CO Labeling Research Articles

Rhizosphere priming promotes plant nitrogen acquisition by microbial necromass recycling.

Nitrogen availability in the rhizosphere relies on root-microorganism interactions, where root exudates trigger soil organic matter (SOM) decomposition through the rhizosphere priming effect (RPE). Though microbial necromass contribute significantly to organically bound soil nitrogen (N), the role of RPEs in regulating necromass recycling and plant nitrogen acquisition has received limited attention. We used 15N natural abundance as a proxy for necromass-N since necromass is enriched in 15N compared to other soil-N forms. We combined studies using the same experimental design for continuous 13CO2 labelling of various plant species and the same soil type, but considering top- and subsoil. RPE were quantified as difference in SOM-decomposition between planted and unplanted soils. Results showed higher plant N uptake as RPEs increased. The positive relationship between 15N-enrichment of shoots and roots and RPEs indicated an enhanced necromass-N turnover by RPE. Moreover, our data revealed that RPEs were saturated with increasing carbon (C) input via rhizodeposition in topsoil. In subsoil, RPEs increased linearly within a small range of C input indicating a strong effect of root-released C on decomposition rates in deeper soil horizons. Overall, this study confirmed the functional importance of rhizosphere C input for plant N acquisition through enhanced necromass turnover by RPEs.

Increasing the uptake of plant-based diets: An analysis of the impact of a CO2 food label

Reducing the environmental footprint of the global food system significantly depends on shifting to more plant-based diets. However, deep-rooted eating habits and a general lack of awareness about food-related emissions hinder large-scale dietary shifts. Demand-side food policies can accelerate this transition towards plant-based diets. One policy instrument that may increase awareness of diet-related emissions and facilitate climate-friendly food consumption choices is a CO2 food label. The success of such demand-side food policies depends on socio-political and market acceptance. However, there is a lack of empirical evidence regarding the socio-political (i.e., feasibility) and market acceptance (i.e., effectiveness at changing behavioral intentions) of CO2 food labels. We also require more knowledge about the potential spillover effects of CO2 food labels on support for more ambitious demand-side food policies. The paper presents evidence from a survey experiment with a sample of Swiss residents (N = 2372) who were randomly provided with information about an established CO2 food label. The survey experiment was embedded in a cooperation throughout a larger long-term project with the second-largest Swiss retailer, which launched one of the world's first CO2 food labels in 2021. Findings show that providing information on a CO2 food label strengthens individuals' behavioral change intentions and support for a mandatory governmental CO2 food label. However, no spillover effect on support for other food policy instruments is identified, which also means that the study finds no crowding out effect by voluntary CO2 labelling initiatives on the support of governmental food policy measures. The results imply that a CO2 food label enjoys high market and socio-political acceptance.

13 CO2 labelling as a tool for elucidating the mechanism of cuticle development: a case of Clusia rosea.

The plant cuticle is an important plant-atmosphere boundary, the synthesis and maintenance of which represents a significant metabolic cost. Only limited information regarding cuticle dynamics is available. We determined the composition and dynamics of Clusia rosea cuticular waxes and matrix using 13 CO2 labelling, compound-specific and bulk isotope ratio mass spectrometry. Collodion was used for wax collection; gas exchange techniques to test for any collodion effects on living leaves. Cutin matrix (MX) area density did not vary between young and mature leaves and between leaf sides. Only young leaves incorporated new carbon into their MX. Collodion-based sampling discriminated between epicuticular (EW) and intracuticular wax (IW) effectively. Epicuticular differed in composition from IW. The newly synthetised wax was deposited in IW first and later in EW. Both young and mature leaves synthetised IW and EW. The faster dynamics in young leaves were due to lower wax coverage, not a faster synthesis rate. Longer-chain alkanes were deposited preferentially on the abaxial, stomatous leaf side, producing differences between leaf sides in wax composition. We introduce a new, sensitive isotope labelling method and demonstrate that cuticular wax is renewed during leaf ontogeny of C. rosea. We discuss the ecophysiological significance of the new insights.

Deep learning for characterizing CO2 migration in time-lapse seismic images

Time-lapse (or 4-D) seismic data play an important role in monitoring the spatial CO2 distribution during and after the injection period. However, traditional interpretation or prediction of CO2 distribution is time-consuming and might be sensitive to the quality of 4D seismic data. To solve these problems, we propose a deep-learning-based method to efficiently and accurately characterize CO2 plumes in time-lapse seismic data. We first introduce a workflow to build 3-D realistic impedance models containing CO2 plumes with various shapes, sizes, and locations. From the impedance models, we then simulate synthetic seismic datasets and automatically obtain the corresponding CO2 label volumes. We extract real noise from field seismic datasets and add the noise to the synthetic ones to make them more realistic. We further construct a diverse and realistic training dataset with the combination of synthetic data containing CO2 plumes and real data without CO2 plumes that are randomly cropped from field seismic data before CO2 injection. We finally utilize the training datasets without any human labeling to train a 3-D deep U-shape convolutional neural network for detecting CO2 plumes in the Sleipner time-lapse seismic images. Compared to traditional interpretation methods that take several days or even weeks, our method takes only 29 s using one graphics processing unit (GPU) to predict CO2 plumes in a 512*512*256 seismic volume. Besides, our CO2 prediction can achieve 95.8% accuracy (compared to the manual interpretation) and could distinguish reflections of CO2 plumes from the ones of pre-existing fluids, thin layers, and noise. To more accurately characterize the CO2 plumes migration, we use dynamic image warping to compute relative shifts that register the time-lapse seismic volumes before and after CO2 injection and then apply the same shifts to the predicted CO2 plumes. By doing this, we are able to reduce the inconsistencies that may be introduced by acquisition, processing, push-down effect (velocity decrease by injected CO2), and pull-up effect (wavelet distortion), which is helpful to more accurately characterize the CO2 plumes migration.

Deep learning multiphysics network for imaging CO2 saturation and estimating uncertainty in geological carbon storage

AbstractMultiphysics inversion exploits different types of geophysical data that often complement each other and aims to improve overall imaging resolution and reduce uncertainties in geophysical interpretation. Despite the advantages, traditional multiphysics inversion is challenging because it requires a large amount of computational time and intensive human interactions for preprocessing data and finding trade‐off parameters. These issues make it nearly impossible for traditional multiphysics inversion to be applied as a real‐time monitoring tool for geological carbon storage. In this paper, we present a deep learning (DL) multiphysics network for imaging CO2 saturation in real time. The multiphysics network consists of three encoders for analysing seismic, electromagnetic and gravity data and shares one decoder for combining imaging capabilities of the different geophysical data for better predicting CO2 saturation. The network is trained on pairs of CO2 label models and multiphysics data so that it can directly image CO2 saturation. We use the bootstrap aggregating method to enhance the imaging accuracy and estimate uncertainties associated with CO2 saturation images. Using realistic CO2 label models and multiphysics data derived from the Kimberlina CO2 storage model, we evaluate the performance of the deep learning multiphysics network and compare its imaging results to those from the deep learning single‐physics networks. Our modelling experiments show that the deep learning multiphysics network for seismic, electromagnetic, and gravity data not only improves the imaging accuracy but also reduces uncertainties associated with CO2 saturation images. Our results also suggest that the deep learning multiphysics network for the non‐seismic data (i.e., electromagnetic and gravity) can be used as an effective low‐cost monitoring tool in between regular seismic monitoring.

Imperfect emissions information during flight choices and the role of CO2 labelling

Although the airline sector contributes to just 3% of the world's CO2 emissions, air travel is a highly CO2-intensive activity. Unlike other energy-related household decisions, there is little standardised, comparable, regulated information available to consumers regarding the environmental impacts of different airlines. Imperfect information in this market therefore appears very likely. This paper presents the results of a discrete choice experiment which uses a nationally representative sample of 209 participants in Ireland to explore how point-of-sale flight emission labelling influences choice. There are two keys findings: first, a comparative CO2 label, similar to existing EU colour-coded labels (appliances, for example), leads to a shift to lower emission flight choices, even when they cost more; second, the effect is very large: on average, households are willing to pay €77 more for each tonne of CO2 reduced. Unlike other household energy efficiency decisions (appliances, cars and buildings, for example), choosing more energy efficient flights has no private monetary return in the form of lower future energy bills. It therefore represents a purer test of willingness to pay for a public good (a low CO2 environment). Results provide evidence to support policy recommendations of emission labelling in the short-run and environmental education in the long-run.

Negative effects of low root temperatures on water and carbon relations in temperate tree seedlings assessed by dual isotopic labelling.

Low root zone temperatures restrict water and carbon (C) uptake and transport in plants and may contribute to the low temperature limits of tree growth. Here, we quantified the effects of low root temperatures on xylem conductance, photosynthetic C assimilation and phloem C transport in seedlings of four temperate tree species (two broad-leaved and two conifer species) by applying a simultaneous stable isotope labelling of 2H-enriched source water and 13C-enriched atmospheric CO2. Six days before the pulse labelling, the seedlings were transferred to hydroponic tubes and exposed to three different root temperatures (2, 7 and 15 °C), while all seedlings received the same, warm air temperatures (between 18 and 24 °C). Root cooling led to drought-like symptoms with reduced growth, leaf water potentials and stomatal conductance, indicating increasingly adverse conditions for water uptake and transport with decreasing root temperatures. Averaged across all four species, water transport to leaves was reduced by 40% at 7 °C and by 70% at 2 °C root temperature relative to the 15 °C treatment, while photosynthesis was reduced by 20 and 40% at 7 and 2 °C, respectively. The most severe effects were found on the phloem C transport to roots, which was reduced by 60% at 7 °C and almost ceased at 2 °C in comparison with the 15 °C root temperature treatment. This extreme effect on C transport was likely due to a combination of simultaneous reductions of phloem loading, phloem mass flow and root growth. Overall, the dual stable isotope labelling proved to be a useful method to quantify water and C relations in cold-stressed trees and highlighted the potentially important role of hydraulic constraints induced by low soil temperatures as a contributing factor for the climatic distribution limits of temperate tree species.

Dark CO2 fixation in temperate beech and pine forest soils

Soils are the largest terrestrial organic carbon pool and the largest terrestrial source of atmospheric CO2. Non-phototrophic CO2 fixation by microbes re-fixes and recycles CO2 respired in soils. Our previous study showed that in temperate deciduous forest soil profiles, rates of dark CO2 fixation were proportional to microbial biomass, irrespective of soil depth. However, the amount and quality of organic matter entering different soil depths vary for different temperate forest types and these influence microbial communities with unknown consequences for CO2 fixation rates. To test whether differences in the amount and quality of SOC caused by tree species affect dark CO2 fixation rates with depth, we conducted a study using acidic soils from two forest plots from the Schorfheide-Chorin Exploratory, Germany. These soils, dominated by either beech (deciduous) or pine (coniferous) tree stands differ in their SOC content and quality. We traced the incorporation of 2% (v:v) 13C–CO2 label into microbial biomass and estimated the CO2 fixation rates relative to microbial biomass carbon content (in μg C g MBC−1 d−1) across the soil profiles. The rates of dark CO2 fixation per g MBC were similar across the beech soil profiles, but significantly lower in the pine soils at the B2 and BC horizons, suggesting that while dark CO2 fixation rates are linked to MBC in deciduous forest soils, other factors influence dark CO2 fixation rates in coniferous forest soils. The pine subsoils had low SOC content and quality, with a microbial community enriched with heterotrophic fermenters like Chloroflexi that are predicted to have a lower potential for heterotrophic CO2 fixation compared to the other dominant bacteria phyla. In contrast, the beech soil profiles, characterized by higher SOC inputs, featured higher fractions of copiotrophs like Proteobacteria, Acidobacteria, and Actinobacteria predicted to have high heterotrophic CO2 fixation potential. We thus speculate that in contrast to the beech soils, lower SOC inputs in the pine subsoils affected the community composition, leading to lower CO2 fixation rates. We further made comparisons to soils dominated by mixed deciduous trees and featuring a higher MBC and SOC content. Over this range of temperate forest soils, CO2 fixation rates were highest in the mixed deciduous forest soils, with MBC and Shannon index (used as a proxy parameter for community composition) showing the strongest correlations with the varying CO2 fixation rates. Our study suggests that predictions of dark CO2 fixation rates need to consider tree-species specific or site-specific conditions, as these may alter root carbon inputs and affect microbial community composition and their metabolic CO2 fixation potentials in soil.

Assessing Protein Synthesis and Degradation Rates in Arabidopsis thaliana Using Amino Acid Analysis.

Plants continually synthesize and degrade proteins, for example, to adjust protein content during development or during adaptation to new environments. In order to estimate global protein synthesis and degradation rates in plants, we developed a relatively simple and inexpensive method using a combination of 13 CO2 labeling and mass spectrometry-based analyses. Arabidopsis thaliana plants are subjected to a 24-hr 13 CO2 pulse followed by a 4-day 12 CO2 chase. Soluble alanine and serine from total protein and glucose from cell wall material are analyzed by gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) and their 13 C enrichment (%) is estimated. The rate of protein synthesis during the 13 CO2 pulse experiment is defined as the rate of incorporation of labeled amino acids into proteins normalized by a correction factor for incomplete enrichment in free amino acid pools. The rate of protein degradation is estimated as the difference between the rate of protein synthesis and the relative growth rate calculated using the 13 C enrichment of glucose from cell wall material. Degradation rates are also estimated from the 12 CO2 pulse experiment. The following method description includes setting up and performing labeling experiments, preparation and measurement of samples, and calculation steps. In addition, an R script is provided for the calculations. 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Setting up the 13 CO2 labeling system and stable isotope labeling of Arabidopsis thaliana rosette leaves Basic Protocol 2: Extraction of soluble amino acids for GC-TOF-MS analysis Basic Protocol 3: Preparation of amino acids from total protein for GC-TOF-MS analysis Basic Protocol 4: Preparation of sugars from cell wall material for GC-TOF-MS analysis Basis Protocol 5: GC-TOF-MS analysis of 13 C-labeled samples and estimation of 13 C enrichment (%) Basis Protocol 6: Estimation of protein synthesis and degradation rates.

Moss stomata do not respond to light and CO2 concentration but facilitate carbon uptake by sporophytes: a gas exchange, stomatal aperture, and 13 C-labelling study.

Stomata exert control on fluxes of CO2 and water (H2 O) in the majority of vascular plants and thus are pivotal for planetary fluxes of carbon and H2 O. However, in mosses, the significance and possible function of the sporophytic stomata are not well understood, hindering understanding of the ancestral function and evolution of these key structures of land plants. Infrared gas analysis and 13 CO2 labelling, with supporting data from gravimetry and optical and scanning electron microscopy, were used to measure CO2 assimilation and water exchange on young, green, ± fully expanded capsules of 11 moss species with a range of stomatal numbers, distributions, and aperture sizes. Moss sporophytes are effectively homoiohydric. In line with their open fixed apertures, moss stomata, contrary to those in tracheophytes, do not respond to light and CO2 concentration. Whereas the sporophyte cuticle is highly impermeable to gases, stomata are the predominant sites of 13 CO2 entry and H2 O loss in moss sporophytes, and CO2 assimilation is closely linked to total stomatal surface areas. Higher photosynthetic autonomy of moss sporophytes, consequent on the presence of numerous stomata, may have been the key to our understanding of evolution of large, gametophyte-independent sporophytes at the onset of plant terrestrialization.

Rhizosphere priming effects of Lolium perenne and Trifolium repens depend on phosphorus fertilization and biological nitrogen fixation

Live roots can stimulate microbial soil organic matter (SOM) decomposition and nutrient cycling, which is termed as the rhizosphere priming effect (RPE). Compared to nitrogen (N) availability, fewer studies have focused on the effect of phosphorus (P) availability on the RPE. Here we investigated the RPEs of ryegrass (Lolium perenne) and clover (Trifolium repens) with and without P fertilization (4 g P m−2) at three sampling times (Day 30, Day 44, and Day 58 after planting). A continuous 13C–CO2 labeling method was used to separate soil-derived CO2 from root-derived CO2. A nutrient budget method was applied to evaluate the rhizosphere effect on net soil N and P release for plant uptake. We found that ryegrass and clover induced positive RPEs in most plant-soil combinations, ranging from −1% to 134%. Ryegrass exhibited a larger RPE than clover by Day 30, but clover exhibited a larger RPE than ryegrass by Day 44 and Day 58, possibly due to larger shoot biomass regrowth rates, root activity, and rhizodeposition during the later stages. P fertilization significantly decreased the RPE of ryegrass by Day 44 and Day 58, but did not change the RPE of ryegrass by Day 30 and clover at all three sampling times. The reduced RPE of ryegrass with P fertilization was associated with increased microbial biomass N, more root-derived microbial C, and less shoot biomass and root-derived CO2. These findings suggest that P fertilization coupled with C supply from root exudates induced more microbial N immobilization, which reduced the RPE of ryegrass during later stages when soil N limitation negatively impacted plant growth. However, P-induced microbial N immobilization did not affect clover as much because its biological N fixation, on average 37% of total plant N, may have alleviated soil N limitation. We further observed significant positive relationships between excess net soil N and P release and the RPE by Day 58 across all planted treatments, indicating that soil N and P release by plants can be directly linked to rhizosphere C mineralization. Overall, our results demonstrate the importance of C–N–P interactions for understanding the RPE, which have significant implications for P cycling in plant-soil systems.

Rates of dark CO2 fixation are driven by microbial biomass in a temperate forest soil

Soils substantially contribute to the terrestrial fluxes of CO2 to the atmosphere. Dark CO2 fixation, the microbial process by which pore space CO2 is reduced to organic matter, may recycle and trap some of the CO2 respired in soils before it can escape to the atmosphere. To evaluate its potential significance for global temperate forest soil carbon stocks, we quantified dark CO2 fixation rates in a temperate beech forest soil down to 1 m depth over a range of 2–20% (v:v) headspace CO2 concentrations, by tracing incorporation of a13C–CO2 label into microbial biomass carbon and soil organic matter. We found that fixation rates under a concentration of 2% CO2 decreased with depth from 0.86 to 0.06 μg C normalized to g(dw) soil−1 d−1. However, when dark CO2 fixation rates were normalized to soil microbial biomass carbon, no significant differences between depths were observed. Higher CO2 concentrations increased fixation rates, with a linear 2-fold increase between 2% and 10% CO2. Molecular analysis revealed the dominance of heterotrophs, along with the presence of autotrophs mainly employing the Calvin Benson Bassham (CBB) pathway followed by the reductive citric acid (rTCA) pathway. Although community composition varied with depth, the relative fraction of autotrophs determined by qPCR of RuBisCO (cbbL IA, cbbL IC) and ATP-citrate lyase (aclA) genes remained stable at approximately 0.5% of the total community. Dark CO2 fixed carbon accounted for up to 1.1% of microbial biomass carbon and up to 0.035% of soil organic carbon after 28 days. We estimated a fixation flux of 25 ± 7.2 g C m−2 yr−1 to 1 m depth for the Hainich forest soil under field conditions. Without this process, Hainich forest soil CO2 emissions would be 5.6% higher, recycling a fraction of carbon large enough to potentially affect carbon isotope signatures in SOC. If this is held for all temperate forest soils globally, the annual rate of dark CO2 fixation would be 0.26 ± 0.07 Pg C yr−1 to a depth of 1 m, without considering contributions from other biomes. In conclusion, microbial biomass carbon and CO2 concentration appear to be the main drivers of dark CO2 fixation in temperate forest soils, and dark CO2 fixation may maintain Hainich forest soil carbon stocks by moderating a significant fraction of soil CO2 emissions annually.

Methodological clarification for estimating the input of plant-derived carbon in soils under elevated CO2 based on a 13C-enriched CO2 labeling experiment

BACKGROUND AND AIMS: Under the scenario of global change, continuous ¹³C-enriched CO₂ labeling is a powerful tool for evaluating the interaction between plants and soil, especially the influence of elevated CO₂ on the input of plant-derived C (new C) into soil in the short term. However, the methodological validity concerning the acquisition of isotopic signals and their implications in plants and soil remains ambiguous. METHODS: We conducted an experiment simulating elevated CO₂ with wheat planted in growth chambers. ¹³C-enriched CO₂ with identical ¹³C abundance was supplied at two CO₂ concentration levels (350 versus 600 ppm) until wheat harvest. The δ¹³C values of plant tissues and soil were measured periodically during the growing season. RESULTS: The δ¹³C values of wheat tissues under elevated ¹³CO₂ were 15–17% higher than those under ambient ¹³CO₂ after the heading stage, implying that the ¹³C signals themselves in plants and soil were not directly representative of the influence of elevated CO₂ on the C fixation in the plant and thereby the flow of plant-derived C into soil. The proportion of plant-derived C in the soil (fₙₑw) was calculated separately at each CO₂ concentration by taking the initial soil as a reference and the corresponding δ¹³C values as parameters in the mixing model, and we found that elevated CO₂ significantly enhanced the new soil C input by approximately 35.5% during our 62-day labeling. In our experiment, the fₙₑw value under elevated CO₂ could be overestimated by up to 1.7 times if the alteration of ¹³C signatures in photosynthates caused by the change in CO₂ concentration is ignored. CONCLUSIONS: For methodological clarification, we suggest that 1) ¹³C labeling is essential in all CO₂ treatments to achieve CO₂ concentration-dependent ¹³C signals in plants and soil, and that 2) the influence of elevated CO₂ on soil C turnover can be estimated by the difference in the fₙₑw under the two CO₂ concentrations.

Phloem loading in cucumber: combined symplastic and apoplastic strategies.

Phloem loading, as the first step of transporting photoassimilates from mesophyll cells to sieve element-companion cell complex, creates a driving force for long-distance nutrient transport. Three loading strategies have been proposed: passive symplastic loading, apoplastic loading and symplastic transfer followed by polymer-trapping of stachyose and raffinose. Although individual species are generally referred to as using a single phloem loading mechanism, it has been suggested that some plants may use more than one, i.e. 'mixed loading'. Here, by using a combination of electron microscopy, reverse genetics and 14 C labeling, loading strategies were studied in cucumber, a polymer-trapping loading species. The results indicate that intermediary cells (ICs), which mediate polymer-trapping, and ordinary companion cells, which mediate apoplastic loading, were mainly found in the fifth and third order veins, respectively. Accordingly, a cucumber galactinol synthase gene (CsGolS1) and a sucrose transporter gene (CsSUT2) were expressed mainly in the fifth/third and the third order veins, respectively. Immunolocalization analysis indicated that CsGolS1 was localized in companion cells (CCs) while CsSUT2 was in CCs and sieve elements (SEs). Suppressing CsGolS1 significantly decreased the stachyose level and increased sucrose content, while suppressing CsSUT2 decreased the sucrose level and increased the stachyose content in leaves. After 14 CO2 labeling, [14 C]sucrose export increased and [14 C]stachyose export reduced from petioles in CsGolS1i plants, but [14 C]sucrose export decreased and [14 C]stachyose export increased into petioles in CsSUT2i plants. Similar results were also observed after pre-treating the CsGolS1i leaves with PCMBS (transporter inhibitor). These results demonstrate that cucumber phloem loading depends on both polymer-trapping and apoplastic loading strategies.

Carbon Dioxide Promotes Dehydrogenation in the Equimolar C2 H2 -CO2 Reaction to Synthesize Carbon Nanotubes.

The equimolar C2 H2 -CO2 reaction has shown promise for carbon nanotube (CNT) production at low temperatures and on diverse functional substrate materials; however, the electron-pushing mechanism of this reaction is not well demonstrated. Here, the role of CO2 is explored experimentally and theoretically. In particular, 13 C labeling of CO2 demonstrates that CO2 is not an important C source in CNT growth by thermal catalytic chemical vapor deposition. Consistent with this experimental finding, the adsorption behaviors of C2 H2 and CO2 on a graphene-like lattice via density functional theory calculations reveal that the binding energies of C2 H2 are markedly higher than that of CO2 , suggesting the former is more likely to incorporate into CNT structure. Further, H-abstraction by CO2 from the active CNT growth edge would be favored, ultimately forming CO and H2 O. These results support that the commonly observed, promoting role of CO2 in CNT growth is due to a CO2 -assisted dehydrogenation mechanism.

An oxygen isotope chronometer for cellulose deposition: the successive leaves formed by tillers of a C4 perennial grass.

Multiannual time series of (palaeo)hydrological information can be reconstructed from the oxygen isotope composition of cellulose (δ18 OCel ) in biological archives, for example, tree rings, but our ability to temporally resolve information at subannual scale is limited. We capitalized on the short and predictable leaf appearance interval (2.4d) of a perennial C4 grass (Cleistogenes squarrosa), to assess its potential for providing highly time-resolved δ18 OCel records of vapour pressure deficit (VPD). Plants grown at low (0.63kPa) or high (1.58kPa) VPD were swapped between VPD environments and exposed to the new environment for 7d with simultaneous 13 CO2 labelling. Then, leaves were sampled by age/position along individual tillers. Five leaves at different developmental stages were growing simultaneously. The period of most-active leaf elongation, from 10 to 90% of final length, lasted 6.6d, and ~80% of all carbon and oxygen incorporation in whole-leaf cellulose occurred within 7d. Cellulose deposition stopped at (or shortly after) full leaf expansion. The direction of change, low-to-high or high-to-low VPD, had no differential effect on new oxygen and carbon incorporation in cellulose. Successive leaves produced by tillers of C.squarrosa provide a δ18 OCel record useful for reconstructions of short-term hydrological dynamics.

Nitrogen availability alters rhizosphere processes mediating soil organic matter mineralisation

The intrinsic nitrogen (N) supply capacity of soil is central to understanding the productivity of natural plant communities, and essential in the context of determining optimal fertilization rates for agricultural soils. However, it is largely unknown how nutrient availability affects plant mediated priming effects driving soil organic matter mineralisation and associated N-fluxes. We applied continuous, steady-state 13C–CO2 labelling to Lolium perenne grown in high and low productivity grassland soils to allow quantification of SOM- and root-derived soil CO2 efflux. Nutrient treatments (N, P and K) were applied as repeated additions to soils, and impacts on source partitioned soil CO2 efflux were assessed relative to unamended planted and fallow soils. Plants were clipped to uniform height at weekly intervals. Increasing nutrient availability in both soils resulted in a reduction in plant-mediated SOM mineralisation and clipping of plants greatly lowered root-derived respiration but increased SOM mineralisation. Nutrient addition to fallow systems had no effect on SOM mineralisation in either soil. Plant growth stimulated SOM priming, concurrent mobilisation of N from SOM and subsequent plant N uptake in the high productivity soil. Priming was not observed in the low productivity soil due to its greater inherent organic matter stability, resulting in lowered plant-mediated and basal SOM mineralisation. That addition of nutrients reduced SOM mineralisation in planted systems but had no effect in fallow systems is indicative of nutrient availability specifically altering plant-mediated priming of SOM mineralisation. We suggest that plant-soil interactions mediating priming effects are an important determinant of productivity and that the magnitudes of these effects are modified by nutrient availability and soil-specific controls.

Monoterpene 'thermometer' of tropical forest-atmosphere response to climate warming.

Tropical forests absorb large amounts of atmospheric CO2 through photosynthesis but elevated temperatures suppress this absorption and promote monoterpene emissions. Using 13 CO2 labeling, here we show that monoterpene emissions from tropical leaves derive from recent photosynthesis and demonstrate distinct temperature optima for five groups (Groups 1-5), potentially corresponding to different enzymatic temperature-dependent reaction mechanisms within β-ocimene synthases. As diurnal and seasonal leaf temperatures increased during the Amazonian 2015 El Niño event, leaf and landscape monoterpene emissions showed strong linear enrichments of β-ocimenes (+4.4% °C-1 ) at the expense of other monoterpene isomers. The observed inverse temperature response of α-pinene (-0.8% °C-1 ), typically assumed to be the dominant monoterpene with moderate reactivity, was not accurately simulated by current global emission models. Given that β-ocimenes are highly reactive with respect to both atmospheric and biological oxidants, the results suggest that highly reactive β-ocimenes may play important roles in the thermotolerance of photosynthesis by functioning as effective antioxidants within plants and as efficient atmospheric precursors of secondary organic aerosols. Thus, monoterpene composition may represent a new sensitive 'thermometer' of leaf oxidative stress and atmospheric reactivity, and therefore a new tool in future studies of warming impacts on tropical biosphere-atmosphere carbon-cycle feedbacks.

Sulla carnosa modulates root invertase activity in response to the inhibition of long-distance sucrose transport under magnesium deficiency.

Being the principal product of photosynthesis, sucrose is involved in many metabolic processes in plants. As magnesium (Mg) is phloem mobile, an inverse relationship between Mg shortage and sugar accumulation in leaves is often observed. Mg deficiency effects on carbohydrate contents and invertase activities were determined in Sulla carnosa Desf. Plants were grown hydroponically at different Mg concentrations (0.00, 0.01, 0.05 and 1.50mMMg) for one month. Mineral analysis showed that Mg contents were drastically diminished in shoots and roots mainly at 0.01 and 0.00 mM Mg. This decline was adversely associated with a significant increase of sucrose, fructose and mainly glucose in shoots of plants exposed to severe deficiency. By contrast, sugar contents were severely reduced in roots of these plants indicating an alteration of carbohydrate partitioning between shoots and roots of Mg-deficient plants. Cell wall invertase activity was highly enhanced in roots of Mg-deficient plants, while the vacuolar invertase activity was reduced at 0.00mMMg. This decrease of vacuolar invertase activity may indicate the sensibility of roots to Mg starvation resulting from sucrose transport inhibition. 14 CO2 labeling experiments were in accordance with these findings showing an inhibition of sucrose transport from source leaves to sink tissues (roots) under Mg depletion. The obtained results confirm previous findings about Mg involvement in photosynthate loading into phloem and add new insights into mechanisms evolved by S. carnosa to cope with Mg shortage in particular the increase of the activity of cell wall invertase.

CO2 labelling of passenger cars in Europe: Status, challenges, and future prospects

Directive 1999/94/EC requires Member States of the European Union (EU) to ensure that consumers are informed about the fuel consumption and CO2 emissions of new passenger cars. The European Commission is currently evaluating the directive. In support of this effort, we assess the status of car labelling in the EU. We find that all EU Member States have formally implemented national car labelling schemes. However, relevant information is not presented to consumers in a uniform manner. Only 13 Member States have implemented graphic labels that differ in their design, metrics, and classification of vehicles. The fuel consumption data displayed to consumers underrate yearly fuel costs in the order of several hundred Euros per car. We argue that car labelling can be made more effective if Member States adopt: (i) a uniform label that mirrors, as far as feasible, the design of the EU energy label, (ii) data and classification metrics that accurately reflect the fuel consumption and CO2 emissions observed by consumers, and (iii) a labelling scale that allows differentiation between efficient hybrid and plug-in hybrid vehicles. By following these recommendations, the European car labelling can receive wider recognition and foster well-informed consumer choices.