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Background and aims: Hakea prostrata (Proteaceae) is a highly phosphorus-use-efficient plant native to southwest Australia. It maintains a high photosynthetic rate at low leaf phosphorus (P) and exhibits delayed leaf greening, a convergent adaptation that increases nutrient-use efficiency. This study aimed to provide broad physiological and gene expression profiles across leaf development, uncovering pathways leading from young leaves as nutrient sinks to mature leaves as low-nutrient, energy-transducing sources. Methods: To explore gene expression underlying delayed greening, we analysed a de novo transcriptome for H. prostrata across five stages of leaf development. Photosynthesis and respiration rates, and foliar pigment, P and nitrogen (N) concentrations were determined, including the division of P into five biochemical fractions. Key results: Transcripts encoding functions associated with leaf structure generally decreased in abundance across leaf development, concomitant with decreases in foliar concentrations of 85% for anthocyanins, 90% for P and 70% for N. The expression of genes associated with photosynthetic function increased during or after leaf expansion, in parallel with increases in photosynthetic pigments and activity, much later in leaf development than in species that do not have delayed greening. As leaves developed, transcript abundance for cytosolic and mitochondrial ribosomal proteins generally declined, whilst transcripts for chloroplast ribosomal proteins increased. Conclusions: There was a much longer temporal separation of leaf cell growth from chloroplast development in H. prostrata than is found in species that lack delayed greening. Transcriptome-guided analysis of leaf development in H. prostrata provided insight into delayed greening as a nutrient-saving strategy in severely phosphorus-impoverished landscapes. [ABSTRACT FROM AUTHOR]

Climate change will impact gross primary productivity (GPP), net primary productivity (NPP), and carbon storage in wooded ecosystems. The extent of change will be influenced by thermal acclimation of photosynthesis—the ability of plants to adjust net photosynthetic rates in response to growth temperatures—yet regional differences in acclimation effects among wooded ecosystems is currently unknown. We examined the effects of changing climate on 17 Australian wooded ecosystems with and without the effects of thermal acclimation of C3 photosynthesis. Ecosystems were drawn from five ecoregions (tropical savanna, tropical forest, Mediterranean woodlands, temperate woodlands, and temperate forests) that span Australia's climatic range. We used the CABLE‐POP land surface model adapted with thermal acclimation functions and forced with HadGEM2‐ES climate projections from RCP8.5. For each site and ecoregion we examined (a) effects of climate change on GPP, NPP, and live tree carbon storage; and (b) impacts of thermal acclimation of photosynthesis on simulated changes. Between the end of the historical (1976–2005) and projected (2070–2099) periods simulated annual carbon uptake increased in the majority of ecosystems by 26.1%–63.3% for GPP and 15%–61.5% for NPP. Thermal acclimation of photosynthesis further increased GPP and NPP in tropical savannas by 27.2% and 22.4% and by 11% and 10.1% in tropical forests with positive effects concentrated in the wet season (tropical savannas) and the warmer months (tropical forests). We predicted minimal effects of thermal acclimation of photosynthesis on GPP, NPP, and carbon storage in Mediterranean woodlands, temperate woodlands, and temperate forests. Overall, positive effects were strongly enhanced by increasing CO2 concentrations under RCP8.5. We conclude that the direct effects of climate change will enhance carbon uptake and storage in Australian wooded ecosystems (likely due to CO2 enrichment) and that benefits of thermal acclimation of photosynthesis will be restricted to tropical ecoregions. [ABSTRACT FROM AUTHOR]

High air temperatures increase atmospheric vapor pressure deficit (VPD) and the severity of drought, threatening forests worldwide. Plants regulate stomata to maximize carbon gain and minimize water loss, resulting in a close coupling between net photosynthesis (Anet) and stomatal conductance (gs). However, evidence for decoupling of gs from Anet under extreme heat has been found. Such a response both enhances survival of leaves during heat events but also quickly depletes available water. To understand the prevalence and significance of this decoupling, we measured leaf gas exchange in 26 tree and shrub species growing in the glasshouse or at an urban site in Sydney, Australia on hot days (maximum Tair > 40°C). We hypothesized that on hot days plants with ample water access would exhibit reduced Anet and use transpirational cooling leading to stomatal decoupling, whereas plants with limited water access would rely on other mechanisms to avoid lethal temperatures. Instead, evidence for stomatal decoupling was found regardless of plant water access. Transpiration of well‐watered plants was 23% higher than model predictions during heatwaves, which effectively cooled leaves below air temperature. For hotter, droughted plants, the increase in transpiration during heatwaves was even more pronounced—gs was 77% higher than model predictions. Stomatal decoupling was found for most broadleaf evergreen and broadleaf deciduous species at the urban site, including some wilted trees with limited water access. Decoupling may simply be a passive consequence of the physical effects of high temperature on plant leaves through increased cuticular conductance of water vapor, or stomatal decoupling may be an adaptive response that is actively regulated by stomatal opening under high temperatures. This temperature response is not yet included in any land surface model, suggesting that model predictions of evapotranspiration may be underpredicted at high temperature and high VPD. [ABSTRACT FROM AUTHOR]

Background and Aims: Phosphorus (P) is a restricting nutrient for crop productivity worldwide. P deficiency can lead to stunted growth and development, eventually affecting crop yield. But less is documented about the impact of P fertility on industrial hemp (Cannabis sativa L.) production in the low-P soils of south-western Australia. We aimed to investigate the effect of P rates on growth, physiology, rhizosphere carboxylate exudation, nutrient uptake and P-use efficiency in hemp. Methods: The study was conducted in a randomised complete block design with four P rates (0, 40, 80 and 120 mg P kg–1 dry soil) and three hemp varieties (Morpeth, Han FNQ and Fedora 17). Plants were grown and raised in a controlled-environment phytotron until harvested 35 days after sowing at vegetative growth stage (3rd to nth leaf pair). Results: Our results revealed a strong influence of treatment (P rate) on hemp growth, physiology, biomass, nutrient uptake and P-use efficiency compared to variety and the variety × treatment interaction. Hemp roots predominantly released citrate in P-deficient conditions and gradually shifted to malate exudation with increasing P supply. The N:P ratio, leaf chlorophyll, and gas exchange data coupled with shoot and root length data suggest that Morpeth and Fedora 17 differ in morpho-physiological adaptations for optimum photosynthesis and growth, with high leaf chlorophyll and coarse root length achieved by Morpeth and high intercellular CO2 concentration and shoot length by Fedora 17. Conclusions: Morpeth and Fedora 17 had high shoot biomass, root length, root surface area and agronomic P-use and P-utilisation efficiencies in response to increasing soil P, while Han FNQ had moderate shoot yield, root growth, high citrate exudation, tissue P concentration and P-uptake efficiency. [ABSTRACT FROM AUTHOR]

Many forest ecosystems are in decline around the world due to increasing biotic and abiotic stresses. Marri (Corymbia calophylla) is an endemic and common eucalypt species of southwestern Australia, which is in decline primarily due to stem canker caused by the pathogenic fungus Quambalaria coyrecup. This study determined to what extent disease susceptibility and plant growth were associated with climate at origin for eight provenances of marri. Plants of all provenances were grown in a common garden with or without pathogen inoculation. Disease development and physiological performance of plants were monitored during an initial irrigated and subsequent terminal drought period. Provenances from drier regions were more susceptible to the fungal pathogen than those from wetter regions, having on average 31% higher incidence rates at 20 days post‐inoculation (dpi) and larger canker lesions at 130 dpi (on average 49% increase) and 230 dpi (on average 42% increase). However, canker development for each provenance was fastest during the initial irrigated wetter growing period. Overall, the average relative canker growth rate was 4‐fold higher during the irrigated period compared to the terminal drought period (p <.001). There were no significant differences between the provenances in leaf water status, photosynthetic rates, or relative growth rates (p >.05). Canker infection reduced both photosynthetic rates and growth rates but only during the later part of the terminal drought period, with significant (p <.05) reductions observed in two out of eight provenances, when plants had relatively large canker sizes. This effect tended to be strongest in the provenances from drier regions as they had relatively larger canker sizes than the provenances from wetter regions. We propose that the increased susceptibility of drier provenances is related to their lower exposure to the pathogen in their drier habitats. Since this is potentially due to suboptimal defence responses, using provenances from drier locations to 'future‐proof' local restoration outcomes in a drying climate may be counterproductive due to plant–pathogen interactions. [ABSTRACT FROM AUTHOR]

Cystophora is the second largest genus of fucoids worldwide and, like many other forest‐forming macroalgae, is increasingly threatened by a range of anthropogenic impacts including ocean warming. Yet, limited ecological information is available from the warm portion of their range (SW Western Australia), where severe range contractions are predicted to occur. Here, we provide the first insights on the abundance, diversity, productivity, and stand structure of Cystophora forests in this region. Forests were ubiquitous over more than 800 km of coastline and dominated sheltered and moderately‐exposed reefs. Stand biomass and productivity were similar or greater than that of kelp forests in the temperate reef communities examined, suggesting that Cystophora spp. play a similarly important ecological role. The stand structure of Cystophora forests was, however, different than those of kelp forests, with most stands featuring an abundant bank of sub‐canopy juveniles and only a few plants forming the canopy layer. Stand productivity followed an opposite seasonal pattern than that of kelps, with maximal growth in late autumn through early winter and net biomass loss in summer. Annually, stands contributed between 2.2 and 5.7 kg · m−2 (fresh biomass) to reef productivity depending on the dominant stand species. We propose that Cystophora forests play an important and unique role in supporting subtidal temperate diversity and productivity throughout temperate Australia, and urge a better understanding of their ecology and responses to anthropogenic threats. [ABSTRACT FROM AUTHOR]

SUMMARY: High temperature stress inhibits photosynthesis and threatens wheat production. One measure of photosynthetic heat tolerance is Tcrit – the critical temperature at which incipient damage to photosystem II (PSII) occurs. This trait could be improved in wheat by exploiting genetic variation and genotype‐by‐environment interactions (GEI). Flag leaf Tcrit of 54 wheat genotypes was evaluated in 12 thermal environments over 3 years in Australia, and analysed using linear mixed models to assess GEI effects. Nine of the 12 environments had significant genetic effects and highly variable broad‐sense heritability (H2 ranged from 0.15 to 0.75). Tcrit GEI was variable, with 55.6% of the genetic variance across environments accounted for by the factor analytic model. Mean daily growth temperature in the month preceding anthesis was the most influential environmental driver of Tcrit GEI, suggesting biochemical, physiological and structural adjustments to temperature requiring different durations to manifest. These changes help protect or repair PSII upon exposure to heat stress, and may improve carbon assimilation under high temperature. To support breeding efforts to improve wheat performance under high temperature, we identified genotypes superior to commercial cultivars commonly grown by farmers, and demonstrated potential for developing genotypes with greater photosynthetic heat tolerance. Significance Statement: Here we examined intraspecific variation in photosynthetic heat tolerance (the critical temperature at which damage to PSII occurs ‐ Tcrit); effects of genotype‐by‐environment interactions on Tcrit; and environmental drivers of Tcrit in wheat – the most widely cultivated crop. Our study provides a sound framework for identifying germplasm with superior Tcrit relative to well‐adapted commercial cultivars. This framework can be applied in agricultural and ecological settings in selection of more heat tolerant species. [ABSTRACT FROM AUTHOR]

Seaweed has garnered increasing interest due to its capacity to mitigate climate change by curbing carbon emissions from agriculture, as well as its potential to serve as a supplement or alternative for dietary, livestock feed, or fuel source production. Moreover, seaweed is regarded as one of the earliest plant forms to have evolved on Earth. Owing to the extensive body of literature available and the uncertainty surrounding the future trajectory of seaweed research under evolving climate conditions, this review scrutinizes the structure, dynamics, and progression of the literature pertaining to seaweed and climate change. This analysis is grounded in the Web of Science Core Collection database, augmented by CiteSpace software. Furthermore, we discuss the productivity and influence of individual researchers, research organizations, countries, and scientific journals. To date, there have been 8047 articles published globally (after a series of filters and exclusions), with a notable upswing in publication frequency since 2018. The USA, China, and Australia are among the leading countries contributing to this research area. Our findings reveal that current research on seaweed and climate change encompasses 13 distinct research clusters, including "marine heatwave", "temperate estuary", "ocean acidification", and "macroalgal bloom". The most frequently cited keywords are "climate change", "biomass", "community", and "photosynthesis". The seaweed species most commonly referenced in relation to climate change include Gracilaria sp., Sargassum sp., Ecklonia maxima , and Macrocystis pyrifera. These results provide valuable guidance for shaping the direction of specialized topics concerning marine biodiversity under shifting climate conditions. We propose that seaweed production may be compromised during prolonged episodes of reduced water availability, emphasizing the need to formulate strategies to guarantee its continued viability. This article offers fresh perspectives on the analysis of seaweed research in the context of impending climate change. • Linking a global trends of seaweed and climate change literature. • Five countries with 60% of publications, USA, Australia, China, France, Spain. • Collaboration networks actively occurred in the last five years. • Keywords analysis revealed "Growth", "macroalgae" and climate change" are previous focus study. • Four keywords - "blue carbon", "tolerance", "yield" and "marine heatwave" are recently receiving strongest attention. [ABSTRACT FROM AUTHOR]

Poorly-structured dense clay subsoils are widespread in dryland cropping regions in south-eastern Australia. They limit nutrient and water uptake from the subsoil which can limit grain yields. Recent research has shown that ameliorating subsoils with organic amendments can improve yields on these soils but the mechanisms underpinning this response remain unclear. Thus, different subsoil amelioration practices were imposed once at the high- and medium-rainfall sites followed with different crop sequences from 2018 to 2020. Both sites had poorly-structured sodic clay subsoils. The four experimental treatments assessed were 1) unamended control, 2) deep-banded gypsum, 3) chicken manure pellets applied to the topsoil, and (4) deep-banded in the subsoil. Compared to the control, both manure treatments significantly (p < 0.05) increased greenness in the upper leaves (SPAD readings), the green leaf area, and green leaf duration, and thereby delayed canopy senescence. The manures generally increased leaf N concentrations at anthesis, and at mid grain fill in all cereal crops, but not in faba bean. The manures also increased photosynthetic rates and instantaneous transpiration efficiencies (ITEs) in upper leaves of both cereal and faba bean crops, during grain or pod fill, but not in very dry years. Only one site and year combination, i.e. Tatyoon in 2018, showed an increase in grain yield. Despite the favourable effects of manures on crop canopies, unfavourable seasonal (rainfall) conditions were considered to be the major factor that limited yield increases by manured crops. Manuring in the medium-rainfall regions is likely ineffective in terms of crop productivity improvement. [Display omitted] • The manures generally increased greenness and leaf N concentrations in cereal crops. • The manures increased photosynthetic properties in crops but not in very dry years. • Unfavourable seasonal rainfall likely limited yield increases by manured crops. [ABSTRACT FROM AUTHOR]

One way to increase yield potential in wheat is screening for natural variation in photosynthesis. This study uses measured and modelled physiological parameters to explore genotypic diversity in photosynthetic capacity (P c, Rubisco carboxylation capacity per unit leaf area at 25 °C) and efficiency (P eff, P c per unit of leaf nitrogen) in wheat in relation to fertilizer, plant stage, and environment. Four experiments (Aus1, Aus2, Aus3, and Mex1) were carried out with diverse wheat collections to investigate genetic variation for Rubisco capacity (V cmax25), electron transport rate (J), CO2 assimilation rate, stomatal conductance, and complementary plant functional traits: leaf nitrogen, leaf dry mass per unit area, and SPAD. Genotypes for Aus1 and Aus2 were grown in the glasshouse with two fertilizer levels. Genotypes for Aus3 and Mex1 experiments were grown in the field in Australia and Mexico, respectively. Results showed that V cmax25 derived from gas exchange measurements is a robust parameter that does not depend on stomatal conductance and was positively correlated with Rubisco content measured in vitro. There was significant genotypic variation in most of the experiments for P c and P eff. Heritability of P c reached 0.7 and 0.9 for SPAD. Genotypic variation and heritability of traits show that there is scope for these traits to be used in pre-breeding programmes to improve photosynthesis with the ultimate objective of raising yield potential. [ABSTRACT FROM AUTHOR]

As the ratio of carbon uptake to water use by vegetation, water‐use efficiency (WUE) is a key ecosystem property linking global carbon and water cycles. It can be estimated in several ways, but it is currently unclear how different measures of WUE relate, and how well they each capture variation in WUE with soil moisture availability. We evaluated WUE in an Acacia‐dominated woodland ecosystem of central Australia at various spatial and temporal scales using stable carbon isotope analysis, leaf gas exchange and eddy covariance (EC) fluxes. Semi‐arid Australia has a highly variable rainfall pattern, making it an ideal system to study how WUE varies with water availability. We normalized our measures of WUE across a range of vapour pressure deficits using g1, which is a parameter derived from an optimal stomatal conductance model and which is inversely related to WUE. Continuous measures of whole‐ecosystem g1 obtained from EC data were elevated in the 3 days following rain, indicating a strong effect of soil evaporation. Once these values were removed, a close relationship of g1 with soil moisture content was observed. Leaf‐scale values of g1 derived from gas exchange were in close agreement with ecosystem‐scale values. In contrast, values of g1 obtained from stable isotopes did not vary with soil moisture availability, potentially indicating remobilization of stored carbon during dry periods. Our comprehensive comparison of alternative measures of WUE shows the importance of stomatal control of fluxes in this highly variable rainfall climate and demonstrates the ability of these different measures to quantify this effect. Our study provides the empirical evidence required to better predict the dynamic carbon–water relations in semi‐arid Australian ecosystems. [ABSTRACT FROM AUTHOR]

Platycerium bifurcatum is an epiphytic fern, occurring mainly in the forests of Australia and New Guinea. The location and spatial structure of its sporangia makes this fern a unique research model for physiological experiments. Our research aimed to determine changes in photosynthesis in the sporophilic and trophophilic parts of P. bifurcatum leaves during spore tying and maturation. For this purpose, the JIP-test and gas-exchange measurements of leaves were performed. In the study, we showed that changes typical of plant responses to stress factors also happened at critical periods in plant ontogenesis (e.g., in the generative phase) not related to environmental stress. Measurements of chlorophyll a fluorescence kinetics, the intensities of net/gross photosynthetic rate, and the respiration of sporotrophophilic leaves indicated that the intensities of these processes were related to the location of spores and to the stage of sporulation. The results are the first to describe the photosynthesis process and dark respiration of leaves during sporulation in ferns. [ABSTRACT FROM AUTHOR]

In this review, I first address the basics of gas exchange, water‐use efficiency and carbon isotope discrimination in C3 plant canopies. I then present a case study of water‐use efficiency in northern Australian tree species. In general, C3 plants face a trade‐off whereby increasing stomatal conductance for a given set of conditions will result in a higher CO2 assimilation rate, but a lower photosynthetic water‐use efficiency. A common garden experiment suggested that tree species which are able to establish and grow in drier parts of northern Australia have a capacity to use water rapidly when it is available through high stomatal conductance, but that they do so at the expense of low water‐use efficiency. This may explain why community‐level carbon isotope discrimination does not decrease as steeply with decreasing rainfall on the North Australian Tropical Transect as has been observed on some other precipitation gradients. Next, I discuss changes in water‐use efficiency that take place during leaf expansion in C3 plant leaves. Leaf phenology has recently been recognised as a significant driver of canopy gas exchange in evergreen forest canopies, and leaf expansion involves changes in both photosynthetic capacity and water‐use efficiency. Following this, I discuss the role of woody tissue respiration in canopy gas exchange and how photosynthetic refixation of respired CO2 can increase whole‐plant water‐use efficiency. Finally, I discuss the role of water‐use efficiency in driving terrestrial plant responses to global change, especially the rising concentration of atmospheric CO2. In coming decades, increases in plant water‐use efficiency caused by rising CO2 are likely to partially mitigate impacts on plants of drought stress caused by global warming. [ABSTRACT FROM AUTHOR]

Members of the Orchidaceae, one of the largest families of flowering plants, evolved the crassulacean acid metabolism (CAM) photosynthesis strategy. It is thought that CAM triggers adaptive radiation into new niche spaces, yet very little is known about its origin and diversification on different continents. Here, we assess the prevalence of CAM in Dendrobium , which is one of the largest genera of flowering plants and found in a wide range of environments, from the high altitudes of the Himalayas to relatively arid habitats in Australia. Based on phylogenetic time trees, we estimated that CAM, as determined by δ 13C values less negative than –20.0‰, evolved independently at least eight times in Dendrobium. The oldest lineage appeared in the Asian clade during the middle Miocene, indicating the origin of CAM was associated with a pronounced climatic cooling that followed a period of aridity. Divergence of the four CAM lineages in the Asian clade appeared to be earlier than divergence of those in the Australasian clade. However, CAM species in the Asian clade are much less diverse (25.6%) than those in the Australasian clade (57.9%). These findings shed new light on CAM evolutionary history and the aridity levels of the paleoclimate on different continents. [ABSTRACT FROM AUTHOR]

Tradescantia fluminensis is an invasive plant species in New Zealand, Australia and parts of the USA. It reproduces vegetatively and can grow to form dense mats up to 60 cm deep. Growth is limited by available light, and shading is one of the few effective methods of control. In this paper, we develop a dynamic model of a vertical cross section of a T. fluminensis mat, capturing vertical variation in its biomass and internal light intensity. We measure both variables at different heights in experimental mats of the species and use these data to parameterize the model. The model produces realistic vertical biomass and light intensity profiles. We show that the mat grows to a steady-state biomass that depends only on: (i) the light absorption coefficient, which we estimate from experimental data and (ii) the ratio of photosynthesis to respiration rate. This steady state undergoes a transcritical bifurcation; when the ambient light intensity falls below a critical level, the biomass shrinks to zero and the mat cannot survive. [ABSTRACT FROM AUTHOR]

Photosynthesis is a key biological process. However, we know little about whether plants change their photosynthetic strategy when introduced to a new range. We located the most likely source population for the South African beach daisy Arctotheca populifolia introduced to Australia in the 1930s, and ran a common-garden experiment measuring 10 physiological and morphological leaf traits associated with photosynthesis. Based on predictions from theory, and higher rainfall in the introduced range, we hypothesized that introduced plants would have a (i) higher photosynthetic rate, (ii) lower water-use efficiency (WUE) and (iii) higher nitrogen-use efficiency. However, we found that introduced A. populifolia had a lower photosynthetic rate, higher WUE and lower nitrogen-use efficiency than did plants from Arniston, South Africa. Subsequent site visits suggested that plants in Arniston may be able to access moisture on a rocky shelf, while introduced plants grow on sandy beaches where water can quickly dissipate. Our unexpected findings highlight that: (1) it is important to compare introduced species to their source population for an accurate assessment of evolutionary change; (2) rainfall is not always a suitable proxy for water availability and (3) introduced species often undergo evolutionary changes, but without detailed ecological information we may not be able to accurately predict the direction of these changes. [ABSTRACT FROM AUTHOR]

Photosynthesis in the seagrass Zostera muelleri remains poorly understood. We investigated the effect of reduced irradiance on the incorporation of 13C, gene expression of photosynthetic, photorespiratory and intermediates recycling genes as well as the enzymatic content and activity of Rubisco and PEPC within Z. muelleri. Following 48 h of reduced irradiance, we found that i) there was a ∼7 fold reduction in 13C incorporation in above ground tissue, ii) a significant down regulation of photosynthetic, photorespiratory and intermediates recycling genes and iii) no significant difference in enzyme activity and content. We propose that Z. muelleri is able to alter its physiology in order to reduce the amount of C lost through photorespiration to compensate for the reduced carbon assimilation as a result of reduced irradiance. In addition, the first estimated rate constant (K cat) and maximum rates of carboxylation (V cmax) of Rubisco is reported for the first time for Z. muelleri. • Photosynthetic carbon fixation is reduced in Zostera muelleri when exposed to low irradiance. • Photosynthesis, photorespiration and intermediates recycling genes are down regulated. • No significant changes in Rubisco content or phosphoenol pyruvate carboxylase activity. [ABSTRACT FROM AUTHOR]

The Jurien Bay dune chronosequence in south‐western Australia's biodiversity hotspot comprises sites differing in nutrient availability, with phosphorus (P) availability declining strongly with increasing soil age. We have explored the exceptionally high photosynthetic P‐use efficiency (PPUE) of Proteaceae in this region, triggering the question what the PPUE of co‐occurring species in other families might be along the Jurien Bay chronosequence.We explored how traits associated with PPUE, photosynthetic nitrogen (N)‐use efficiency (PNUE) and leaf respiration might converge along the chronosequence, and whether Proteaceae and non‐Proteaceae species differ in leaf traits associated with nutrient use.Seven to 10 species were sampled at three sites differing in nutrient availability (ranging from N‐ to P‐limited). Measurements of leaf light‐saturated photosynthesis and dark respiration were integrated with measurements of total N and P concentration in both mature and senesced leaves, and leaf mass per unit area (LMA).Contrary to what is known for other chronosequences, rates of photosynthesis and respiration did not decrease with increasing soil age and LMA along the Jurien Bay chronosequence. However, they increased when expressed per unit leaf P. Both N and P were used much more efficiently for photosynthesis on nutrient‐poor sites, in both Proteaceae and non‐Proteaceae species. Proteaceae had the fastest rate of photosynthesis per unit leaf P, followed by species that preferentially allocate P to mesophyll cells, rather than epidermal cells.Synthesis. Our results show that with declining soil P availability, photosynthetic P‐use efficiency of all investigated species from different families increased. Plants growing on the oldest, most nutrient‐impoverished soils exhibited similar rates of CO2 exchange as plants growing on more nutrient‐rich younger soils, and extraordinarily high photosynthetic P‐use efficiency. This indicates convergence in leaf traits related to photosynthetic nutrient use on severely P‐impoverished sites. [ABSTRACT FROM AUTHOR]

Mycoheterotrophs, i.e. plants that acquire carbon from root-associated soil fungi, often have highly degraded plastomes, reflecting relaxed selective constraints on plastid genes following the loss of photosynthesis. Geosiris Baill. is the only mycoheterotrophic genus in Iridaceae and comprises two species in Madagascar and nearby islands, and a third recently discovered species in north-eastern Australia. Here, we characterise the plastomes of the Australian and one Madagascan species to compare patterns of plastome degradation in relation to autotrophic and other mycoheterotrophic taxa and investigate the evolutionary and biogeographical history of the genus in Iridaceae. Both examined species have lost approximately half their plastid-encoded genes and a small but significant reduction in purifying selection in retained non-photosynthetic genes was observed. Geosiris is confirmed as monophyletic, with initial divergence of the genus occurring c. 53 million years ago, and subsequent diversification occurring c. 30 million years ago. Africa (including Madagascar) is reconstructed as the most likely ancestral area of the genus, implying a major range-expansion event of one lineage to Australia after its divergence in the Oligocene. Our study has highlighted the dynamic evolutionary history of Geosiris , contributed to the characterisation of mycoheterotrophic plastomes, and furthered our understanding of plastome structure and function. [ABSTRACT FROM AUTHOR]

The Sydney Harbour Estuary is a large drowned river valley adjacent to Sydney, a large urban metropolis on track to become a megacity; estimated to reach a population of 10 million by 2100. Monthly underway surveys of surface water p CO 2 were undertaken along the main channel and tributaries, from January to December 2013. p CO 2 showed substantial spatio-temporal variability in the narrow high residence time upper and mid sections of the estuary, with values reaching a maximum of 5650 μatm in the upper reaches and as low as 173 μatm in the mid estuary section, dominated by respiration and photosynthesis respectively. The large lower estuary displayed less variability in pCO 2 with values ranging from 343 to 544 μatm controlled mainly by tidal pumping and temperature. Air-water CO 2 emissions reached a maximum of 181 mmol C m −2 d −1 during spring in the eutrophic upper estuary. After a summer high rainfall event nutrient-stimulated biological pumping promoted a large uptake of CO 2 transitioning the Sydney Harbour Estuary into a CO 2 sink with a maximum uptake of rate of −10.6 mmol C m −2 d −1 in the mid-section of the estuary. Annually the Sydney Harbour Estuary was heterotrophic and a weak source of CO 2 with an air-water emission rate of 1.2–5 mmol C m −2 d −1 (0.4–1.8 mol C m −2 y −1 ) resulting in a total carbon emission of around 930 tonnes per annum. CO 2 emissions (weighted m 3 s −1 of discharge per km 2 of estuary surface area) from Sydney Harbour were an order of magnitude lower than other temperate large tectonic deltas, lagoons and engineered systems of China, India, Taiwan and Europe but were similar to other natural drowned river valley systems in the USA. Discharge per unit area appears to be a good predictor of CO 2 emissions from estuaries of a similar climate and geomorphic class. [ABSTRACT FROM AUTHOR]

In the flora of Australia, the driest vegetated continent, crassulacean acid metabolism (CAM), the most water-use efficient form of photosynthesis, is documented in only 0.6% of native species. Most are epiphytes and only seven terrestrial. However, much of Australia is unsurveyed, and carbon isotope signature, commonly used to assess photosynthetic pathway diversity, does not distinguish between plants with low-levels of CAM and C3 plants. We provide the first census of CAM for the Australian flora and suggest that the real frequency of CAM in the flora is double that currently known, with the number of terrestrial CAM species probably 10-fold greater. Still unresolved is the question why the large stem-succulent life — form is absent from the native Australian flora even though exotic large cacti have successfully invaded and established in Australia. [ABSTRACT FROM AUTHOR]

Warming trends involve two agronomically relevant aspects: a gradual increase in long-term mean temperature with the primary effect of shifting phenological patterns, and an increasing incidence of heat waves. Depending on timing, intensity and duration, heat can reduce crop growth and disrupt reproduction. Agronomic and breeding adaptations to elevated temperature have been listed but there is an overall lack of frameworks for systematic analysis. This paper provides agronomic and physiological background for the quantitative assessment of spatial patterns of the thermal regimes for wheat, barley, canola, field pea and chickpea. First, we revise the notion that Australian agriculture is 'European' and ill-adapted to the local environments. By showing that Australian agriculture in the southern and western regions is rather Levantine, we advance a more accurate and relevant framework to the thermal regimes of winter crops. Second, we outline the direct and indirect effects of temperature on crop traits and highlight the limitations of different approaches to investigate crop responses to temperature. This is important to make explicit the assumptions of studies dealing with crop responses to temperature; for example, indirect effects of temperature on crops mediated by effects on weeds, pathogens or herbivores could be important. Third, we compare the cardinal temperatures (including base, optimal, and critical thresholds) of our target crops. Cardinal temperatures respond to both natural and agronomic selection and are relevant for crop adaptation. Fourth, we develop a conceptual framework to assess thermal effects on crop yield and adaptive practices and traits, based on the notions of yield being a primary function of seed number, the species-specific critical window for the determination of seed number, and two complementary perspectives involving the photothermal quotient and crop growth rate in the critical window. The framework accounts for both aspects of warming: non-stressful elevated temperature and heat stress. Testable propositions are advanced that inform future research on crop adaptation to elevated temperature. [ABSTRACT FROM AUTHOR]

• Four key environmental variables are identified that significantly influence the CO 2 flux. • Light- and water-use efficiencies in overcast skies are double those in sunny skies. • The diffuse effect correlates with the observed in-crop shortwave radiation penetration. The relationships between the daytime CO 2 flux density above a wheat crop and both solar irradiance and evapotranspiration are investigated using physical and biophysical measurements made in 1971 in Australia. Well-established flux‒gradient relations are used to estimate the hourly CO 2 flux density using the measured CO 2 concentration at heights of 1 m and 2 m above the crop. Principal component regression identifies four key environmental variables (diffuse and beam shortwave irradiance, leaf-area index, humidity deficit) whose variations together explain almost 80% of the variations in the hourly CO 2 flux. For the diffuse ratio S d / S g ≈ 0.9 (generally overcast skies), where S d and S g are the observed diffuse and global broadband shortwave irradiances (wavelength range 285 nm to 2800 nm), respectively, both light-use and water-use efficiencies are found to be around double those for S d / S g ≈ 0.1 (sunny skies). For a given value of S g this doubling in the water-use efficiency is primarily due to the sensitivity of the CO 2 flux to the diffuse ratio. Profile measurements of narrowband (350 to 950 nm) irradiance within the canopy confirm that the increase in light-use efficiency is primarily due to the greater interception of radiation in the canopy under an increased diffuse ratio, up to 15 percent in overcast conditions. [ABSTRACT FROM AUTHOR]

Vegetation growth drives many of the interactions between the land surface and atmosphere including the uptake of carbon through photosynthesis and loss of water through transpiration. In arid and semi-arid regions water is the dominant driver of vegetation growth. However, few studies consider the fact that water can move laterally across the landscape as runoff via streams and floodplains, termed hydrologic connectivity. Using multiple observations alongside models and a hydromorphology dataset for Australia, we examine how ecosystems with high hydrologic connectivity differ in their vegetation response to water availability, soil properties, and interannual variability and extremes in vegetation productivity. We find that the average interannual variability of vegetation productivity is 21–34% higher in ecosystems with high hydrologic connectivity, with skewed annual anomalies showing larger extremes in carbon uptake. This is driven by a higher average and more variable surface soil moisture and significantly higher soil available water capacity and soil depth. These spatially small ecosystems, covering 14% of the study region, contribute 15–22% (median = 17%) to regional-scale carbon uptake through higher rates of gross photosynthesis, especially evident during wet years, and 3–37% (median = 19%) to annual anomalies. Current global land surface models do not reproduce the observed spatial patterns of interannual variability in carbon uptake over regions where hydrologic connectivity is high as they lack the mechanism of connectivity of water between discrete land surface elements. This study highlights the significant role of riparian and floodplain vegetation on the interannual variability and extremes of the regional carbon cycle. • Multiple satellite and ancillary datasets are used to study carbon-water interactions in Australia. • High variability and extremes in plant growth occur in riparian and floodplain ecosystems. • Hydrologically connected ecosystems are important contributors to regional GPP. • TRENDY models misrepresent GPP in areas with high hydrologic connectivity. [ABSTRACT FROM AUTHOR]

Recent findings have shown that photosynthesis in the skin of the seed of Posidonia oceanica enhances seedling growth. The seagrass genus Posidonia is found only in two distant parts of the world, the Mediterranean Sea and southern Australia. This fact led us to question whether the acquisition of this novel mechanism in the evolution of this seagrass was a pre-adaptation prior to geological isolation of the Mediterranean from Tethys Sea in the Eocene. Photosynthetic activity in seeds of Australian species of Posidonia is still unknown. This study shows oxygen production and respiration rates, and maximum PSII photochemical efficiency (Fv : Fm) in seeds of two Australian Posidonia species (P. australis and P. sinuosa), and compares these with previous results for P. oceanica. Results showed relatively high oxygen production and respiratory rates in all three species but with significant differences among them, suggesting the existence of an adaptive mechanism to compensate for the relatively high oxygen demands of the seeds. In all cases maximal photochemical efficiency of photosystem II rates reached similar values. The existence of photosynthetic activity in the seeds of all three species implicates that it was an ability probably acquired from a common ancestor during the Late Eocene, when this adaptive strategy could have helped Posidonia species to survive in nutrient-poor temperate seas. This study sheds new light on some aspects of the evolution of marine plants and represents an important contribution to global knowledge of the paleogeographic patterns of seagrass distribution. [ABSTRACT FROM AUTHOR]

Leaf photosynthetic CO2 responses can provide insight into how major nutrients, such as phosphorus ( P), constrain leaf CO2 assimilation rates ( Anet). However, triose-phosphate limitations are rarely employed in the classic photosynthesis model and it is uncertain as to what extent these limitations occur in field situations. In contrast to predictions from biochemical theory of photosynthesis, we found consistent evidence in the field of lower Anet in high [ CO2] and low [ O2] than at ambient [ O2]. For 10 species of trees and shrubs across a range of soil P availability in Australia, none of them showed a positive response of Anet at saturating [ CO2] (i.e. Amax) to 2 kPa O2. Three species showed >20% reductions in Amax in low [ O2], a phenomenon potentially explained by orthophosphate ( Pi) savings during photorespiration. These species, with largest photosynthetic capacity and Pi > 2 mmol P m−2, rely the most on additional Pi made available from photorespiration rather than species growing in P-impoverished soils. The results suggest that rarely used adjustments to a biochemical photosynthesis model are useful for predicting Amax and give insight into the biochemical limitations of photosynthesis rates at a range of leaf P concentrations. Phosphate limitations to photosynthetic capacity are likely more common in the field than previously considered. [ABSTRACT FROM AUTHOR]

The mission of this study is to compare Net Primary Productivity (NPP) estimates using (i) forest inventory data and (ii) spatio-temporally continuous MODIS (MODerate resolution Imaging Spectroradiometer) remote sensing data for Austria. While forest inventories assess the change in forest growth based on repeated individual tree measurements (DBH, height etc.), the MODIS NPP estimates are based on ecophysiological processes such as photosynthesis, respiration and carbon allocation. We obtained repeated national forest inventory data from Austria, calculated a "ground-based" NPP estimate and compared the results with "space-based" MODIS NPP estimates using different daily climate data. The MODIS NPP estimates using local Austrian climate data exhibited better compliance with the forest inventory driven NPP estimates than the MODIS NPP predictions using global climate data sets. Stand density plays a key role in addressing the differences between MODIS driven NPP estimates versus terrestrial driven inventory NPP estimates. After addressing stand density, both results are comparable across different scales. As forest management changes stand density, these findings suggest that management issues are important in understanding the observed discrepancies between MODIS and terrestrial NPP. [ABSTRACT FROM AUTHOR]

As rapid climate warming creates a mismatch between forest trees and their home environment, the ability of trees to cope with warming depends on their capacity to physiologically adjust to higher temperatures. In widespread species, individual trees in cooler home climates are hypothesized to more successfully acclimate to warming than their counterparts in warmer climates that may approach thermal limits. We tested this prediction with a climate-shift experiment in widely distributed Eucalyptus tereticornis and E. grandis using provenances originating along a ~2500 km latitudinal transect (15.5-38.0°S) in eastern Australia. We grew 21 provenances in conditions approximating summer temperatures at seed origin and warmed temperatures (+3.5 °C) using a series of climate-controlled glasshouse bays. The effects of +3.5 °C warming strongly depended on home climate. Cool-origin provenances responded to warming through an increase in photosynthetic capacity and total leaf area, leading to enhanced growth of 20-60%. Warm-origin provenances, however, responded to warming through a reduction in photosynthetic capacity and total leaf area, leading to reduced growth of approximately 10%. These results suggest that there is predictable intraspecific variation in the capacity of trees to respond to warming; cool-origin taxa are likely to benefit from warming, while warm-origin taxa may be negatively affected. [ABSTRACT FROM AUTHOR]

We present a conceptual model linking dry-mass allocational allometry, hydraulic limitation, and vertical stratification of environmental conditions to patterns in vertical tree growth and tree height. Maximum tree height should increase with relative moisture supply and both should drive variation in apparent stomatal limitation. Carbon isotope discrimination (∆) should not vary with maximum tree height across a moisture gradient when only hydraulic limitation or allocational allometry limit height, but increase with moisture when both hydraulic limitation and allocational allometry limit maximum tree height. We quantified tree height and ∆ along a gradient in annual precipitation from 300 to 1600 mm from mallee to temperate rain forest in southeastern Australia; Eucalyptus on this gradient span almost the entire range of tree heights found in angiosperms worldwide. Maximum tree height showed a strong, nearly proportional relationship to the ratio of precipitation to pan evaporation. ∆ increased with In P/Ep, suggesting that both hydraulic limitation and allocational allometry set maximum tree height. Coordinated shifts in several plant traits should result in different species having an advantage in vertical growth rate at different points along a rainfall gradient, and in maximum tree height increasing with relative moisture supply, photosynthetic rate, nutrient supply, and xylem diameter. [ABSTRACT FROM AUTHOR]

Large trees are critical components of forest ecosystems, but are declining in many forests worldwide. We predicted that growth of large trees is more vulnerable than that of small trees to high temperatures, because respiration and tissue maintenance costs increase with temperature more rapidly than does photosynthesis and these costs may be disproportionately greater in large trees. Using 5 00 000 measurements of eucalypt growth across temperate Australia, we found that high temperatures do appear to impose a larger growth penalty on large trees than on small ones. Average stem diameter growth rates at 21 °C compared with 11 °C mean annual temperature were 57% lower for large trees (58 cm stem diameter), but only 29% lower for small trees (18 cm diameter). While our results are consistent with an impaired carbon budget for large trees at warmer sites, we cannot discount causes such as hydraulic stress. We conclude that slower growth rates will impede recovery from extreme events, exacerbating the effects of higher temperatures, increased drought stress and more frequent fire on the tall eucalypt forests of southern Australia. [ABSTRACT FROM AUTHOR]

• Biocrust hydration led to a large and immediate increase in soil CO 2 flux. • Hydration initiates photosynthesis in some, but not all biocrusts. • Biocrusts are highly spatially variable at both landscape and small scales. Soil biocrusts, formed from communities of microbes and their extracellular products are a common feature of dryland soil surfaces. Biocrust organisms are only intermittently metabolically active, but due to their ubiquity they make a significant contribution to the carbon cycle. Quantification of the controls and insights into the interlinked process of photosynthesis and respiration are essential to enhancing our understanding of the carbon cycle in the world's drylands. Yet, there have been relatively few field studies investigating controls on both biocrust photosynthesis and respiration. We undertook field-based experiments at two dune sites during the dry season in Diamantina National Park in Queensland, Australia to determine how biocrust hydration and illumination affect soil CO 2 flux and photosynthesis. Static chambers and an infra-red gas analyser were used to quantify soil CO 2 flux, and a fluorometer and a CFImager were used to determine a range of photosynthetic parameters in the field and laboratory respectively. When dry, biocrust photosynthetic activity was not detected and soil CO 2 flux was very low irrespective of biocrust cover. Hydration led to a large and immediate increase in CO 2 flux, which was more pronounced in the presence of biocrusts and on the dune with thinner biocrusts. Hydration also initiated the onset of photosynthesis in some biocrusts, which was greatest under low light conditions and sustained with further hydration. There were only infrequent periods of net CO 2 uptake to the soil, occurring when CO 2 uptake due to photosynthetic activity was less than background soil CO 2 flux. Chlorophyll fluorescence imaging indicated biocrust spatial heterogeneity was evident at the cm scale where microtopography creates a myriad of environments for different crust organisms. Our findings demonstrate that biocrusts are highly spatially heterogenetic at both landscape and small scale, which suggests the maintenance of biocrust spatial diversity is likely to be key to imparting resilience to changing climate and disturbance. As well as reaffirming the importance of biocrusts for the carbon cycle in dryland dune soils the study demonstrates that biocrust respiration and photosynthesis respond differently to hydration and shading. This adds an unpredictability to the distribution of soil carbon stocks and the gaseous exchanges of CO 2 between the surface and atmosphere. Future changes to precipitation and increased temperatures are likely to reduce soil moisture across much of the Australian interior and consequently biocrusts may experience a decline in biomass, structure, and function which could have significant repercussions beyond carbon stocks. [ABSTRACT FROM AUTHOR]

Proteaceae species in south-western Australia occur on phosphorus- ( P) impoverished soils. Their leaves contain very low P levels, but have relatively high rates of photosynthesis. We measured ribosomal RNA ( rRNA) abundance, soluble protein, activities of several enzymes and glucose 6-phosphate ( Glc6P) levels in expanding and mature leaves of six Proteaceae species in their natural habitat. The results were compared with those for Arabidopsis thaliana. Compared with A. thaliana, immature leaves of Proteaceae species contained very low levels of rRNA, especially plastidic rRNA. Proteaceae species showed slow development of the photosynthetic apparatus ('delayed greening'), with young leaves having very low levels of chlorophyll and Calvin- Benson cycle enzymes. In mature leaves, soluble protein and Calvin- Benson cycle enzyme activities were low, but Glc6P levels were similar to those in A. thaliana. We propose that low ribosome abundance contributes to the high P efficiency of these Proteaceae species in three ways: (1) less P is invested in ribosomes; (2) the rate of growth and, hence, demand for P is low; and (3) the especially low plastidic ribosome abundance in young leaves delays formation of the photosynthetic machinery, spreading investment of P in rRNA. Although Calvin- Benson cycle enzyme activities are low, Glc6P levels are maintained, allowing their effective use. [ABSTRACT FROM AUTHOR]

Abstract: Satellite remote sensing products of the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) are routinely used for diverse applications in Earth-System and land-surface modelling and monitoring. The availability of numerous products creates a need to understand the level of consistency between products, and reasons for inconsistencies. We evaluate the consistency of six FAPAR products (MODIS, MERIS, SeaWIFS, MODIS-TIP, SPOT-VEG, and AVHRR) across the Australian continent, using multi-year records. We find that seemingly large differences in FAPAR products over much of Australia can be explained by a simple offset present in certain products. Additional inconsistencies arise from different sensitivities in FAPAR to changes in vegetation cover. These inconsistencies can in turn be partially attributed to changes in biome type that are relevant to certain products and related model-specific assumptions. The satellite FAPAR products are compared to ~800 observation-based estimates of fractional vegetation cover at field sites across Australia. After accounting for offsets in FAPAR, relatively high agreement occurs at sites classified as grasslands, shrublands and managed land (agriculture). Significant disagreement occurs at sites correctly classified as forests. Consequently, some products show significant differences in FAPAR between regions of similar vegetation cover but different biome classification. We find that all products show a much lower sensitivity to fractional vegetation cover (range in coefficient of linear regression: 0.28–0.61) than is predicted theoretically (0.96–1.18) using a canopy radiative transfer model. Reasons for this discrepancy are discussed. [Copyright &y& Elsevier]

Abstract: SeaWiFS surface chlorophyll estimates and Levitus nitrate estimates in the Southern Ocean south of Australia (140°E) show that this region is characterised by a high-nitrate low-chlorophyll (HNLC) regime typical of Southern Ocean waters. The HNLC conditions become more prominent moving south from the Sub-Antarctic Zone, with surface chlorophyll generally decreasing and nitrate increasing with latitude. Parameter optimisation experiments were performed using simulated annealing to fit a zero-dimensional nitrogen-based four-component ecosystem model to SeaWiFS surface chlorophyll data in the Sub-Antarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ). We hypothesise that bioavailability of iron limits phytoplankton growth in this region. A physiological indicator of iron availability was investigated by optimising three of the model parameters defining maximum photosynthetic growth and maximum photosynthetic efficiency of phytoplankton. The effect of zooplankton grazing and light, mixed layer depth and temperature forcing data on the optimisation results was investigated in further optimisation experiments. An error analysis of the optimised parameter estimates was performed by analysing the Hessian matrix of the cost function. The parameter optimisations indicate that phytoplankton growth rates in the Polar Frontal Zone and Antarctic Zone are limited by some process not explicitly included in this model, with iron availability being the most likely candidate. Based on these optimisations we support the theory that micronutrient availability is the primary cause of the HNLC conditions in the Australian sector of the Southern Ocean. [Copyright &y& Elsevier]

Oryza meridionalis is a wild species of rice, endemic to tropical Australia. It shares a significant genome homology with the common domesticated rice Oryza sativa. Exploiting the fact that the two species are highly related but O. meridionalis has superior heat tolerance, experiments were undertaken to identify the impact of temperature on key events in photosynthesis. At an ambient CO2 partial pressure of 38 Pa and irradiance of 1500 µmol quanta m−2 s−1, the temperature optimum of photosynthesis was 33.7 ± 0.8°C for O. meridionalis, significantly higher than the 30.6 ± 0.7°C temperature optimum of O. sativa. To understand the basis for this difference, we measured gas exchange and rubisco activation state between 20 and 42°C and modeled the response to determine the rate-limiting steps of photosynthesis. The temperature response of light respiration (Rlight) and the CO2 compensation point in the absence of respiration (Γ*) were determined and found to be similar for the two species. C3 photosynthesis modeling showed that despite the difference in susceptibility to high temperature, both species had a similar temperature-dependent limitation to photosynthesis. Both rice species were limited by ribulose-1,5-bisphosphate (RuBP) regeneration at temperatures of 25 and 30°C but became RuBP carboxylation limited at 35 and 40°C. The activation state of rubisco in O. meridionalis was more stable at higher temperatures, explaining its greater heat tolerance compared with O. sativa. [ABSTRACT FROM AUTHOR]

Abstract: We investigated crop and leaf photosynthetic traits in a set of Australian wheats released between 1958 and 2007. Environmental variation generated a range in pre-anthesis radiation use efficiency between 1.54 and 2.68gMJ−1. For these contrasting conditions, radiation use efficiency increased linearly with year of cultivar release at a rate of 0.012gMJ−1 per year. The fraction of incident radiation at different depths in the canopy profile increased linearly with year of cultivar release. Leaf greenness increased with year of cultivar release but the magnitude of this effect varied in the canopy profile; SPAD increased 0.24unitsyr−1 between 0 and 0.2m, 0.44unitsyr−1 between 0.2 and 0.3m, 0.22unitsyr−1 between 0.3 and flag leaf, and 0.11unitsyr−1 for the flag leaf. There was a sharp extinction of nitrogen concentration with canopy depth relative to the extinction of radiation in older varieties that shifted to a flatter nitrogen-radiation extinction in newer varieties. Increased radiation use efficiency in newer varieties was associated with the relaxation in the coupling between the extinction of nitrogen and radiation in the profile which was in turn partially related to the improved nitrogen status of modern varieties, as quantified with the nitrogen nutrition index. Stomata density (range: 38–56mm−2), stomata length (0.043–0.055μm), stomata width (0.024–0.032μm), light-saturated photosynthesis (9.3–19.6μmolm−2 s−1) and respiration (1.6–7.3μmolm−2 s−1) measured in the flag leaf at anthesis were unrelated to year of cultivar release. Shifts in crop-level traits associated with breeding and selection for yield were a likely source of improvement in pre-anthesis radiation use efficiency. [Copyright &y& Elsevier]

Abstract: With the ultimate aim of developing a Crop Design Tool that will specify resource-efficient ideotypes for any environment, modelling procedures are proposed and tested here whereby wheat phenology can be optimised according to risks of abiotic damage (frost, heat and drought) to seedling establishment and grain set. Then crop growth can be estimated from availability of water and solar radiation, and optimum DM partitioning to grain can be specified by allocating a minimum of support dry matter (DM) to stems (to resist lodging), leaves (to optimise photosynthesis), and flowers (to bear grains). Ideotypes for reference regions (with mature wheat breeding programmes) of the Mallee and Wimmera in Victoria, the Canturbury plains in New Zealand and Norfolk in the UK gave estimated grain yields of 1.9, 3.0, 7.2 and 6.2tha−1 DM respectively, similar to those shown by current cultivars, but with earlier flowering and harvest dates, with heavier stems, and high redistribution of stem DM to grain. Ideotypes for five sites in the Australian High Rainfall Zone showed high grain yield potentials, ranging from 4.5tha−1 DM at Kojonup to 7.8tha−1 DM at Hamilton, allowing for yield loss due to abiotic stress. These were characterised by early stem extension and flowering dates but also by long crop construction periods (from the start of stem extension to anthesis) of 800–1100°Cd and increased harvest indices compared to cultivars currently adopted from other regions. The challenges in testing these ideotypes will be in finding germplasm that demonstrates unusual phenology with short stature, and growing these to maximise light interception in spring. The main uncertainties in the estimation procedures arose from poor quality wind data, a poorly quantified association between stem material density and stem strength, and lack of data on maximum capacity to store redistributable stem DM. Sensitivity analysis showed grain yields of ideotypes to depend on maximum wind gusts during grain production as well as on plant-available water. The most effective single means of increasing potential grain yields was predicted clearly to be through increasing the conversion of radiation to DM. [Copyright &y& Elsevier]

Abstract: Savannas comprise a large proportion of the terrestrial land surface and are highly varied in their composition, structure and function. These characteristics alter land–atmosphere exchanges of heat, water, carbon dioxide and other trace gases, which feed back to the climate at multiple scales. Australian savannas provide significant ecosystem services and further systematic scientific study is needed to sustainably manage these ecosystems. We undertook an interdisciplinary research effort to understand the patterns and processes of carbon, water and energy cycles across northern Australian landscapes across scales from point to region. We quantified the land surface–atmosphere exchanges across the vast region of Australian savannas using a hierarchical, integrated measurement and modelling approach to determine regional greenhouse gas and water budgets. The research team comprised groups from seven institutions and four countries. The research effort comprised of a multi- year measurement and modelling endeavour and culminated in an intensive field program held in September 2008 (late dry season). The program aimed to improve our knowledge of the spatial and temporal variability of land–atmosphere exchanges and the processes driving them as well as our ability to remotely sense them and simulate them using land surface models, which are crucial components of Global Climate Models. We attempted to robustly integrate small scale processes, such as leaf photosynthesis to larger scales applicable to modelling and remote sensing for the savanna region. In this paper we provide the scientific background and our overall approach to the program with reference to the papers in this “Savanna Patterns of Energy and Carbon Integrated Across the Landscape” (SPECIAL) issue. [Copyright &y& Elsevier]

Savannas are highly significant global ecosystems that consist of a mix of trees and grasses and that are highly spatially varied in their physical structure, species composition, and physiological function (i.e., leaf area and function, stem density, albedo, and roughness). Variability in ecosystem characteristics alters biophysical and biogeochemical processes that can affect regional to global circulation patterns, which are not well characterized by land surface models. We initiated a multidisciplinary field campaign called Savanna Patterns of Energy and Carbon Integrated across the Landscape (SPECIAL) during the dry season in Australian savannas to understand the spatial patterns and processes of land surface-atmosphere exchanges (radiation, heat, moisture, CO2, and other trace gasses). We utilized a combination of multiscale measurements including fixed flux towers, aircraft-based flux transects, aircraft boundary layer budgets, and satellite remote sensing to quantify the spatial variability across a continental-scale rainfall gradient (transect). We found that the structure of vegetation changed along the transect in response to declining average rainfall. Tree basal area decreased from 9.6 m2 ha−1 in the coastal woodland savanna (annual rainfall 1,714 mm yr−1) to 0 m2 ha−1 at the grassland site (annual rainfall 535 mm yr−1), with dry-season green leaf area index (LAI) ranging from 1.04 to 0, respectively. Leaf-level measurements showed that photosynthetic properties were similar along the transect. Flux tower measurements showed that latent heat fluxes ( LEs) decreased from north to south with resultant changes in the Bowen ratios ( H/ LE) from a minimum of 1.7 to a maximum of 15.8, respectively. Gross primary productivity, net carbon dioxide exchange, and LE showed similar declines along the transect and were well correlated with canopy LAI, and fluxes were more closely coupled to structure than floristic change. [ABSTRACT FROM AUTHOR]

Abstract: The high nutrient low chlorophyll (HNLC) surface waters of the Southern Ocean are characterised by high concentrations of nitrate and phosphate, low concentrations of dissolved iron and deep vertical mixing. Future climate scenarios predict increased surface temperatures and ocean stratification in the region. These changes to vertical mixing will result in a slowdown of nutrient supply to surface waters and an increase in the integrated irradiance in the upper mixed layer. To investigate the influence of iron-limitation and high irradiance on phytoplankton growth and physiology, a 6-day shipboard incubation experiment was conducted during the Sub-Antarctic Zone Sensitivity to Environmental Change (SAZ Sense) voyage using phytoplankton populations from the upper mixed layer in the north-eastern SAZ region. Iron-limitation was induced with an organic siderophore and was compared with a 1nM iron-enriched incubation and an unamended treatment (under silicate replete conditions). As expected, iron enrichment led to dominance by large diatoms and enhanced photosynthetic performance, while the iron-limited community showed a decline in total chl a and photochemical efficiency. Under the added stress of high light, the iron-limited community was able to cope with the shift from in situ (<150μmolphotonsm−2 s−1) to incubation (mean=765μmolphotonsm−2 s−1) irradiance by increasing the proportion of photoprotective pigments and diverting excess light energy via energy-dependent quenching (q E). The responses to iron-limitation under high light showed that the phytoplankton community was able to acclimate to these conditions, but exhibited an overall decline in photosynthetic activity. Data presented here suggest the community shifts, in particular the decrease in diatoms, and the decline in photosynthetic performance of phytoplankton under low iron-high irradiance conditions has the potential to impact future ocean productivity and biogeochemical cycling. [Copyright &y& Elsevier]

Abstract: Marine primary production is a fundamental measure of the ocean''s capacity to convert carbon dioxide to particulate organic carbon for the marine foodweb, and as such is an essential variable used in ecosystem and biogeochemical models to assess trophic dynamics and carbon cycling. The Sub-Antarctic Zone (SAZ) is a major sink for atmospheric carbon and exhibits large gradients in ocean conditions on both temporal and spatial scales. In this dynamic system, an understanding of small-scale temporal changes is critical for modelling primary production at larger scales. Thus, we investigated diel effects on maximum quantum yield of PSII (F V/F M), photosynthetic pigment pools and primary productivity in the western (Diel 1) and eastern SAZ region (Diel 3) south of Tasmania, Australia, and compared this to a station at the polar front (Diel 2). Phytoplankton in the eastern SAZ had the greatest diel response, with cells showing decreased F V/F M and increased biosynthesis and transformation of xanthophyll and other photoprotective pigments during the day, but only in the surface waters (0 and 10m). Diel responses diminished by 30m. Cells in the western SAZ had similar responses across the depths sampled, increasing their F V/F M during the night and increasing their xanthophyll pigment content during the day. Phytoplankton at the polar front (Diel 2) showed intermediate diel-related variations in photophysiology, with xanthophyll conversion and increases in photoprotective pigments during the day but constant F V/F M. These diel changes at all sampling stations had little impact on carbon fixation rates, although cells sampled from the deep chlorophyll maximum at the polar front had significantly lower maximum carbon fixation and minimum saturating irradiance (E k ) compared to the other depths and stations. Considering the oceanographic context, cells at Diel 1 and 2 received less light and were more deeply mixed than cells at Diel 3, causing a dampening of the diel response. These results highlight that phytoplankton in the SAZ is regulated by the physical processes of mixing and light provision, but short-term diel effects on maximum quantum yield of PSII and photoprotective pigments may not propagate to changes in carbon fixation, particularly when cells are nutrient replete. If however, the more stratified eastern SAZ (which had the greatest diel responses) is indicative of how the SAZ region might respond to climate change, then diel effects may become more prominent in the future. [Copyright &y& Elsevier]

Abstract: In situ primary productivity (PP) in the Sub-Antarctic Zone (SAZ) and the Polar Frontal Zone (PFZ) south of Australia was estimated using fast repetition rate fluorometry (FRRF). FRRF-derived PP at Process station 3 (P3) southeast of Tasmania (46°S, 153°E) were higher than P1 in the southwest of Tasmania (46°S, 140°E) and P2 in the Polar Frontal Zone (54°S, 146°E). The FRRF-derived PP rates were well correlated with 14C-uptake rates from one-hour incubations (r 2=0.85, slope=1.23±0.05, p<0.01, n=85) but the relationship between both methods differed vertically and spatially. There was a linear relationship between FRRF-based PP and 14C-based PP under light-limited conditions in deeper waters. Under light-saturated conditions near the surface (0–45m), the relationship was less clear. This was likely associated with the effects of physiological processes such as cyclic electron flow and the Mehler reaction, which are stimulated at high irradiance. Our results indicate that FRRF can be used to estimate photosynthesis rates in the SAZ and PFZ but to derive an accurate estimation of C-fixation requires a detailed understanding of the physiological properties of the cells and their response to oceanographic parameters under different environmental conditions. [Copyright &y& Elsevier]

Background and aims: Medicago sativa L. is widely grown in southern Australia, but is poorly adapted to dry, hot summers. This study aimed to identify perennial herbaceous legumes with greater resistance to drought stress and explore their adaptive strategies. Methods: Ten herbaceous perennial legume species/accessions were grown in deep pots in a sandy, low-phosphorus field soil in a glasshouse. Drought stress was imposed by ceasing to water. A companion M. sativa plant in each pot minimised differences in leaf area and water consumption among species. Plants were harvested when stomatal conductance of stressed plants decreased to around 10% of well watered plants. Results: A range of responses to drought stress were identified, including: reduced shoot growth; leaf curling; thicker pubescence on leaves and stems; an increased root:shoot ratio; an increase, decrease or no change in root distribution with depth; reductions in specific leaf area or leaf water potential; and osmotic adjustment. The suite of changes differed substantially among species and, less so, among accessions. Conclusions: The inter- and intra-specific variability of responses to drought-stress in the plants examined suggests a wide range of strategies are available in perennial legumes to cope with drying conditions, and these could be harnessed in breeding/selection programs. [ABSTRACT FROM AUTHOR]

ABSTRACT A critical component of photosynthetic capacity is the conductance of CO2 from intercellular airspaces to the sites of CO2 fixation in the stroma of chloroplasts, termed mesophyll conductance ( gm). Leaf anatomy has been identified as an important determinant of gm. There are few studies of the temperature response of gm and none has examined the implications of leaf anatomy. Hence, we compared a cultivar of Oryza sativa with two wild Oryza relatives endemic to the hot northern savannah of Australia, namely Oryza meridionalis and Oryza australiensis. All three species had similar leaf anatomical properties, except that the wild relatives had significantly thicker mesophyll cell walls than O. sativa. Thicker mesophyll cell walls in the wild rice species are likely to have contributed to the reduction in gm, which was associated with a greater drawdown of CO2 into chloroplasts ( Ci- Cc) compared with O. sativa. Mesophyll conductance increased at higher temperatures, whereas the rate of CO2 assimilation was relatively stable between 20 and 40 °C. Consequently, Ci- Cc decreased for all three species as temperature increased. [ABSTRACT FROM AUTHOR]

The temporal pattern of river metabolism was estimated for high-order rivers (5--7th) in the Daly watershed, tropical Australia, during the dry season (May--October) when discharge was supplied predominantly by groundwater. Rates of photosynthesis ( P) and respiration ( R) were calculated at 4 sites using the open-channel method based on a model of the river's O2 budget and measured diurnal cycles of dissolved O2 concentrations and temperatures. The rivers were shallow (average depth == 0.8  m), clear (1--2 NTU), and had low concentrations of nutrients (≤≤15  µµg/L soluble N and P at most sites) and generally open canopy. At the reach scale, P was limited by light with no evidence of light saturation. An increase in primary producer biomass over the dry season probably underpinned an approximate doubling of P at the 4 sites over the dry season, but increased water temperatures would have contributed, too. P (0.1--4.6  g O2 m−−2  d−−1) in the Daly watershed was similar to rates in a shaded tropical Puerto Rican stream and some temperate rivers but was lower than in nutrient-enriched temperate rivers. We surmise that most P resulted in production of dissolved organic C (DOC), rather than growth of primary producer biomass, which was nutrient limited. R exceeded P ( P/ R ≈≈ 0.5), and increased approximately linearly with P ( r2 == 0.79--0.99) over the dry season with no statistically significant difference among sites. The similar environmental setting of the 4 sites underpinned their similar temporal pattern of metabolism. Bacterial metabolism of photosynthetically produced DOC (PDOC) could partially explain the tight coupling of R and P but could not account for the river's overall net heterotrophy. The priming effect of bacterial degradation of labile PDOC to increase the mineralization of recalcitrant DOC (e.g., humic acids) provides an explanation for the river's heterotrophy and tight coupling between P and R. [ABSTRACT FROM AUTHOR]

Abstract: Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P n /g s ) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions. [Copyright &y& Elsevier]

Abstract: Partial defoliation has been shown to affect the water relations and transpiration (gas exchange) of plants. Over one growing season, the water relations in response to partial (∼45%) defoliation were examined in four-year-old Eucalyptus globulus trees in southern Australia. Daily maximum transpiration rates (E max), maximum canopy conductance (), and diurnal patterns of tree water-use were measured over a period of 215 days using the heat-pulse technique in adjacent control (non-defoliated) and defoliated trees. Sap-flux measurements were used to estimate canopy conductance and soil-to-leaf hydraulic conductance (K P); leaf water potential (Ψ) and climate data were also collected. Following the removal of the upper canopy layer, defoliated trees exhibited compensatory responses in transpiration rate and canopy conductance of the remaining foliage. Defoliated E. globulus had similar predawn but higher midday Ψ l, transpiration rates (E), canopy conductance (G C) and K P compared to the non-defoliated controls, possibly in response to increased water supply per unit leaf area demonstrated by higher midday Ψ l. Higher E in defoliated E. globulus trees was the result of higher G C in the morning and early afternoon. This paper also incorporates the cumulative effect of defoliation, in a phenomenological model of maximum canopy conductance of E. globulus. These results contribute to a mechanistic understanding of plant responses to defoliation, in particular the often observed up-regulation of photosynthesis that also occurs in response to defoliation. [ABSTRACT FROM AUTHOR]

Abstract: Steady state and dynamic responses of two tree fern species of contrasting origins, Dicksonia antarctica (of Gondwanan origin) and Cyathea australis (Pan-tropical), were studied over two consecutive years under field conditions in a wet sclerophyll forest of south-east Australia. Irrespective of their different origins, there were no significant differences in photosynthetic performance between the two species. Growth irradiance and leaf temperature, but not plant water status, was significantly related to photosynthetic and morphological traits. At a common leaf temperature, maximum light-use efficiency of photosystem II (F v/F m) was significantly lower in winter than in summer, suggesting some limitation to PSII efficiency potentially associated with cold winter mornings. Both species displayed seasonal acclimation in a number of measured photosynthetic parameters and frond traits (i.e. F v/F m, A sat, g s, N A, total chlorophyll, SLA). Acclimation of stomatal density to spatial variation in growth irradiance seemed limited in both species, although stomatal pattern differed between species. Because there were no significant differences between the two species in photosynthetic parameters, both species can be described by common carbon gain and water use models at the leaf scale. [ABSTRACT FROM AUTHOR]

Exotic and invasive woody vines are major environmental weeds of riparian areas, rainforest communities and remnant natural vegetation in coastal eastern Australia, where they smother standing vegetation, including large trees, and cause canopy collapse. We investigated, through glasshouse resource manipulative experiments, the ecophysiological traits that might facilitate faster growth, better resource acquisition and/or utilization and thus dominance of four exotic and invasive vines of South East Queensland, Australia, compared with their native counterparts. Relative growth rate was not significantly different between the two groups but water use efficiency (WUE) was higher in the native species while the converse was observed for light use efficiency (quantum efficiency, AQE) and maximum photosynthesis on a mass basis ( ). The invasive species, as a group, also exhibited higher respiration load, higher light compensation point and higher specific leaf area. There were stronger correlations of leaf traits and greater structural (but not physiological) plasticity in invasive species than in their native counterparts. The scaling coefficients of resource use efficiencies (WUE, AQE and respiration efficiency) as well as those of fitness (biomass accumulated) versus many of the performance traits examined did not differ between the two species-origin groups, but there were indications of significant shifts in elevation (intercept values) and shifts along common slopes in many of these relationships – signalling differences in carbon economy (revenue returned per unit energy invested) and/or resource usage. Using ordination and based on 14 ecophysiological attributes, a fair level of separation between the two groups was achieved (51.5% explanatory power), with AQE, light compensation point, respiration load, WUE, specific leaf area and leaf area ratio, in decreasing order, being the main drivers. This study suggests similarity in trait plasticity, especially for physiological traits, but there appear to be fundamental differences in carbon economy and resource conservation between native and invasive vine species. [ABSTRACT FROM AUTHOR]