynthesis that also affects leaf transpiration efficiency (TE). Genotypic variation in g(m) and the effect of g(m) on TE were assessed in six barley genotypes (four Hordeum vulgare and two H. bulbosum). Significant variation in g(m) was found b...
Article
Full-text available
Improved global estimates of terrestrial photosynthesis and respiration are critical for predicting the rate of change in atmospheric CO(2). The oxygen isotopic composition of atmospheric CO(2) can be used to estimate these fluxes because oxygen isotopic exchange between CO(2) and water creates distinct isotopic flux signatures. The enzyme carbonic...
Article
Full-text available
The carbon and oxygen stable isotope composition of wood cellulose (delta(13)C(cellulose) and delta(18)O(cellulose), respectively) reveal well-defined seasonal variations that contain valuable records of past climate, leaf gas exchange and carbon allocation dynamics within the trees. Here, we present a single-substrate model for wood growth to inte...
Article
Full-text available
Non-photosynthetic, or heterotrophic, tissues in C 3 plants tend to be enriched in 13 C compared with the leaves that supply them with photosynthate. This isotopic pattern has been observed for woody stems, roots, seeds and fruits, emerging leaves, and parasitic plants incapable of net CO 2 fixation. Unlike in C 3 plants, roots of herbaceous C 4 pl...
Article
Full-text available
Stable isotopes of atmospheric carbon dioxide (CO2) contain a wealth of information regarding biosphere-atmosphere interactions. The carbon isotope ratio of CO2 (delta13Crpar reflects the terrestrial carbon cycle including processes of photosynthesis, respiration, and decomposition. The oxygen isotope ratio (delta18O) reflects terrestrial carbon an...
Article
Full-text available
High-resolution measurements of the carbon and oxygen stable isotope composition of cellulose in annual tree rings (delta13Ccellulose and delta18Ocellulose, respectively) reveal well-defined seasonal patterns that could contain valuable records of past climate and tree function. Interpreting these signals is nonetheless complex because they not onl...
Article
Stable carbon and oxygen isotope ratios of CO2 are useful tracers in studies of carbon and water cycling between the terrestrial biosphere and the atmosphere. Interpretation of variation in 13CO2 and C16O18O relies on models describing physical and biochemical processes and their associated fractionations. A layer of complexity not currently quanti...
Article
A portable photosynthesis system (Li-6400, Li-Cor, NE) and a through-flow soil chamber were used to continuously measure the gas exchange of leaf and below ground components in pots containing corn, Triticale and a non-planted control. Temperature was kept constant through-out the experiment, and measurements were made at 4 min intervals over a ful...
Article
Evidence is building that stomatal conductance to water vapour (g(s)) can be quite high in the dark in some species. However, it is unclear whether nocturnal opening reflects a mechanistic limitation (i.e. an inability to close at night) or an adaptive response (i.e. promoting water loss for reasons unrelated to carbon gain). Further, it is unclear...