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The tiller inhibition (tin) and Reduced height (Rht) genes strongly influence the carbon partitioning and architecture of wheat shoots, but their effects on the energy economy of roots have not been examined in detail. We examined multiple root traits in three sets of near‐isogenic wheat lines (NILs) that differ in the tin gene or various dwarfing gene alleles (Rht‐B1b, Rht‐D1b, Rht‐B1c and Rht‐B1b + Rht‐D1b) to determine their effects on root structure, anatomy and carbon allocation. The tin gene resulted in fewer tillers but more costly roots in an extreme tin phenotype with a Banks genetic background due to increases in root‐to‐shoot ratio, total root length, and whole root respiration. However, this effect depended on the genetic background as tin caused both smaller shoots and roots in a different genetic background. The semi‐dwarf gene Rht‐B1b caused few changes to the root structure, whereas Rht‐D1b, Rht‐B1c and the double dwarf (Rht‐B1b + Rht‐D1b) decreased the root biomass. Rht‐B1c reduced the energy cost of roots by increasing specific root length, increasing the volume of cortical aerenchyma and by reducing root length, number, and biomass without affecting the root‐to‐shoot ratio. This work informs researchers using tin and Rht genes how to modify root system architecture to suit specific environments. [ABSTRACT FROM AUTHOR]

Summary: Heat stress interrupts physiological thermostability and triggers biochemical responses that are essential for plant survival. However, there is limited knowledge on the speed plants adjust to heat in hours and days, and which adjustments are crucial.Tropical–subtropical rainforest tree species (Polyscias elegans) were heated at 40°C for 5 d, before returning to 25°C for 13 d of recovery. Leaf heat tolerance was quantified using the temperature at which minimal chl a fluorescence sharply rose (Tcrit). Tcrit, metabolites, heat shock protein (HSP) abundance and membrane lipid fatty acid (FA) composition were quantified.Tcrit increased by 4°C (48–52°C) within 2 h of 40°C exposure, along with rapid accumulation of metabolites and HSPs. By contrast, it took > 2 d for FA composition to change. At least 2 d were required for Tcrit, HSP90, HSP70 and FAs to return to prestress levels.The results highlight the multi‐faceted response of P. elegans to heat stress, and how this response varies over the scale of hours to days, culminating in an increased level of photosynthetic heat tolerance. These responses are important for survival of plants when confronted with heat waves amidst ongoing global climate change. [ABSTRACT FROM AUTHOR]

Summary: Leaf dark respiration (Rd) acclimates to environmental changes. However, the magnitude, controls and time scales of acclimation remain unclear and are inconsistently treated in ecosystem models.We hypothesized that Rd and Rubisco carboxylation capacity (Vcmax) at 25°C (Rd,25, Vcmax,25) are coordinated so that Rd,25 variations support Vcmax,25 at a level allowing full light use, with Vcmax,25 reflecting daytime conditions (for photosynthesis), and Rd,25/Vcmax,25 reflecting night‐time conditions (for starch degradation and sucrose export). We tested this hypothesis temporally using a 5‐yr warming experiment, and spatially using an extensive field‐measurement data set. We compared the results to three published alternatives: Rd,25 declines linearly with daily average prior temperature; Rd at average prior night temperatures tends towards a constant value; and Rd,25/Vcmax,25 is constant.Our hypothesis accounted for more variation in observed Rd,25 over time (R2 = 0.74) and space (R2 = 0.68) than the alternatives. Night‐time temperature dominated the seasonal time‐course of Rd, with an apparent response time scale of c. 2 wk. Vcmax dominated the spatial patterns.Our acclimation hypothesis results in a smaller increase in global Rd in response to rising CO2 and warming than is projected by the two of three alternative hypotheses, and by current models. [ABSTRACT FROM AUTHOR]

"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 spanning 528 species from 67 sites. We tested the hypotheses that plants on relatively cold or dry sites, or on relatively more fertile sites, would typically operate at greater CO2 drawdown (lower ratio of leaf internal to ambient CO2, Ci:Ca) during light‐saturated photosynthesis, and at higher leaf N per area (Narea) and higher carboxylation capacity (Vcmax 25) for a given rate of stomatal conductance to water vapour, gsw. These results would be indicative of plants having relatively higher water costs than nutrient costs. In general, our hypotheses were supported. Soil total phosphorus (P) concentration and (more weakly) soil pH exerted positive effects on the Narea–gsw and Vcmax 25–gsw slopes, and negative effects on Ci:Ca. The P effect strengthened when the effect of climate was removed via partial regression. We observed similar trends with increasing soil cation exchange capacity and clay content, which affect soil nutrient availability, and found that soil properties explained similar amounts of variation in the focal traits as climate did. Although climate typically explained more trait variation than soil did, together they explained up to 52% of variation in the slope relationships and soil properties explained up to 30% of the variation in individual traits. Soils influenced photosynthetic traits as well as their coordination. In particular, the influence of soil P likely reflects the Australia's geologically ancient low‐relief landscapes with highly leached soils. Least‐cost theory provides a valuable framework for understanding trade‐offs between resource costs and use in plants, including limiting soil nutrients. [ABSTRACT FROM AUTHOR]

Summary: The rate with which crop yields per hectare increase each year is plateauing at the same time that human population growth and other factors increase food demand. Increasing yield potential (Yp) of crops is vital to address these challenges. In this review, we explore a component of Yp that has yet to be optimised – that being improvements in the efficiency with which light energy is converted into biomass (εc) via modifications to CO2 fixed per unit quantum of light (α), efficiency of respiratory ATP production (εprod) and efficiency of ATP use (εuse). For α, targets include changes in photoprotective machinery, ribulose bisphosphate carboxylase/oxygenase kinetics and photorespiratory pathways. There is also potential for εprod to be increased via targeted changes to the expression of the alternative oxidase and mitochondrial uncoupling pathways. Similarly, there are possibilities to improve εuse via changes to the ATP costs of phloem loading, nutrient uptake, futile cycles and/or protein/membrane turnover. Recently developed high‐throughput measurements of respiration can serve as a proxy for the cumulative energy cost of these processes. There are thus exciting opportunities to use our growing knowledge of factors influencing the efficiency of photosynthesis and respiration to create a step‐change in yield potential of globally important crops. [ABSTRACT FROM AUTHOR]

Leaf dry mass per unit area (LMA), carboxylation capacity (Vcmax) and leaf nitrogen per unit area (Narea) and mass (Nmass) are key traits for plant functional ecology and ecosystem modelling. There is however no consensus about how these traits are regulated, or how they should be modelled. Here we confirm that observed leaf nitrogen across species and sites can be estimated well from observed LMA and Vcmax at 25°C (Vcmax25). We then test the hypothesis that global variations of both quantities depend on climate variables in specific ways that are predicted by leaf‐level optimality theory, thus allowing both Narea to be predicted as functions of the growth environment.A new global compilation of field measurements was used to quantify the empirical relationships of leaf N to Vcmax25 and LMA. Relationships of observed Vcmax25 and LMA to climate variables were estimated, and compared to independent theoretical predictions of these relationships. Soil effects were assessed by analysing biases in the theoretical predictions.LMA was the most important predictor of Narea (increasing) and Nmass (decreasing). About 60% of global variation across species and sites in observed Narea, and 31% in Nmass, could be explained by observed LMA and Vcmax25. These traits, in turn, were quantitatively related to climate variables, with significant partial relationships similar or indistinguishable from those predicted by optimality theory. Predicted trait values explained 21% of global variation in observed site‐mean Vcmax25, 43% in LMA and 31% in Narea. Predicted Vcmax25 was biased low on clay‐rich soils but predicted LMA was biased high, with compensating effects on Narea. Narea was overpredicted on organic soils.Synthesis. Global patterns of variation in observed site‐mean Narea can be explained by climate‐induced variations in optimal Vcmax25 and LMA. Leaf nitrogen should accordingly be modelled as a consequence (not a cause) of Vcmax25 and LMA, both being optimized to the environment. Nitrogen limitation of plant growth would then be modelled principally via whole‐plant carbon allocation, rather than via leaf‐level traits. Further research is required to better understand and model the terrestrial nitrogen and carbon cycles and their coupling. [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]

Our understanding of the regulation of respiration in C4 plants, where mitochondria play different roles in the different types of C4 photosynthetic pathway, remains limited. We examined how leaf dark respiration rates (Rdark), in the presence and absence of added malate, vary in monocots representing the three classical biochemical types of C4 photosynthesis (NADP‐ME, NAD‐ME and PCK) using intact leaves and extracted bundle sheath strands. In particular, we explored to what extent rates of Rdark are associated with mitochondrial number, volume and ultrastructure. Based on examination of a single species per C4 type, we found that the respiratory response of NAD‐ME and PCK type bundle sheath strands to added malate was associated with differences in mitochondrial number, volume, and/or ultrastructure, while NADP‐ME type bundle sheath strands did not respond to malate addition. In general, mitochondrial traits reflected the contributions mitochondria make to photosynthesis in the three C4 types. However, despite the obvious differences in mitochondrial traits, no clear correlation was observed between these traits and Rdark. We suggest that Rdark is primarily driven by cellular maintenance demands and not mitochondrial composition per se, in a manner that is somewhat independent of mitochondrial organic acid cycling in the light. SUMMARY STATEMENT: We found distinct anatomical, ultrastructural and functional differences in mitochondria of leaves using the three classical biochemical types of C4 photosynthesis. Such differences reflect the roles of mitochondria in photosynthesis. However, we found no clear correlation between mitochondrial composition and leaf dark respiration rates, suggesting leaf dark respiration is likely driven by cellular maintenance demands but not mitochondrial composition. [ABSTRACT FROM AUTHOR]

Growing at either 15 or 25°C, roots of Arabidopsis thaliana, Columbia accession, produce cells at the same rate and have growth zones of the same length. To determine whether this constancy is related to energetics, we measured oxygen uptake by means of a vibrating oxygen‐selective electrode. Concomitantly, the spatial distribution of elongation was measured kinematically, delineating meristem and elongation zone. All seedlings were germinated, grown, and measured at a given temperature (15 or 25°C). Columbia was compared to lines where cell production rate roughly doubles between 15 and 25°C: Landsberg and two Columbia mutants, er‐105 and ahk3‐3. For all genotypes and temperatures, oxygen uptake rate at any position was highest at the root cap, where mitochondrial density was maximal, based on the fluorescence of a reporter. Uptake rate declined through the meristem to plateau within the elongation zone. For oxygen uptake rate integrated over a zone, the meristem had steady‐state Q10 values ranging from 0.7 to 2.1; by contrast, the elongation zone had values ranging from 2.6 to 3.3, implying that this zone exerts a greater respiratory demand. These results highlight a substantial energy consumption by the root cap, perhaps helpful for maintaining hypoxia in stem cells, and suggest that rapid elongation is metabolically more costly than is cell division. [ABSTRACT FROM AUTHOR]

Simulations of the land surface carbon cycle typically compress functional diversity into a small set of plant functional types (PFT), with parameters defined by the average value of measurements of functional traits. In most earth system models, all wild plant life is represented by between five and 14 PFTs and a typical grid cell (≈100 × 100 km) may contain a single PFT. Model logic applied to this coarse representation of ecological functional diversity provides a reasonable proxy for the carbon cycle, but does not capture the non‐linear influence of functional traits on productivity. Here we show through simulations using the Energy Exascale Land Surface Model in 15 diverse terrestrial landscapes, that better accounting for functional diversity markedly alters predicted total carbon uptake. The shift in carbon uptake is as great as 30% and 10% in boreal and tropical regions, respectively, when compared to a single PFT parameterized with the trait means. The traits that best predict gross primary production vary based on vegetation phenology, which broadly determines where traits fall within the global distribution. Carbon uptake is more closely associated with specific leaf area for evergreen PFTs and the leaf carbon to nitrogen ratio in deciduous PFTs. Plain Language Summary: Plants play a critical role in the global carbon cycle, and diversity has been shown to influence vegetation productivity. However, when the land surface is simulated in a global model all wild plant life is reduced to a small number of plant functional types. Here we estimate how incorporating diversity influences ecosystem carbon uptake in 15 globe spanning landscapes. We find that diversity has a strong influence on modeled productivity, particularly in the arctic and tropics. Further, we find that whether plants shed their leaves annually has a strong influence on where traits fall within the global distribution and thus how traits and productivity interact. Key Points: We implemented distributions of leaf economic spectrum traits in a land surface model in 15 diverse landscapesTrait variation has a substantial influence on gross primary production (GPP)Phenology plays a key role in guiding where traits fall within the global trait distribution and hence trait‐GPP relationships [ABSTRACT FROM AUTHOR]

Summary: C4 photosynthesis involves a series of biochemical and anatomical traits that significantly improve plant productivity under conditions that reduce the efficiency of C3 photosynthesis. We explore how evolution of the three classical biochemical types of C4 photosynthesis (NADP‐ME, NAD‐ME and PCK types) has affected the functions and properties of mitochondria. Mitochondria in C4 NAD‐ME and PCK types play a direct role in decarboxylation of metabolites for C4 photosynthesis. Mitochondria in C4 PCK type also provide ATP for C4 metabolism, although this role for ATP provision is not seen in NAD‐ME type. Such involvement has increased mitochondrial abundance/size and associated enzymatic capacity, led to changes in mitochondrial location and ultrastructure, and altered the role of mitochondria in cellular carbon metabolism in the NAD‐ME and PCK types. By contrast, these changes in mitochondrial properties are absent in the C4 NADP‐ME type and C3 leaves, where mitochondria play no direct role in photosynthesis. From an eco‐physiological perspective, rates of leaf respiration in darkness vary considerably among C4 species but does not differ systematically among the three C4 types. This review outlines further mitochondrial research in key areas central to the engineering of the C4 pathway into C3 plants and to the understanding of variation in rates of C4 dark respiration. [ABSTRACT FROM AUTHOR]

Climate change and future warming will significantly affect crop yield. The capacity of crops to dynamically adjust physiological processes (i.e., acclimate) to warming might improve overall performance. Understanding and quantifying the degree of acclimation in field crops could ensure better parameterization of crop and Earth System models and predictions of crop performance. We hypothesized that for field‐grown wheat, when measured at a common temperature (25°C), crops grown under warmer conditions would exhibit acclimation, leading to enhanced crop performance and yield. Acclimation was defined as (a) decreased rates of net photosynthesis at 25°C (A25) coupled with lower maximum carboxylation capacity (Vcmax25), (b) reduced leaf dark respiration at 25°C (both in terms of O2 consumption Rdark_O225 and CO2 efflux Rdark_CO225) and (c) lower Rdark_CO225 to Vcmax25 ratio. Field experiments were conducted over two seasons with 20 wheat genotypes, sown at three different planting dates, to test these hypotheses. Leaf‐level CO2‐based traits (A25, Rdark_CO225 and Vcmax25) did not show the classic acclimation responses that we hypothesized; by contrast, the hypothesized changes in Rdark_O2 were observed. These findings have implications for predictive crop models that assume similar temperature response among these physiological processes and for predictions of crop performance in a future warmer world. In field‐grown wheat, leaf‐level CO2‐based traits (photosynthesis, carboxylation capacity and respiration measured at 25°C) did not exhibit classic acclimation responses to warming generated by varying time of sowing; by contrast, O2‐based respiration did. [ABSTRACT FROM AUTHOR]

Mitochondrial respiration (R) is central to plant physiology and responds dynamically to daily short‐term temperature changes. In the longer‐term, changes in energy demand and membrane fluidity can decrease leaf R at a common temperature and increase the temperature at which leaf R peaks (Tmax). However, leaf R functionality is more susceptible to short‐term heatwaves. Catalysis increases with rising leaf temperature, driving faster metabolism and leaf R demand, despite declines in photosynthesis restricting assimilate supply and growth. Proteins denature as temperatures increase further, adding to maintenance costs. Excessive heat also inactivates respiratory enzymes, with a concomitant limitation on the capacity of the R system. These competing push‐and‐pull factors are responsible for the diminishing acceleration in leaf R rate as temperature rises. Under extreme heat, membranes become overly fluid, and enzymes such as the cytochrome c oxidase are impaired. Such changes can lead to over‐reduction of the energy system culminating in reactive oxygen species production. This ultimately leads to the total breakdown of leaf R, setting the limit of leaf survival. Understanding the heat stress responses of leaf R is imperative, given the continued rise in frequency and intensity of heatwaves and the importance of R for plant fitness and survival. We explore the response of plant leaf respiration to heatwaves. Interconnections between assimilate use, protein activity and stability, and membrane integrity emerge as the main influences on leaf respiration, ultimately setting the upper thermal limit of respiration and plant survival. [ABSTRACT FROM AUTHOR]

Kok effect, day respiration, mitochondria, photorespiration, photosynthesis Keywords: day respiration; Kok effect; mitochondria; photorespiration; photosynthesis EN day respiration Kok effect mitochondria photorespiration photosynthesis 5 10 6 03/04/21 20210401 NES 210401 Leaf respiration plays a key role in plant primary production due to its roles in determining rates of daily net carbon gain, nutrient acquisition, and growth. (2017) did not reveal a close relationship between I R i SB light sb and I R i SB dark sb , with I R i SB light sb < I R i SB dark sb in 84% of cases and I R i SB light sb > I R i SB dark sb in 16% of cases. [Extracted from the article]

Summary: Short‐term temperature response curves of leaf dark respiration (R–T) provide insights into a critical process that influences plant net carbon exchange. This includes how respiratory traits acclimate to sustained changes in the environment.Our study analysed 860 high‐resolution R–T (10–70°C range) curves for: (a) 62 evergreen species measured in two contrasting seasons across several field sites/biomes; and (b) 21 species (subset of those sampled in the field) grown in glasshouses at 20°C : 15°C, 25°C : 20°C and 30°C : 25°C, day : night.In the field, across all sites/seasons, variations in R25 (measured at 25°C) and the leaf T where R reached its maximum (Tmax) were explained by growth T (mean air‐T of 30‐d before measurement), solar irradiance and vapour pressure deficit, with growth T having the strongest influence. R25 decreased and Tmax increased with rising growth T across all sites and seasons with the single exception of winter at the cool‐temperate rainforest site where irradiance was low. The glasshouse study confirmed that R25 and Tmax thermally acclimated.Collectively, the results suggest: (1) thermal acclimation of leaf R is common in most biomes; and (2) the high T threshold of respiration dynamically adjusts upward when plants are challenged with warmer and hotter climates. [ABSTRACT FROM AUTHOR]

Summary: Leaf respiration in the dark (Rdark) is often measured at a single time during the day, with hot‐acclimation lowering Rdark at a common measuring temperature. However, it is unclear whether the diel cycle influences the extent of thermal acclimation of Rdark, or how temperature and time of day interact to influence respiratory metabolites.To examine these issues, we grew rice under 25°C : 20°C, 30°C : 25°C and 40°C : 35°C day : night cycles, measuring Rdark and changes in metabolites at five time points spanning a single 24‐h period.Rdark differed among the treatments and with time of day. However, there was no significant interaction between time and growth temperature, indicating that the diel cycle does not alter thermal acclimation of Rdark. Amino acids were highly responsive to the diel cycle and growth temperature, and many were negatively correlated with carbohydrates and with organic acids of the tricarboxylic acid (TCA) cycle. Organic TCA intermediates were significantly altered by the diel cycle irrespective of growth temperature, which we attributed to light‐dependent regulatory control of TCA enzyme activities.Collectively, our study shows that environmental disruption of the balance between respiratory substrate supply and demand is corrected for by shifts in TCA‐dependent metabolites. [ABSTRACT FROM AUTHOR]

Summary: We used a widely distributed tree Eucalyptus camaldulensis subsp. camaldulensis to partition intraspecific variation in leaf functional traits to genotypic variation and phenotypic plasticity. We examined if genotypic variation is related to the climate of genotype provenance and whether phenotypic plasticity maintains performance in a changing environment.Ten genotypes from different climates were grown in a common garden under watering treatments reproducing the wettest and driest edges of the subspecies' distribution. We measured functional traits reflecting leaf metabolism and associated with growth (respiration rate, nitrogen and phosphorus concentrations, and leaf mass per area) and performance proxies (aboveground biomass and growth rate) each season over a year.Genotypic variation contributed substantially to the variation in aboveground biomass but much less in growth rate and leaf traits. Phenotypic plasticity was a large source of the variation in leaf traits and performance proxies and was greater among sampling dates than between watering treatments. The variation in leaf traits was weakly correlated to performance proxies, and both were unrelated to the climate of genotype provenance.Intraspecific variation in leaf traits arises similarly among genotypes in response to seasonal environmental variation, instead of long‐term water availability or climate of genotype provenance. [ABSTRACT FROM AUTHOR]

Plant respiration is an important contributor to the proposed positive global carbon‐cycle feedback to climate change. However, as a major component, leaf mitochondrial ('dark') respiration (Rd) differs among species adapted to contrasting environments and is known to acclimate to sustained changes in temperature. No accepted theory explains these phenomena or predicts its magnitude. Here we propose that the acclimation of Rd follows an optimal behaviour related to the need to maintain long‐term average photosynthetic capacity (Vcmax) so that available environmental resources can be most efficiently used for photosynthesis. To test this hypothesis, we extend photosynthetic co‐ordination theory to predict the acclimation of Rd to growth temperature via a link to Vcmax, and compare predictions to a global set of measurements from 112 sites spanning all terrestrial biomes. This extended co‐ordination theory predicts that field‐measured Rd and Vcmax accessed at growth temperature (Rd,tg and Vcmax,tg) should increase by 3.7% and 5.5% per degree increase in growth temperature. These acclimated responses to growth temperature are less steep than the corresponding instantaneous responses, which increase 8.1% and 9.9% per degree of measurement temperature for Rd and Vcmax respectively. Data‐fitted responses proof indistinguishable from the values predicted by our theory, and smaller than the instantaneous responses. Theory and data are also shown to agree that the basal rates of both Rd and Vcmax assessed at 25°C (Rd,25 and Vcmax,25) decline by ~4.4% per degree increase in growth temperature. These results provide a parsimonious general theory for Rd acclimation to temperature that is simpler—and potentially more reliable—than the plant functional type‐based leaf respiration schemes currently employed in most ecosystem and land‐surface models. [ABSTRACT FROM AUTHOR]

To further our understanding of how sustained changes in temperature affect the carbon economy of rice (Oryza sativa), hydroponically grown plants of the IR64 cultivar were developed at 30°C/25°C (day/night) before being shifted to 25/20°C or 40/35°C. Leaf messenger RNA and protein abundance, sugar and starch concentrations, and gas‐exchange and elongation rates were measured on preexisting leaves (PE) already developed at 30/25°C or leaves newly developed (ND) subsequent to temperature transfer. Following a shift in growth temperature, there was a transient adjustment in metabolic gene transcript abundance of PE leaves before homoeostasis was reached within 24 hr, aligning with Rdark (leaf dark respiratory CO2 release) and An (net CO2 assimilation) changes. With longer exposure, the central respiratory protein cytochrome c oxidase (COX) declined in abundance at 40/35°C. In contrast to Rdark, An was maintained across the three growth temperatures in ND leaves. Soluble sugars did not differ significantly with growth temperature, and growth was fastest with extended exposure at 40/35°C. The results highlight that acclimation of photosynthesis and respiration is asynchronous in rice, with heat‐acclimated plants exhibiting a striking ability to maintain net carbon gain and growth when exposed to heat‐wave temperatures, even while reducing investment in energy‐conserving respiratory pathways. Leaf respiration and photosynthesis in rice (Oryza sativa L.) shows asynchronous acclimation capacity in favour of photosynthesis. Heat acclimation reduced the protein abundance of the respiratory protein cytochrome c oxidase (COX), despite respiration and growth being stimulated. [ABSTRACT FROM AUTHOR]

Aim: Plant trait databases often contain traits that are correlated, but for whom direct (undirected statistical dependency) and indirect (mediated by other traits) connections may be confounded. The confounding of correlation and connection hinders our understanding of plant strategies, and how these vary among growth forms and climate zones. We identified the direct and indirect connections across plant traits relevant to competition, resource acquisition and reproductive strategies using a global database and explored whether connections within and between traits from different tissue types vary across climates and growth forms. Location: Global. Major taxa studied: Plants. Time period: Present. Methods: We used probabilistic graphical models and a database of 10 plant traits (leaf area, specific leaf area, mass‐ and area‐based leaf nitrogen and phosphorous content, leaf life span, plant height, stem specific density and seed mass) with 16,281 records to describe direct and indirect connections across woody and non‐woody plants across tropical, temperate, arid, cold and polar regions. Results: Trait networks based on direct connections are sparser than those based on correlations. Land plants had high connectivity across traits within and between tissue types; leaf life span and stem specific density shared direct connections with all other traits. For both growth forms, two groups of traits form modules of more highly connected traits; one related to resource acquisition, the other to plant architecture and reproduction. Woody species had higher trait network modularity in polar compared to temperate and tropical climates, while non‐woody species did not show significant differences in modularity across climate regions. Main conclusions: Plant traits are highly connected both within and across tissue types, yet traits segregate into persistent modules of traits. Variation in the modularity of trait networks suggests that trait connectivity is shaped by prevailing environmental conditions and demonstrates that plants of different growth forms use alternative strategies to cope with local conditions. [ABSTRACT FROM AUTHOR]

Greater availability of leaf dark respiration (Rdark) data could facilitate breeding efforts to raise crop yield and improve global carbon cycle modelling. However, the availability of Rdark data is limited because it is cumbersome, time consuming, or destructive to measure. We report a non‐destructive and high‐throughput method of estimating Rdark from leaf hyperspectral reflectance data that was derived from leaf Rdark measured by a destructive high‐throughput oxygen consumption technique. We generated a large dataset of leaf Rdark for wheat (1380 samples) from 90 genotypes, multiple growth stages, and growth conditions to generate models for Rdark. Leaf Rdark (per unit leaf area, fresh mass, dry mass or nitrogen, N) varied 7‐ to 15‐fold among individual plants, whereas traits known to scale with Rdark, leaf N, and leaf mass per area (LMA) only varied twofold to fivefold. Our models predicted leaf Rdark, N, and LMA with r2 values of 0.50–0.63, 0.91, and 0.75, respectively, and relative bias of 17–18% for Rdark and 7–12% for N and LMA. Our results suggest that hyperspectral model prediction of wheat leaf Rdark is largely independent of leaf N and LMA. Potential drivers of hyperspectral signatures of Rdark are discussed. Measuring leaf dark respiration is either slow and cumbersome or rapid and destructive. We used light reflected from wheat leaf surfaces to rapidly and non‐destructively estimate wheat respiration. Predictions were largely independent of the relationships between leaf dark respiration and leaf nitrogen or leaf mass per unit area. This finding highlights the potential for rapid non‐invasive monitoring of various aspects of leaf energy metabolism in wheat. [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]

Understanding forest tree responses to climate warming and heatwaves is important for predicting changes in tree species diversity, forest C uptake, and vegetation–climate interactions. Yet, tree species differences in heatwave tolerance and their plasticity to growth temperature remain poorly understood. In this study, populations of four Eucalyptus species, two with large range sizes and two with comparatively small range sizes, were grown under two temperature treatments (cool and warm) before being exposed to an equivalent experimental heatwave. We tested whether the species with large and small range sizes differed in heatwave tolerance, and whether trees grown under warmer temperatures were more tolerant of heatwave conditions than trees grown under cooler temperatures. Visible heatwave damage was more common and severe in the species with small rather than large range sizes. In general, species that showed less tissue damage maintained higher stomatal conductance, lower leaf temperatures, larger increases in isoprene emissions, and less photosynthetic inhibition than species that showed more damage. Species exhibiting more severe visible damage had larger increases in heat shock proteins (HSPs) and respiratory thermotolerance (Tmax). Thus, across species, increases in HSPs and Tmax were positively correlated, but inversely related to increases in isoprene emissions. Integration of leaf gas‐exchange, isoprene emissions, proteomics, and respiratory thermotolerance measurements provided new insight into mechanisms underlying variability in tree species heatwave tolerance. Importantly, warm‐grown seedlings were, surprisingly, more susceptible to heatwave damage than cool‐grown seedlings, which could be associated with reduced enzyme concentrations in leaves. We conclude that species with restricted range sizes, along with trees growing under climate warming, may be more vulnerable to heatwaves of the future. [ABSTRACT FROM AUTHOR]

ContentsSummary670I.Introduction671II.Principle 1 – Plant respiration performs three distinct functions673III.Principle 2 – Metabolic pathway flexibility underlies plant respiratory performance676IV.Principle 3 – Supply and demand interact over time to set plant respiration rate677V.Principle 4 – Plant respiratory acclimation involves adjustments in enzyme capacities679VI.Principle 5 – Respiration is a complex trait that helps to define, and is impacted by, plant lifestyle strategies680VII.Future directions680Acknowledgements682References682 Summary: Respiration is a core biological process that has important implications for the biochemistry, physiology, and ecology of plants. The study of plant respiration is thus conducted from several different perspectives by a range of scientific disciplines with dissimilar objectives, such as metabolic engineering, crop breeding, and climate‐change modelling. One aspect in common among the different objectives is a need to understand and quantify the variation in respiration across scales of biological organization. The central tenet of this review is that different perspectives on respiration can complement each other when connected. To better accommodate interdisciplinary thinking, we identify distinct mechanisms which encompass the variation in respiratory rates and functions across biological scales. The relevance of these mechanisms towards variation in plant respiration are explained in the context of five core principles: (1) respiration performs three distinct functions; (2) metabolic pathway flexibility underlies respiratory performance; (3) supply and demand interact over time to set respiration rates; (4) acclimation involves adjustments in enzyme capacities; and (5) respiration is a complex trait that helps to define, and is impacted by, plant lifestyle strategies. We argue that each perspective on respiration rests on these principles to varying degrees and that broader appreciation of how respiratory variation occurs can unite research across scales. [ABSTRACT FROM AUTHOR]

In many biomes, plants are subject to heatwaves, potentially causing irreversible damage to the photosynthetic apparatus. Field surveys have documented global, temperature-dependent patterns in photosynthetic heat tolerance (PHT); however, it remains unclear if these patterns reflect acclimation in PHT or inherent differences among species adapted to contrasting habitats. To address these unknowns, we quantified seasonal variations in Tcrit (high temperature where minimal chlorophyll-a fluorescence rises rapidly, reflecting disruption to photosystem II) in 62 species native to 6 sites from 5 thermally contrasting biomes across Australia. Tcrit and leaf fatty acid (FA) composition (important for membrane stability) were quantified in three temperaturecontrolled glasshouses in 20 of those species. Tcrit was greatest at hot field sites and acclimated seasonally (summer > winter, increasing on average 0.34 °C per °C increase in growth temperature). The glasshouse study showed that Tcrit was inherently higher in species from warmer habitats (increasing 0.16 °C per °C increase in origin annual mean maximum temperature) and acclimated to increasing growth temperature (0.24 °C °C-1). Variations in Tcrit were positively correlated with the relative abundance of saturated FAs, with FAs accounting for 40% of Tcrit variation. These results highlight the importance of both plastic adjustments and inherent differences determining contemporary continent-wide patterns in PHT. [ABSTRACT FROM AUTHOR]

Heatwaves are likely to increase in frequency and intensity with climate change, which may impair tree function and forest C uptake. However, we have little information regarding the impact of extreme heatwaves on the physiological performance of large trees in the field. Here, we grew Eucalyptus parramattensis trees for 1 year with experimental warming (+3°C) in a field setting, until they were greater than 6 m tall. We withheld irrigation for 1 month to dry the surface soils and then implemented an extreme heatwave treatment of 4 consecutive days with air temperatures exceeding 43°C, while monitoring whole-canopy exchange of CO2 and H2O, leaf temperatures, leaf thermal tolerance, and leaf and branch hydraulic status. The heatwave reduced midday canopy photosynthesis to near zero but transpiration persisted, maintaining canopy cooling. A standard photosynthetic model was unable to capture the observed decoupling between photosynthesis and transpiration at high temperatures, suggesting that climate models may underestimate a moderating feedback of vegetation on heatwave intensity. The heatwave also triggered a rapid increase in leaf thermal tolerance, such that leaf temperatures observed during the heatwave were maintained within the thermal limits of leaf function. All responses were equivalent for trees with a prior history of ambient and warmed (+3°C) temperatures, indicating that climate warming conferred no added tolerance of heatwaves expected in the future. This coordinated physiological response utilizing latent cooling and adjustment of thermal thresholds has implications for tree tolerance of future climate extremes as well as model predictions of future heatwave intensity at landscape and global scales. [ABSTRACT FROM AUTHOR]

Summary: Globally, trees originating from high‐rainfall tropical regions typically exhibit lower rates of light‐saturated net CO2 assimilation (A) compared with those from high‐rainfall temperate environments, when measured at a common temperature. One factor that has been suggested to contribute towards lower rates of A is lower mesophyll conductance. Using a combination of leaf gas exchange and carbon isotope discrimination measurements, we estimated mesophyll conductance (gm) of several Australian tropical and temperate wet‐forest trees, grown in a common environment. Maximum Rubisco carboxylation capacity, Vcmax, was obtained from CO2 response curves. gm and the drawdown of CO2 across the mesophyll were both relatively constant. Vcmax estimated on the basis of intercellular CO2 partial pressure, Ci, was equivalent to that estimated using chloroplastic CO2 partial pressure, Cc, using ‘apparent’ and ‘true’ Rubisco Michaelis–Menten constants, respectively Having ruled out gm as a possible factor in distorting variations in A between these tropical and temperate trees, attention now needs to be focused on obtaining more detailed information about Rubisco in these species. [ABSTRACT FROM AUTHOR]

Drought‐induced reduction of leaf gas exchange entails a complex regulation of the plant leaf metabolism. We used a combined molecular and physiological approach to understand leaf photosynthetic and respiratory responses of 2‐year‐old Quercus ilex seedlings to drought. Mild drought stress resulted in glucose accumulation while net photosynthetic CO2 uptake (Pn) remained unchanged, suggesting a role of glucose in stress signaling and/or osmoregulation. Simple sugars and sugar alcohols increased throughout moderate‐to‐very severe drought stress conditions, in parallel to a progressive decline in Pn and the quantum efficiency of photosystem II; by contrast, minor changes occurred in respiration rates until drought stress was very severe. At very severe drought stress, 2‐oxoglutarate dehydrogenase complex gene expression significantly decreased, and the abundance of most amino acids dramatically increased, especially that of proline and γ‐aminobutyric acid (GABA) suggesting enhanced protection against oxidative damage and a reorganization of the tricarboxylic cycle acid cycle via the GABA shunt. Altogether, our results point to Q. ilex drought tolerance being linked to signaling and osmoregulation by hexoses during early stages of drought stress, and enhanced protection against oxidative damage by polyols and amino acids under severe drought stress. [ABSTRACT FROM AUTHOR]

Abstract: Temperature is a crucial factor in determining the rates of ecosystem processes, for example, leaf respiration (R) – the flux of plant respired CO2 from leaves to the atmosphere. Generally, R increases exponentially with temperature and formulations such as the Arrhenius equation are widely used in earth system models. However, experimental observations have shown a consequential and consistent departure from an exponential increase in R. What are the principles that underlie these observed patterns? Here, we demonstrate that macromolecular rate theory (MMRT), based on transition state theory (TST) for enzyme‐catalyzed kinetics, provides a thermodynamic explanation for the observed departure and the convergent temperature response of R using a global database. Three meaningful parameters emerge from MMRT analysis: the temperature at which the rate of respiration would theoretically reach a maximum (the optimum temperature, Topt), the temperature at which the respiration rate is most sensitive to changes in temperature (the inflection temperature, Tinf) and the overall curvature of the log(rate) versus temperature plot (the change in heat capacity for the system, Δ C P ‡). On average, the highest potential enzyme‐catalyzed rates of respiratory enzymes for R are predicted to occur at 67.0 ± 1.2°C and the maximum temperature sensitivity at 41.4 ± 0.7°C from MMRT. The average curvature (average negative Δ C P ‡) was −1.2 ± 0.1 kJ mol−1 K−1. Interestingly, Topt, Tinf and Δ C P ‡ appear insignificantly different across biomes and plant functional types, suggesting that thermal response of respiratory enzymes in leaves could be conserved. The derived parameters from MMRT can serve as thermal traits for plant leaves that represent the collective temperature response of metabolic respiratory enzymes and could be useful to understand regulations of R under a warmer climate. MMRT extends the classic TST to enzyme‐catalyzed reactions and provides an accurate and mechanistic model for the short‐term temperature response of R around the globe. [ABSTRACT FROM AUTHOR]

Abstract: Large spatial and temporal gradients in rainfall and temperature occur across Australia. This heterogeneity drives ecological differentiation in vegetation structure and ecophysiology. We examined multiple leaf‐scale traits, including foliar 13C isotope discrimination (Δ13C), rates of photosynthesis and foliar N concentration and their relationships with multiple climate variables. Fifty‐five species across 27 families were examined across eight sites spanning contrasting biomes. Key questions addressed include: (i) Does Δ13C and intrinsic water‐use efficiency (WUEi) vary with climate at a continental scale? (ii) What are the seasonal and spatial patterns in Δ13C/WUEi across biomes and species? (iii) To what extent does Δ13C reflect variation in leaf structural, functional and nutrient traits across climate gradients? and (iv) Does the relative importance of assimilation and stomatal conductance in driving variation in Δ13C differ across seasons? We found that MAP, temperature seasonality, isothermality and annual temperature range exerted independent effects on foliar Δ13C/WUEi. Temperature‐related variables exerted larger effects than rainfall‐related variables. The relative importance of photosynthesis and stomatal conductance (gs) in determining Δ13C differed across seasons: Δ13C was more strongly regulated by gs during the dry‐season and by photosynthetic capacity during the wet‐season. Δ13C was most strongly correlated, inversely, with leaf mass area ratio among all leaf attributes considered. Leaf Nmass was significantly and positively correlated with MAP during dry‐ and wet‐seasons and with moisture index (MI) during the wet‐season but was not correlated with Δ13C. Leaf Pmass showed significant positive relationship with MAP and Δ13C only during the dry‐season. For all leaf nutrient‐related traits, the relationships obtained for Δ13C with MAP or MI indicated that Δ13C at the species level reliably reflects the water status at the site level. Temperature and water availability, not foliar nutrient content, are the principal factors influencing Δ13C across Australia. [ABSTRACT FROM AUTHOR]

Contents986I.987II.987III.988IV.991V.992VI.995VII.997VIII.998References998 Summary: It has been 75 yr since leaf respiratory metabolism in the light (day respiration) was identified as a low‐flux metabolic pathway that accompanies photosynthesis. In principle, it provides carbon backbones for nitrogen assimilation and evolves CO2 and thus impacts on plant carbon and nitrogen balances. However, for a long time, uncertainties have remained as to whether techniques used to measure day respiratory efflux were valid and whether day respiration responded to environmental gaseous conditions. In the past few years, significant advances have been made using carbon isotopes, ‘omics’ analyses and surveys of respiration rates in mesocosms or ecosystems. There is substantial evidence that day respiration should be viewed as a highly dynamic metabolic pathway that interacts with photosynthesis and photorespiration and responds to atmospheric CO2 mole fraction. The view of leaf day respiration as a constant and/or negligible parameter of net carbon exchange is now outdated and it should now be regarded as a central actor of plant carbon‐use efficiency. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) have key roles in leaf metabolism, resulting in a strong coupling of chemical composition traits to metabolic rates in field-based studies. However, in such studies, it is difficult to disentangle the effects of nutrient supply per se on trait-trait relationships., Our study assessed how high and low N (5 mM and 0.4 mM, respectively) and P (1 mM and 2 μM, respectively) supply in 37 species from six plant functional types (PTFs) affected photosynthesis ( A) and respiration ( R) (in darkness and light) in a controlled environment., Low P supply increased scaling exponents (slopes) of area-based log-log A-N or R-N relationships when N supply was not limiting, whereas there was no P effect under low N supply. By contrast, scaling exponents of A-P and R-P relationships were altered by P and N supply. Neither R : A nor light inhibition of leaf R was affected by nutrient supply. Light inhibition was 26% across nutrient treatments; herbaceous species exhibited a lower degree of light inhibition than woody species., Because N and P supply modulates leaf trait−trait relationships, the next generation of terrestrial biosphere models may need to consider how limitations in N and P availability affect trait−trait relationships when predicting carbon exchange. [ABSTRACT FROM AUTHOR]

Understanding of the extent of acclimation of light-saturated net photosynthesis ( An) to temperature ( T), and associated underlying mechanisms, remains limited. This is a key knowledge gap given the importance of thermal acclimation for plant functioning, both under current and future higher temperatures, limiting the accuracy and realism of Earth system model ( ESM) predictions. Given this, we analysed and modelled T-dependent changes in photosynthetic capacity in 10 wet-forest tree species: six from temperate forests and four from tropical forests. Temperate and tropical species were each acclimated to three daytime growth temperatures ( Tgrowth): temperate - 15, 20 and 25 °C; tropical - 25, 30 and 35 °C. CO2 response curves of An were used to model maximal rates of Ru BP (ribulose-1,5-bisphosphate) carboxylation ( Vcmax) and electron transport ( Jmax) at each treatment's respective Tgrowth and at a common measurement T (25 °C). SDS- PAGE gels were used to determine abundance of the CO2-fixing enzyme, Rubisco. Leaf chlorophyll, nitrogen (N) and mass per unit leaf area ( LMA) were also determined. For all species and Tgrowth, An at current atmospheric CO2 partial pressure was Rubisco-limited. Across all species, LMA decreased with increasing Tgrowth. Similarly, area-based rates of Vcmax at a measurement T of 25 °C ( Vcmax25) linearly declined with increasing Tgrowth, linked to a concomitant decline in total leaf protein per unit leaf area and Rubisco as a percentage of leaf N. The decline in Rubisco constrained Vcmax and An for leaves developed at higher Tgrowth and resulted in poor predictions of photosynthesis by currently widely used models that do not account for Tgrowth-mediated changes in Rubisco abundance that underpin the thermal acclimation response of photosynthesis in wet-forest tree species. A new model is proposed that accounts for the effect of Tgrowth-mediated declines in Vcmax25 on An, complementing current photosynthetic thermal acclimation models that do not account for T sensitivity of Vcmax25. [ABSTRACT FROM AUTHOR]

One of the major challenges in ecology is to understand how ecosystems respond to changes in environmental conditions, and how taxonomic and functional diversity mediate these changes. In this study, we use a trait-spectra and individual-based model, to analyse variation in forest primary productivity along a 3.3 km elevation gradient in the Amazon-Andes. The model accurately predicted the magnitude and trends in forest productivity with elevation, with solar radiation and plant functional traits (leaf dry mass per area, leaf nitrogen and phosphorus concentration, and wood density) collectively accounting for productivity variation. Remarkably, explicit representation of temperature variation with elevation was not required to achieve accurate predictions of forest productivity, as trait variation driven by species turnover appears to capture the effect of temperature. Our semi-mechanistic model suggests that spatial variation in traits can potentially be used to estimate spatial variation in productivity at the landscape scale. [ABSTRACT FROM AUTHOR]

Leaf dark respiration ( Rdark) represents an important component controlling the carbon balance in tropical forests. Here, we test how nitrogen (N) and phosphorus (P) affect Rdark and its relationship with photosynthesis using three widely separated tropical forests which differ in soil fertility., Rdark was measured on 431 rainforest canopy trees, from 182 species, in French Guiana, Peru and Australia. The variation in Rdark was examined in relation to leaf N and P content, leaf structure and maximum photosynthetic rates at ambient and saturating atmospheric CO2 concentration., We found that the site with the lowest fertility (French Guiana) exhibited greater rates of Rdark per unit leaf N, P and photosynthesis. The data from Australia, for which there were no phylogenetic overlaps with the samples from the South American sites, yielded the most distinct relationships of Rdark with the measured leaf traits., Our data indicate that no single universal scaling relationship accounts for variation in Rdark across this large biogeographical space. Variability between sites in the absolute rates of Rdark and the Rdark : photosynthesis ratio were driven by variations in N- and P-use efficiency, which were related to both taxonomic and environmental variability. [ABSTRACT FROM AUTHOR]

The article discusses 18th phytologist workshop "The Kok effect: beyond the artefact, emerging leaf mechanisms (KOALA)" held at Angers, France, on July, 2016, on change in quantum yield of net photosynthesis. Topics include photosynthetic organs of plants accompanied by concurrent efflux of carbon dioxide by photorespiration and day respiration; difference between inlet and outlet air in open gas exchange systems; and leaf respiration in the light for ecosystem.

Combining hydraulic- and carbon-related measurements helps to understand drought-induced plant mortality. Here, we investigated the role that plant respiration ( R) plays in determining carbon budgets under drought., We measured the hydraulic conductivity of stems and roots, and gas exchange and nonstructural carbohydrate ( NSC) concentrations of leaves, stems and roots of seedlings of two resprouting species exposed to drought or well-watered conditions: Ulmus minor (riparian tree) and Quercus ilex (dryland tree)., With increasing water stress (occurring more rapidly in larger U. minor), declines in leaf, stem and root R were less pronounced than that in leaf net photosynthetic CO2 uptake ( Pn). Daytime whole-plant carbon gain was negative below −4 and −6 MPa midday xylem water potential in U. minor and Q. ilex, respectively. Relative to controls, seedlings exhibiting shoot dieback suffered c. 80% loss of hydraulic conductivity in both species, and reductions in NSC concentrations in U. minor. Higher drought-induced depletion of NSC reserves in U. minor was related to higher plant R, faster stomatal closure, and premature leaf-shedding., Differences in drought resistance relied on the ability to maintain hydraulic conductivity during drought, rather than tolerating conductivity loss. Root hydraulic failure elicited shoot dieback and precluded resprouting without root NSC reserves being apparently limiting for R. [ABSTRACT FROM AUTHOR]

High-temperature tolerance in plants is important in a warming world, with extreme heat waves predicted to increase in frequency and duration, potentially leading to lethal heating of leaves. Global patterns of high-temperature tolerance are documented in animals, but generally not in plants, limiting our ability to assess risks associated with climate warming. To assess whether there are global patterns in high-temperature tolerance of leaf metabolism, we quantified Tcrit (high temperature where minimal chlorophyll a fluorescence rises rapidly and thus photosystem II is disrupted) and Tmax (temperature where leaf respiration in darkness is maximal, beyond which respiratory function rapidly declines) in upper canopy leaves of 218 plant species spanning seven biomes. Mean site-based Tcrit values ranged from 41.5 °C in the Alaskan arctic to 50.8 °C in lowland tropical rainforests of Peruvian Amazon. For Tmax, the equivalent values were 51.0 and 60.6 °C in the Arctic and Amazon, respectively. Tcrit and Tmax followed similar biogeographic patterns, increasing linearly ( ˜8 °C) from polar to equatorial regions. Such increases in high-temperature tolerance are much less than expected based on the 20 °C span in high-temperature extremes across the globe. Moreover, with only modest high-temperature tolerance despite high summer temperature extremes, species in mid-latitude (~20-50°) regions have the narrowest thermal safety margins in upper canopy leaves; these regions are at the greatest risk of damage due to extreme heat-wave events, especially under conditions when leaf temperatures are further elevated by a lack of transpirational cooling. Using predicted heat-wave events for 2050 and accounting for possible thermal acclimation of Tcrit and Tmax, we also found that these safety margins could shrink in a warmer world, as rising temperatures are likely to exceed thermal tolerance limits. Thus, increasing numbers of species in many biomes may be at risk as heat-wave events become more severe with climate change. [ABSTRACT FROM AUTHOR]

Simulations of photosynthesis by terrestrial biosphere models typically need a specification of the maximum carboxylation rate ( Vcmax). Estimating this parameter using A- Ci curves (net photosynthesis, A, vs intercellular CO2 concentration, Ci) is laborious, which limits availability of Vcmax data. However, many multispecies field datasets include net photosynthetic rate at saturating irradiance and at ambient atmospheric CO2 concentration ( Asat) measurements, from which Vcmax can be extracted using a 'one-point method'., We used a global dataset of A- Ci curves (564 species from 46 field sites, covering a range of plant functional types) to test the validity of an alternative approach to estimate Vcmax from Asat via this 'one-point method'., If leaf respiration during the day ( Rday) is known exactly, Vcmax can be estimated with an r2 value of 0.98 and a root-mean-squared error ( RMSE) of 8.19 μmol m−2 s−1. However, Rday typically must be estimated. Estimating Rday as 1.5% of Vcmax, we found that Vcmax could be estimated with an r2 of 0.95 and an RMSE of 17.1 μmol m−2 s−1., The one-point method provides a robust means to expand current databases of field-measured Vcmax, giving new potential to improve vegetation models and quantify the environmental drivers of Vcmax variation. [ABSTRACT FROM AUTHOR]

In intact leaves, mitochondrial populations are highly heterogeneous among contrasting cell types; how such contrasting populations respond to sustained changes in the environment remains, however, unclear. Here, we examined respiratory rates, mitochondrial protein composition and response to growth temperature in photosynthetic (mesophyll) and non-photosynthetic (epidermal) cells from fully expanded leaves of warm-developed ( WD) and cold-developed ( CD) broad bean ( V icia faba L.). Rates of respiration were significantly higher in mesophyll cell protoplasts ( MCPs) than epidermal cell protoplasts ( ECPs), with both protoplast types exhibiting capacity for cytochrome and alternative oxidase activity. Compared with ECPs, MCPs contained greater relative quantities of porin, suggesting higher mitochondrial surface area in mesophyll cells. Nevertheless, the relative quantities of respiratory proteins (normalized to porin) were similar in MCPs and ECPs, suggesting that ECPs have lower numbers of mitochondria yet similar protein complement to MCP mitochondria (albeit with lower abundance serine hydroxymethyltransferase). Several mitochondrial proteins (both non-photorespiratory and photorespiratory) exhibited an increased abundance in response to cold in both protoplast types. Based on estimates of individual protoplast respiration rates, combined with leaf cell abundance data, epidermal cells make a small but significant (2%) contribution to overall leaf respiration which increases twofold in the cold. Taken together, our data highlight the heterogeneous nature of mitochondrial populations in leaves, both among contrasting cell types and in how those populations respond to growth temperature. [ABSTRACT FROM AUTHOR]

Recent compilations of experimental and observational data have documented global temperature-dependent patterns of variation in leaf dark respiration ( R), but it remains unclear whether local adjustments in respiration over time (through thermal acclimation) are consistent with the patterns in R found across geographical temperature gradients., We integrated results from two global empirical syntheses into a simple temperature-dependent respiration framework to compare the measured effects of respiration acclimation-over-time and variation-across-space to one another, and to a null model in which acclimation is ignored. Using these models, we projected the influence of thermal acclimation on: seasonal variation in R; spatial variation in mean annual R across a global temperature gradient; and future increases in R under climate change., The measured strength of acclimation-over-time produces differences in annual R across spatial temperature gradients that agree well with global variation-across-space. Our models further project that acclimation effects could potentially halve increases in R (compared with the null model) as the climate warms over the 21st Century., Convergence in global temperature-dependent patterns of R indicates that physiological adjustments arising from thermal acclimation are capable of explaining observed variation in leaf respiration at ambient growth temperatures across the globe. [ABSTRACT FROM AUTHOR]

To determine (1) whether acclimation of carbon metabolism to low temperatures results in recovery of the relative growth rate ( RGR) of plants in the cold and (2) the source of N underpinning cold acclimation in A rabidopsis thaliana, we supplied plants with a nutrient solution labelled with 15N and subjected them to a temperature shift (from 23 to 5 ° C). Whole-plant RGR of cold-treated plants was initially less than 30% of that of warm-maintained control plants. After 14 d, new leaves with a cold-acclimated phenotype emerged, with the RGR of cold-treated plants increasing by 50%; there was an associated recovery of root RGR and doubling of the net assimilation rate ( NAR). The development of new tissues in the cold was supported initially by re-allocation of internal sources of N. In the longer term, the majority (80%) of N in the new leaves was derived from the external solution. Hence, both the nutrient status of the plant and the current availability of N from external sources are important in determining recovery of growth at low temperature. Collectively, our results reveal that both increased N use efficiency and increases in nitrogen content per se play a role in the recovery of carbon metabolism in the cold. [ABSTRACT FROM AUTHOR]

Leaf dark respiration ( Rdark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits., Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in Rdark., Area-based Rdark at the prevailing average daily growth temperature ( T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8-28°C). By contrast, Rdark at a standard T (25°C, Rdark25) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher Rdark25 at a given photosynthetic capacity ( Vcmax25) or leaf nitrogen concentration ([N]) than species at warmer sites. Rdark25 values at any given Vcmax25 or [N] were higher in herbs than in woody plants., The results highlight variation in Rdark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of Rdark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs). [ABSTRACT FROM AUTHOR]

Despite concern about the status of carbon (C) in the Arctic tundra, there is currently little information on how plant respiration varies in response to environmental change in this region. We quantified the impact of long-term nitrogen (N) and phosphorus (P) treatments and greenhouse warming on the short-term temperature ( T) response and sensitivity of leaf respiration ( R), the high- T threshold of R, and associated traits in shoots of the Arctic shrub Betula nana in experimental plots at Toolik Lake, Alaska. Respiration only acclimated to greenhouse warming in plots provided with both N and P (resulting in a ~30% reduction in carbon efflux in shoots measured at 10 and 20 °C), suggesting a nutrient dependence of metabolic adjustment. Neither greenhouse nor N+P treatments impacted on the respiratory sensitivity to T ( Q10); overall, Q10 values decreased with increasing measuring T, from ~3.0 at 5 °C to ~1.5 at 35 °C. New high-resolution measurements of R across a range of measuring Ts (25-70 °C) yielded insights into the T at which maximal rates of R occurred ( Tmax). Although growth temperature did not affect Tmax, N+P fertilization increased Tmax values ~5 °C, from 53 to 58 °C. N+P fertilized shoots exhibited greater rates of R than nonfertilized shoots, with this effect diminishing under greenhouse warming. Collectively, our results highlight the nutrient dependence of thermal acclimation of leaf R in B. nana, suggesting that the metabolic efficiency allowed via thermal acclimation may be impaired at current levels of soil nutrient availability. This finding has important implications for predicting carbon fluxes in Arctic ecosystems, particularly if soil N and P become more abundant in the future as the tundra warms. [ABSTRACT FROM AUTHOR]

Information on several topics discussed at the Eight New Phytologist Workshop in Canberra, Australian Capital Territory and Kioloa, New South Wales in July 2013 is presented. Topics include plant respiration (R), model variations in leaf respiration, and temperature response of leaf R. The meeting featured several participants including Richard Norby, Lasantha Weerasinghe, and Jeff Dukes.

We tested whether snow gum ( Eucalyptus pauciflora) trees growing in thermally contrasting environments exhibit generalizable temperature ( T) response functions of leaf respiration ( R) and fluorescence ( Fo). Measurements were made on pot-grown saplings and field-grown trees (growing between 1380 and 2110 m a.s.l.). Using a continuous, high-resolution protocol, we quantified T response curves of R and Fo - these data were used to identify an algorithm for modelling R- T curves at subcritical T's and establish variations in heat tolerance. For the latter, we quantified Tmax [ T where R is maximal] and Tcrit [ T where Fo rises rapidly]. Tmax ranged from 51 to 57 ° C, varying with season (e.g. winter > summer). Tcrit ranged from 41 to 49 ° C in summer and from 58 to 63 ° C in winter. Thus, surprisingly, leaf energy metabolism was more heat-tolerant in trees experiencing ice-encasement in winter than warmer conditions in summer. A polynomial model fitted to log-transformed R data provided the best description of the T-sensitivity of R (between 10 and 45 ° C); using these model fits, we found that the negative slope of the Q10- T relationship was greater in winter than in summer. Collectively, our results (1) highlight high- T limits of energy metabolism in E. pauciflora and (2) provide a framework for improving representation of T-responses of leaf R in predictive models. [ABSTRACT FROM AUTHOR]

Laboratory studies indicate that plant respiratory efficiency may decrease in response to low nutrient availability due to increased partitioning of electrons to the energy-wasteful alternative oxidase ( AOX); however, field confirmation of this hypothesis is lacking. We therefore investigated plant respiratory changes associated with succession and retrogression in soils aged from 10 to 120 000 years along the Franz Josef soil chronosequence, New Zealand. Respiration rates and electron partitioning were determined based on oxygen isotopic fractionation. Leaf structural traits, foliar nutrient status, carbohydrates and species composition were measured as explanatory variables. Although soil nutrient levels and species composition varied by site along the chronosequence, foliar respiration across all sites and species corresponded strongly with leaf nitrogen concentration ( r2 = 0.8). In contrast, electron partitioning declined with increasing nitrogen/phosphorus ( r2 = 0.23) and AOX activity correlated with phosphorus ( r2 = 0.64). Independently, total respiration was further associated with foliar Cu, possibly linked to its effect on AOX. Independent control of AOX and cytochrome pathway activities is also discussed. These responses of plant terminal respiratory oxidases - and therefore respiratory carbon efficiency - to multiple nutrient deficiencies demonstrate that modulation of respiratory metabolism may play an important role in plant responses to nutrient gradients. [ABSTRACT FROM AUTHOR]

We investigated whether plants adapted to thermally contrasting environments (e.g. tropical-temperate habitats) exhibit inherent differences in leaf trait scaling relationships., Thirteen tropical and 12 temperate species (all characteristic of wet forests) were grown in a glasshouse (25/20 °C day/night). A range of leaf traits were quantified, including mass-based leaf nitrogen [N], mass per unit area ( LMA), light-saturated photosynthesis ( A) and respiration ( Rdark)., Average area- and mass-based rates of net CO2 exchange were higher in the temperate species, compared to their tropical counterparts. Average leaf [N] and LMA values were also higher in temperate species than in their tropical counterparts., The higher LMA in the metabolically more active temperate species was the most striking contrast to the patterns and predictions of the GLOPNET leaf trait data base, and was associated with different elevations (i.e. y-axis intercepts) but not slopes of bivariate trait scaling relationships. As expected, mass-based rates of A and Rdark scaled positively with increasing [N] and negatively with increasing LMA in both tropical and temperate species. No differences were found between temperate and tropical species groups in terms of log-log scaling relationships linking A and Rdark to N. However, at any given LMA, mass-based values of [N], A and Rdark were all higher in the temperate species than in their tropical counterparts., Underpinning higher A in temperate species was a higher capacity for carboxylation ( Vcmax) and Ru BP regeneration ( Jmax), with Jmax: Vcmax being greater in temperate species., In conclusion, our results suggest that as a consequence of greater overall N investment as well as greater proportional N investment in metabolic capacity, cool-adapted temperate wet forest species exhibit higher photosynthetic and respiration rates than their warm-adapted tropical counterparts when compared in a common environment. [ABSTRACT FROM AUTHOR]