Lucas A Cernusak

James Cook University Brisbane · College of Marine and Environmental Sciences

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...

Elevated atmospheric CO 2 concentrations (c a) will undoubtedly affect the metabolism of tropical forests worldwide; however, critical aspects of how tropical forests will respond remain largely unknown. Here, we review the current state of knowledge about physiological and ecological responses, with the aim of providing a framework that can help t...

Stable carbon isotope ratios (δ(13) C) of terrestrial plants are employed across a diverse range of applications in environmental and plant sciences; however, the kind of information that is desired from the δ(13) C signal often differs. At the extremes, it ranges between purely environmental and purely biological. Here, we review environmental dri...

Modern plant physiological theory stipulates that the resistance to water movement from plants to the atmosphere is overwhelmingly dominated by stomata. This conception necessitates a corollary assumption—that the air spaces in leaves must be nearly saturated with water vapour; that is, with a relative humidity that does not decline materially belo...

Elevated air temperature (Tair) and vapour pressure deficit (VPDair) significantly influence plant functioning, yet their relative impacts are difficult to disentangle. We examined the effects of elevated Tair (+6°C) and VPDair (+0.7 kPa) on the growth and physiology of six tropical tree species. Saplings were grown under well‐watered conditions in...

Climate change has accelerated the frequency of catastrophic wildfires; however, the drivers that control the time‐to‐recover of forests are poorly understood. We integrated remotely sensed data, climate records, and landscape features to identify the causes of variability in the time‐to‐recover of canopy leaf area in southeast Australian eucalypt...

Mesophyll conductance ( g m ) is a crucial plant trait that can significantly limit photosynthesis. Measurement of photosynthetic C ¹⁸ O ¹⁶ O discrimination (Δ ¹⁸ O) has proved to be the only viable means of resolving g m in both C 3 and C 4 plants. However, the currently available methods to exploit Δ ¹⁸ O for g m estimation are error prone due to...

Enhanced efficiency fertilizers (EEFs) can reduce nitrogen (N) losses in temperate agriculture but are less effective in the tropics. We aimed to design a new EEF and evaluate their performance in simple‐to‐complex tests with tropical soils and crops. We melt‐extruded urea at different loadings into biodegradable polymer matrix composites using bio...

The strong covariation of temperature and vapour pressure deficit (VPD) in nature limits our understanding of the direct effects of temperature on leaf gas exchange. Stable isotopes in CO2 and H2O vapour provide mechanistic insight into physiological and biochemical processes during leaf gas exchange. We conducted combined leaf gas exchange and onl...

A fundamental assumption when using hydrogen and oxygen stable isotopes to understand ecohydrological processes is that no isotope fractionation occurs during plant water uptake/transport/redistribution. A growing body of evidence has indicated that hydrogen isotope fractionation occurs in certain environments or for certain plant species. However,...

Models estimating decomposition rates of dead wood across space and time are mainly based on studies carried out in temperate zones where microbes are dominant drivers of decomposition. However, most dead wood biomass is found in tropical ecosystems, where termites are also important wood consumers. Given the dependence of microbial decomposition o...

Woody biomass is a large carbon store in terrestrial ecosystems. In calculating biomass, tree stems are assumed to be solid structures. However, decomposer agents such as microbes and insects target stem heartwood, causing internal wood decay which is poorly quantified. We investigated internal stem damage across five sites in tropical Australia al...

Tropospheric ozone (O3) is a global air pollutant that adversely affects plant growth. Whereas the impacts of O3 have previously been examined for some tropical commodity crops, no information is available for the pantropical crop, banana (Musa spp.). To address this, we exposed Australia’s major banana cultivar, Williams, to a range of [O3] in ope...

The oxygen isotope composition (δ¹⁸O) of tree‐ring cellulose is used to evaluate tree physiological responses to climate, but their interpretation is still limited due to the complexity of the isotope fractionation pathways. We assessed the relative contribution of seasonal needle and xylem water δ¹⁸O variations to the intra‐annual tree‐ring cellul...

Climate change is expected to increase the intensity and occurrence of drought in tropical regions, potentially affecting the phenology and physiology of tree species. Phenological activity may respond to a drying and warming environment by advancing reproductive timing and/or diminishing the production of flowers and fruits. These changes have the...

Atmospheric conditions are expected to become warmer and drier in the future, but little is known about how evaporative demand influences forest structure and function independently from soil moisture availability, and how fast‐response variables (such as canopy water potential and stomatal conductance) may mediate longer‐term changes in forest str...

Deadwood is an important yet understudied carbon pool in tropical ecosystems. Wood microclimate, as defined by wood moisture content and temperature, drives decomposer (microbial, termite) activities and deadwood degradation to CO2. Microclimate is strongly influenced by local climate, and thus, climate data could be used to predict CO2 fluxes from...

Oxygen and hydrogen isotopes of cellulose in plant biology are commonly used to infer environmental conditions, often from time series measurements of tree rings. However, the covariation (or the lack thereof) between δ¹⁸O and δ²H in plant cellulose is still poorly understood. We compared plant water, and leaf and branch cellulose from dominant tre...

Sugarcane is a vital commodity crop often grown in (sub)tropical regions which have been experiencing a recent deterioration in air quality. Unlike for other commodity crops, the risk of air pollution, specifically ozone (O3), to this C4 crop has not yet been quantified. Yet, recent work has highlighted both the potential risks of O3 to C4 bioenerg...

• Woody biomass is a large carbon store in terrestrial ecosystems. In calculating biomass, tree stems are assumed to be solid structures; however, decomposer agents such as microbes and insects target heartwood in stems, causing internal wood decay which is poorly quantified. • We investigated internal stem damage across five sites in tropical Aust...

The record contains information on leaf chemistry studied on co-occurring tropical mountaintop restricted tree species from various mountaintop sites in Far North Queensland in 2019. Data on leaf stable carbon and nitrogen isotope concentrations, and elemental chemistry such as carbon, nitrogen, phosphorous, calcium, magnesium, potassium, sodium, c...

The data set contains information on topsoil chemistry for 20, 10 cm deep soil cores sampled along an elevation gradient (40-1550 m a.s.l.) in Far North Queensland. Information on soil C:N, N:P and C:P ratios and soil pH and organic matter content are provided. Soil elemental composition such as calcium, potassium, phosphorus, sulfur, iron, mangane...

As the global climate warms, a key question is how increased leaf temperatures will affect tree physiology and the coupling between leaf and air temperatures in forests. To explore the impact of increasing temperatures on plant performance in open air, we warmed leaves in the canopy of two mature evergreen forests, a temperate Eucalyptus woodland a...

Variation in decay rates across woody species is a key uncertainty in predicting the fate of carbon stored in deadwood, especially in the tropics. Quantifying the relative contributions of biotic decay agents, particularly microbes and termites, under different climates and across species with diverse wood traits could help explain this variation....

We present a robust estimation of the CO2 concentration at the surface of photosynthetic mesophyll cells (cw), applicable under reasonable assumptions of assimilation distribution within the leaf. We used Capsicum annuum, Helianthus annuus and Gossypium hirsutumas model plants for our experiments. We introduce calculations to estimate cw using inde...

Elevation gradients provide natural laboratories for investigating tropical tree ecophysiology in the context of climate warming. Previously observed trends with increasing elevation include decreasing stem diameter growth rates (GR), increasing leaf mass per area (LMA), higher root-to-shoot ratios (R:S), increasing leaf δ 13 C, and decreasing leaf...

“Least‐cost theory” posits that C3 plants should balance rates of photosynthetic water loss and carboxylation in relation to the relative acquisition and maintenance costs of resources required for these activities. Here we investigated the dependency of photosynthetic traits on climate and soil properties using a new Australia‐wide trait dataset s...

Deadwood is a large global carbon store with its store size partially determined by biotic decay. Microbial wood decay rates are known to respond to changing temperature and precipitation. Termites are also important decomposers in the tropics but are less well studied. An understanding of their climate sensitivities is needed to estimate climate c...

Tropical forests take up more carbon (C) from the atmosphere per annum by photosynthesis than any other type of vegetation. Phosphorus (P) limitations to C uptake are paramount for tropical and subtropical forests around the globe. Yet the generality of photosynthesis-P relationships underlying these limitations are in question, and hence are not r...

Evidence exists that tree mortality is accelerating in some regions of the tropics1,2, with profound consequences for the future of the tropical carbon sink and the global anthropogenic carbon budget left to limit peak global warming below 2 °C. However, the mechanisms that may be driving such mortality changes and whether particular species are es...

Stomata are orifices that connect the drier atmosphere with the interconnected network of more humid air spaces that surround the cells within a leaf. Accurate values of the humidities inside the substomatal cavity, wi, and in the air, wa, are needed to estimate stomatal conductance and the CO2 concentration in the internal air spaces of leaves. Bo...

Tropical forests are some of the most biodiverse ecosystems in the world, yet their functioning is threatened by anthropogenic disturbances and climate change. Global actions to conserve tropical forests could be enhanced by having local knowledge on the forestsʼ functional diversity and functional redundancy as proxies for their capacity to respon...

Between late 2015 and early 2016, more than 7,000 ha of mangrove forest died along the coastline of the Gulf of Carpentaria, in northern Australia. This massive die-off was preceded by a strong 2015/2016 El Niño event, resulting in lower precipitation, a drop in sea level and higher than average temperatures in northern Australia. In this study, we...

Predicting species‐level responses to drought at the landscape scale is critical to reducing uncertainty in future terrestrial carbon and water cycle projections. We embedded a stomatal optimisation model in the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model and parameterised the model for 15 canopy dominant eucalypt tree s...

We compiled hydrogen and oxygen stable isotope compositions (δ²H and δ¹⁸O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ²H was more closely correlated with δ²H of xylem water or atmospheric vapour, whereas leaf water δ¹⁸O was more closely correlated with air relative humidity. This resulted from t...

In 2020, the Australian and New Zealand flux research and monitoring network, OzFlux, celebrated its 20th anniversary by reflecting on the lessons learned through two decades of ecosystem studies on global change biology. OzFlux is a network not only for ecosystem researchers, but also for those ‘next users’ of the knowledge, information and data t...

Tropical forests account for more than half of the above-ground carbon on planet earth. Changes in species and trait composition resulting from climate change may strongly influence this carbon pool and therefore the global carbon cycle. We highlight how climate change may impact forest regeneration processes in tropical wet forests by altering the...

Background and aims: Despite the critical role of woody tissues in determining net carbon exchange of terrestrial ecosystems, relatively little is known regarding the drivers of sapwood and bark respiration. Methods: Using one of the most comprehensive wood respiration datasets to date (82 species from Australian rainforest, savanna and temperat...

The far north Queensland microclimate (FNQ - microclim) is an ongoing long-term microclimate monitoring project from across five tropical rainforest sites, (Daintree Rainforest SuperSite, Cape Tribulation; Daintree Rainforest SuperSite, Cow Bay; Rex Range; Mt. Lewis National Park; Mt. Bellenden Ker), located within an elevation range of 40 - 1550 m...

Tree saplings and shrubs are frequently overlooked components of tropical rainforest biodiversity, and it may be hypothesized that their small stature and shallow root systems predisposes them to be vulnerable to drought. However, these purported influences of drought on growth, physiological performance and plant traits on tree saplings and shrubs...

Climate change is projected to increase the imbalance between the supply (precipitation) and atmospheric demand for water (i.e., increased potential evapotranspiration), stressing plants in water-limited environments. Plants may be able to offset increasing aridity because rising CO2 increases water use efficiency. CO2 fertilization has also been c...

21 Tree saplings and shrubs are frequently overlooked components of tropical rainforest 22 biodiversity, and it may be hypothesized that their small stature and shallow root systems 23 predisposes them to be vulnerable to drought. However, these purported influences of 24 drought on growth, physiological performance and plant traits have yet to be...

Tree saplings and shrubs are frequently overlooked components of tropical rainforest biodiversity, and it may be hypothesized that their small stature and shallow root systems predisposes them to be vulnerable to drought. However, these purported influences of drought on growth, physiological performance and plant traits have yet to be studied in s...

Animals, such as termites, have largely been overlooked as global-scale drivers of biogeochemical cycles 1,2 , despite site-specific findings 3,4 . Deadwood turnover, an important component of the carbon cycle, is driven by multiple decay agents. Studies have focused on temperate systems 5,6 , where microbes dominate decay ⁷ . Microbial decay is se...

The carbon atoms deposited in tree rings originate from the CO 2 in the atmosphere to which the tree’s canopy is exposed. Thus, the first control on the stable carbon-isotope composition of tree rings is by δ ¹³ C of atmospheric CO 2 . There has been an inter-annual trend of decreasing δ ¹³ C of atmospheric CO 2 over the past two centuries as a res...

Tropical tree species employ varying strategies in young leaves to minimise losses to herbivory. The young leaves of species with delayed greening are thought to be less visible to herbivores, but likely incur a cost to leaf‐level carbon gain via lower photosynthetic rates during leaf development. Increasing atmospheric CO2 concentrations may reduc...

Generalised dose–response curves are essential to understand how plants acclimate to atmospheric CO2. We carried out a meta‐analysis of 630 experiments in which C3 plants were experimentally grown at different [CO2] under relatively benign conditions, and derived dose–response curves for 85 phenotypic traits. These curves were characterised by form...

A better understanding of how climate affects growth in tree species is essential for improved predictions of forest dynamics under climate change. Long-term climate averages (mean climate) drives spatial variations in species’ baseline growth rates, whereas deviations from these averages over time (anomalies) can create growth variation around the...

This article is a Commentary on Márquez et al. (2022), 233: 156–168.

We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of per...

This scientific commentary refer to ‘Combining carbon and oxygen isotopic signatures to identify ozone-induced declines in tree water-use efficiency’ by Li et al. (doi: 10.1093/treephys/tpab041). Ozone (O3) in the troposphere is an important air pollutant that causes adverse effects on plants and ecosystems worldwide (Ainsworth et al. 2012, Grulke...

Aim Elevational gradients provide excellent opportunities to explore long-term morphological and physiological responses of plants to environmental change. We determined the difference in the elevational pattern of foliar carbon isotope composition (δ¹³C) between lianas and trees, and assessed whether this difference arises from changes in photosyn...

Increasing severity and frequency of drought is predicted for large portions of the terrestrial biosphere, with major impacts already documented in wet tropical forests. Using a four-year rainfall exclusion experiment in the Daintree Rainforest in northeast Australia, we examined canopy tree responses to reduced precipitation and soil water availab...

Climate change is projected to increase the imbalance between the supply (precipitation) and atmospheric demand for water (i.e. increased potential evapotranspiration), stressing plants in water-limited environments. Plants may be able to offset increasing aridity because rising CO2 increases water-use-efficiency. CO2 fertilization has also been ci...

A better understanding of how climate affects growth in tree species is essential for improved predictions of forest dynamics under climate change. Long-term climate averages (mean climate) and short-term deviations from these averages (anomalies) both influence tree growth, but the rarity of long-term data integrating climatic gradients with tree...

The oxygen isotope composition of atmospheric carbon dioxide (CO2) is intimately linked to large-scale variations in the cycling of CO2 and water across the Earth's surface. Understanding the role the biosphere plays in modifying the oxygen isotope composition of atmospheric CO2 is particularly important as this isotopic tracer has the potential to...

Termites are important ecosystem engineers in tropical habitats, with different feeding groups able to decompose wood, grass, litter, and soil organic matter. In most tropical regions, termite abundance and species diversity are assumed to increase with rainfall, with highest levels found in rainforests. However, in the Australian tropics, this pat...

There is huge uncertainty about how global exchanges of carbon between the atmosphere and land will respond to continuing environmental change. A better representation of photosynthetic capacity is required for Earth System models to simulate carbon assimilation reliably. Here we use a global leaf-trait dataset to test whether photosynthetic capaci...

Background and aimsRoot-released carboxylates enhance the availability of manganese (Mn), which enters roots through transporters with low substrate specificity. Leaf Mn concentration ([Mn]) has been proposed as a signature for phosphorus (P)-mobilising carboxylates in the rhizosphere. Here we test whether leaf [Mn] provides a signature for root fu...

Leaf-level gas exchange data support the mechanistic understanding of plant fluxes of carbon and water. These fluxes inform our understanding of ecosystem function, are an important constraint on parameterization of terrestrial biosphere models, are necessary to understand the response of plants to global environmental change, and are integral to e...

We introduce the AusTraits database - a compilation of measurements of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 375 traits across 29230 taxa from field campaigns, published literature, taxonomic monographs, and individual taxa descriptions. Traits vary in scope from physiological measures of...

Tropical forest ecosystems are undergoing rapid transformation as a result of changing environmental conditions and direct human impacts. However, we cannot adequately understand, monitor or simulate tropical ecosystem responses to environmental changes without capturing the high diversity of plant functional characteristics in the species-rich tro...

Tropical forest ecosystems are undergoing rapid transformation as a result of changing environmental conditions and direct human impacts. However, we cannot adequately understand, monitor or simulate tropical ecosystem responses to environ ⁎ mental changes without capturing the high diversity of plant functional characteristics in the species-rich...

Aims Anthropogenic climate change is predicted to increase mean temperatures and rainfall seasonality. How tropical rainforest species will respond to this climate change remains uncertain. Here we analyzed the effects of a 4-year experimental throughfall exclusion on an Australian endemic palm (Normambya normanbyi) in the Daintree rainforest of No...

Premise: Within closed-canopy forests, vertical gradients of light and atmospheric CO2 drive variations in leaf carbon isotope ratios, leaf mass per area (LMA), and the micromorphology of leaf epidermal cells. Variations in traits observed in preserved or fossilized leaves could enable inferences of past forest canopy closure and leaf function and...

The oxygen isotope composition (δ18O) of atmospheric carbon dioxide (CO2) can be used to estimate gross primary production at the ecosystem-scale and above. Understanding how and why the rate of oxygen isotope exchange between soil water and CO2 (kiso) varies can help to reduce uncertainty in the retrieval of such estimates. The expression and acti...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Background and aims: The stable carbon isotope ratio of leaf dry matter (γ13Cp) is generally a reliable recorder of intrinsic water-use efficiency in C3 plants. Here, we investigated a previously reported pattern of developmental change in leaf δ13Cp during leaf expansion, whereby emerging leaves are initially 13C-enriched compared to mature leave...

South‐East Australia has recently been subjected to two of the worst droughts in the historical record (Millennium Drought, 2000–2009 and Big Dry, 2017–2019). Unfortunately, a lack of forest monitoring has made it difficult to determine whether widespread tree mortality has resulted from these droughts. Anecdotal observations suggest the Big Dry ma...

Drought and heat stress significantly affect crop growth and productivity worldwide. It is unknown how heat interference during drought affects physiological processes dynamically in crops. Here we focussed on gas exchange and photochemistry in wheat and sorghum in response to simulated heat interference via +15°C of temperature during ~2 week drou...

Rising atmospheric CO2 concentrations and global warming can alter how plants partition their resources. This is important for food crops through changes in resource allocation to edible tissues and toxic defence compounds. While research suggests elevated temperature and [CO2] independently drive changes in plant metabolism and stress levels, and...

Recent decades have been characterized by increasing temperatures worldwide, resulting in an exponential climb in vapor pressure deficit (VPD). VPD has been identified as an increasingly important driver of plant functioning in terrestrial biomes and has been established as a major contributor in recent drought‐induced plant mortality independent o...

Conifers are, for the most part, competitively excluded from tropical rainforests by angiosperms. Where they do occur, conifers often occupy sites that are relatively infertile. To gain insight into the physiological mechanisms by which angiosperms outcompete conifers in more productive sites, we grew seedlings of a tropical conifer (Podocarpus gua...

Climate change scenarios predict increasing atmospheric CO 2 concentrations ([CO 2 ]), temperatures and droughts in tropical regions. Individually, the effects of these climate factors on plants are well established, whereas experiments on the interactive effects of a combination of factors are rare. Moreover, how these environmental factors will a...

Climate change is a worldwide threat to biodiversity and ecosystem structure, functioning, and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate‐change impacts across the soil–plant–atmosphere continuum...

In Australia, and other parts of the world, tower infrastructure in electricity transmission networks are nearing the end of their asset life. In changing economic, political and regulatory environments Transmission Network Service Providers are implementing new approaches to asset management and reinvestment, such as refurbishment to extend the li...

Stomata control the gas exchange of terrestrial plant leaves, and are therefore essential to plant growth and survival. We investigated gas exchange responses to vapor pressure deficit (VPD) in two grey poplar (Populus × canescens) lines: wild type (WT), and abscisic acid-insensitive (abi1) with functionally impaired stomata. Transpiration rate in...

Theoretical models of photosynthetic isotopic discrimination of CO2 (13C and 18O) are commonly used to estimate mesophyll conductance (gm). This requires making simplifying assumptions and assigning parameter values so that gm can be solved for as the residual term. Uncertainties in gm estimation occur due to measurement noise and assumptions not h...

Elevated CO2 (eCO2) experiments provide critical information to quantify the effects of rising CO2 on vegetation1–6. Many eCO2 experiments suggest that nutrient limitations modulate the local magnitude of the eCO2 effect on plant biomass1,3,5, but the global extent of these limitations has not been empirically quantified, complicating projections o...

High‐frequency stable isotope data are useful for validating atmospheric moisture circulation models and provide improved understanding of the mechanisms controlling isotopic compositions in tropical rainfall. Here we present a near‐continuous 6‐month record of O‐ and H‐isotope compositions in both water vapour and daily rainfall from Northeast Aus...

Plants actively regulate excess absorbed energy to protect photosynthetic machinery through heat dissipation in a process known as non-photochemical quenching (NPQ), a process useful for quantifying plant health and productivity. NPQ can be indirectly measured in the visible wavelengths between 500 nm and 560 nm, most commonly through the Photochem...