Drought Sensitivity of the Carbon Isotope Composition of Leaf Dark-Respired CO2 in C3 (Leymus chinensis) and C4 (Chloris virgata and Hemarthria altissima) Grasses in Northeast China.
ABSTRACT: Whether photosynthetic pathway differences exist in the amplitude of nighttime variations in the carbon isotope composition of leaf dark-respired CO2 (?13Cl) and respiratory apparent isotope fractionation relative to biomass (?R,biomass) in response to drought stress is unclear. These differences, if present, would be important for the partitioning of C3-C4 mixed ecosystem C fluxes. We measured ?13Cl, the ?13C of biomass and of potential respiratory substrates and leaf gas exchange in one C3 (Leymus chinensis) and two C4 (Chloris virgata and Hemarthria altissima) grasses during a manipulated drought period. For all studied grasses, ?13Cl decreased from 21:00 to 03:00 h. The magnitude of the nighttime shift in ?13Cl decreased with increasing drought stress. The ?13Cl values were correlated with the ?13C of respiratory substrates, whereas the magnitude of the nighttime shift in ?13Cl strongly depended on the daytime carbon assimilation rate and the range of nighttime variations in the respiratory substrate content. The ?R,biomass in the C3 and C4 grasses varied in opposite directions with the intensification of the drought stress. The contribution of C4 plant-associated carbon flux is likely to be overestimated if carbon isotope signatures are used for the partitioning of ecosystem carbon exchange and the ?13C of biomass is used as a substitute for leaf dark-respired CO2. The detected drought sensitivities in ?13Cl and differences in respiratory apparent isotope fractionation between C3 and C4 grasses have marked implications for isotope partitioning studies at the ecosystem level.
Project description:Knowledge of carbon isotope fractionation is needed in order to discuss the formation and dissociation of naturally occurring CO<sub>2</sub> hydrates. We investigated carbon isotope fractionation during CO<sub>2</sub> hydrate formation and measured the three-phase equilibria of <sup>12</sup>CO<sub>2</sub>-H<sub>2</sub>O and <sup>13</sup>CO<sub>2</sub>-H<sub>2</sub>O systems. From a crystal structure viewpoint, the difference in the Raman spectra of hydrate-bound <sup>12</sup>CO<sub>2</sub> and <sup>13</sup>CO<sub>2</sub> was revealed, although their unit cell size was similar. The δ<sup>13</sup>C of hydrate-bound CO<sub>2</sub> was lower than that of the residual CO<sub>2</sub> (1.0-1.5‰) in a formation temperature ranging between 226 K and 278 K. The results show that the small difference between equilibrium pressures of ~0.01 MPa in <sup>12</sup>CO<sub>2</sub> and <sup>13</sup>CO<sub>2</sub> hydrates causes carbon isotope fractionation of ~1‰. However, the difference between equilibrium pressures in the <sup>12</sup>CO<sub>2</sub>-H<sub>2</sub>O and <sup>13</sup>CO<sub>2</sub>-H<sub>2</sub>O systems was smaller than the standard uncertainties of measurement; more accurate pressure measurement is required for quantitative discussion.
Project description:Plant isotopic baselines are critical for accurately reconstructing ancient diets and environments and for using stable isotopes to monitor ecosystem conservation. This study examines the stable carbon and nitrogen isotope compositions (<i>δ</i> <sup>13</sup>C, <i>δ</i> <sup>15</sup>N) of terrestrial C<sub>3</sub> plants in Elk Island National Park (EINP), Alberta, Canada, with a focus on plants consumed by grazers. EINP is located in a boreal mixed woodland ecozone close to the transition area between historic wood and plains bison habitats, and is currently home to separate herds of wood and plains bison. For this study, 165 C<sub>3</sub> plant samples (grasses, sedges, forbs, shrubs, and horsetail) were collected from three habitat types (open, closed, and wet) during two seasons (summer and fall). There were no statistically significant differences in the <i>δ</i> <sup>13</sup>C or <i>δ</i> <sup>15</sup>N values of grasses, sedges, shrubs and forbs. On the other hand, plant <i>δ</i> <sup>13</sup>C and <i>δ</i> <sup>15</sup>N values varied among habitats and plant parts, and the values increased from summer to fall. These results have several implications for interpreting herbivore tissue isotopic compositions: (1) consuming different proportions of grasses, sedges, shrubs, and forbs might not result in isotopic niche partitioning, (2) feeding in different microhabitats or selecting different parts of the same types of plants could result in isotopic niche partitioning, and (3) seasonal isotopic changes in herbivore tissues could reflect seasonal isotopic changes in dietary plants rather than (or in addition to) changes in animal diet or physiology. In addition, the positively skewed plant <i>δ</i> <sup>15</sup>N distributions highlight the need for researchers to carefully evaluate the characteristics of their distributions prior to reporting data (<i>e.g</i>., means, standard deviations) or applying statistical models (<i>e.g</i>., parametric tests that assume normality). Overall, this study reiterates the importance of accessing ecosystem-specific isotopic baselines for addressing research questions in archaeology, paleontology, and ecology.
Project description:Plastic materials are widely used in agricultural applications to achieve food security for the growing world population. The use of biodegradable instead of nonbiodegradable polymers in single-use agricultural applications, including plastic mulching, promises to reduce plastic accumulation in the environment. We present a novel approach that allows tracking of carbon from biodegradable polymers into CO<sub>2</sub> and microbial biomass. The approach is based on <sup>13</sup>C-labeled polymers and on isotope-specific analytical methods, including nanoscale secondary ion mass spectrometry (NanoSIMS). Our results unequivocally demonstrate the biodegradability of poly(butylene adipate-<i>co</i>-terephthalate) (PBAT), an important polyester used in agriculture, in soil. Carbon from each monomer unit of PBAT was used by soil microorganisms, including filamentous fungi, to gain energy and to form biomass. This work advances both our conceptual understanding of polymer biodegradation and the methodological capabilities to assess this process in natural and engineered environments.
Project description:Stable carbon isotope analyses of vertebrate hard tissues such as bones, teeth, and tusks provide information about animal diets in ecological, archeological, and paleontological contexts. There is debate about how carbon isotope compositions of collagen and apatite carbonate differ in terms of their relationship to diet, and to each other. We evaluated relationships between ?<sup>13</sup>C<sub>collagen</sub> and ?<sup>13</sup>C<sub>carbonate</sub> among free-ranging southern African mammals to test predictions about the influences of dietary and physiological differences between species. Whereas the slopes of ?<sup>13</sup>C<sub>collagen</sub>-?<sup>13</sup>C<sub>carbonate</sub> relationships among carnivores are ?1, herbivore ?<sup>13</sup>C<sub>collagen</sub> increases with increasing dietary ?<sup>13</sup>C at a slower rate than does ?<sup>13</sup>C<sub>carbonate</sub>, resulting in regression slopes >1. This outcome is consistent with predictions that herbivore ?<sup>13</sup>C<sub>collagen</sub> is biased against low protein diet components (<sup>13</sup>C-enriched C<sub>4</sub> grasses in these environments), and ?<sup>13</sup>C<sub>carbonate</sub> is <sup>13</sup>C-enriched due to release of <sup>13</sup>C-depleted methane as a by-product of microbial fermentation in the digestive tract. As methane emission is constrained by plant secondary metabolites in browse, the latter effect becomes more pronounced with higher levels of C<sub>4</sub> grass in the diet. Increases in ?<sup>13</sup>C<sub>carbonate</sub> are also larger in ruminants than nonruminants. Accordingly, we show that ?<sup>13</sup>C<sub>collagen</sub>-<sub>carbonate</sub> spacing is not constant within herbivores, but increases by up to 5 ‰ across species with different diets and physiologies. Such large variation, often assumed to be negligible within trophic levels, clearly cannot be ignored in carbon isotope-based diet reconstructions.
Project description:Drought stress affects a range of plant processes. It is still not well-known how C<sub>3</sub> and C<sub>4</sub> plants respond to drought. Here, we used a combination of meta-analysis and network analysis to compare the transcriptional responses of <i>Oryza sativa</i> (rice), a C<sub>3</sub> plant, and <i>Zea mays</i> (maize), a C<sub>4</sub> plant, to drought stress. The findings showed that drought stress changes the expression of genes and affects different mechanisms in the C<sub>3</sub> and C<sub>4</sub> plants. We identified several genes that were differentially expressed genes (DEGs) under stress conditions in both species, most of which are associated with photosynthesis, molecule metabolic process, and response to stress. Additionally, we observed that many DEGs physically located within the quantitative trait locus regions are associated with C isotope signature (d<sup>13</sup>C), photosynthetic gas exchange, and root characteristics traits. Through the gene co-expression and differential co-expression network methods, we identified sets of genes with similar and different behaviors among C<sub>3</sub> and C<sub>4</sub> plants during drought stress. This result indicates that mitogen-activated protein kinases (MAPK) signaling pathway plays an important part in the differences between the C<sub>3</sub> and C<sub>4</sub> species. The present study provides a better understanding of the mechanisms underlying the response of C<sub>3</sub> and C<sub>4</sub> plants to drought stress, which may useful for engineering drought tolerance in plants.
Project description:The Permian-Triassic mass extinction was marked by a massive release of carbon into the ocean-atmosphere system, evidenced by a sharp negative carbon isotope excursion. Large carbon emissions would have increased atmospheric pCO<sub>2</sub> and caused global warming. However, the magnitude of pCO<sub>2</sub> changes during the PTME has not yet been estimated. Here, we present a continuous pCO<sub>2</sub> record across the PTME reconstructed from high-resolution δ<sup>13</sup>C of C<sub>3</sub> plants from southwestern China. We show that pCO<sub>2</sub> increased from 426 +133/-96 ppmv in the latest Permian to 2507 +4764/-1193 ppmv at the PTME within about 75 kyr, and that the reconstructed pCO<sub>2</sub> significantly correlates with sea surface temperatures. Mass balance modelling suggests that volcanic CO<sub>2</sub> is probably not the only trigger of the carbon cycle perturbation, and that large quantities of <sup>13</sup>C-depleted carbon emission from organic matter and methane were likely required during complex interactions with the Siberian Traps volcanism.
Project description:It has been challenging to simultaneously improve photosynthesis and stress tolerance in plants. Crassulacean acid metabolism (CAM) is a CO<sub>2</sub>-concentrating mechanism that facilitates plant adaptation to water-limited environments. We hypothesized that the ectopic expression of a CAM-specific phospho<i>enol</i>pyruvate carboxylase (PEPC), an enzyme that catalyzes primary CO<sub>2</sub> fixation in CAM plants, would enhance both photosynthesis and abiotic stress tolerance. To test this hypothesis, we engineered a CAM-specific <i>PEPC</i> gene (named <i>AaPEPC1</i>) from <i>Agave americana</i> into tobacco. In comparison with wild-type and empty vector controls, transgenic tobacco plants constitutively expressing <i>AaPEPC1</i> showed a higher photosynthetic rate and biomass production under normal conditions, along with significant carbon metabolism changes in malate accumulation, the carbon isotope ratio δ<sup>13</sup>C, and the expression of multiple orthologs of CAM-related genes. Furthermore, <i>AaPEPC1</i> overexpression enhanced proline biosynthesis, and improved salt and drought tolerance in the transgenic plants. Under salt and drought stress conditions, the dry weight of transgenic tobacco plants overexpressing <i>AaPEPC1</i> was increased by up to 81.8% and 37.2%, respectively, in comparison with wild-type plants. Our findings open a new door to the simultaneous improvement of photosynthesis and stress tolerance in plants.
Project description:Vanillin (4-hydroxy-3-methoxybenzaldehyde) is one of the most widely used food spices. Aimed at bio-vanillin green production, the natural materials were directly catalytically oxidized efficiently in one pot under low O<sub>2</sub> pressure (0.035 MPa) in the presence of a non-noble metal oxidation combined catalyst (NiCo<sub>2</sub>O<sub>4</sub>/SiO<sub>2</sub> nanoparticles), which showed remarkable advantages of a short synthetic route and less industrial waste. The catalytic system showed good universality to many natural substrates with nearly 100% conversion and 86.3% bio-vanillin yield. More importantly, carbon isotope ratio investigations were employed to verify the origin of the organic matter. One hundred percent <sup>14</sup>C content of the obtained vanillin was detected, which indicated that it was an efficient method to distinguish the vanillin from biomass or fossil materials. Furthermore, the <sup>13</sup>C isotope examination showed effective distinguishing ability for the vanillin from a particular biomass source. The C isotope detection provides an effective method for commercial vanillin identification.
Project description:The end-Permian mass extinction event (∼252 Mya) is associated with one of the largest global carbon cycle perturbations in the Phanerozoic and is thought to be triggered by the Siberian Traps volcanism. Sizable carbon isotope excursions (CIEs) have been found at numerous sites around the world, suggesting massive quantities of <sup>13</sup>C-depleted CO<sub>2</sub> input into the ocean and atmosphere system. The exact magnitude and cause of the CIEs, the pace of CO<sub>2</sub> emission, and the total quantity of CO<sub>2</sub>, however, remain poorly known. Here, we quantify the CO<sub>2</sub> emission in an Earth system model based on new compound-specific carbon isotope records from the Finnmark Platform and an astronomically tuned age model. By quantitatively comparing the modeled surface ocean pH and boron isotope pH proxy, a massive (∼36,000 Gt C) and rapid emission (∼5 Gt C yr<sup>-1</sup>) of largely volcanic CO<sub>2</sub> source (∼-15%) is necessary to drive the observed pattern of CIE, the abrupt decline in surface ocean pH, and the extreme global temperature increase. This suggests that the massive amount of greenhouse gases may have pushed the Earth system toward a critical tipping point, beyond which extreme changes in ocean pH and temperature led to irreversible mass extinction. The comparatively amplified CIE observed in higher plant leaf waxes suggests that the surface waters of the Finnmark Platform were likely out of equilibrium with the initial massive centennial-scale release of carbon from the massive Siberian Traps volcanism, supporting the rapidity of carbon injection. Our modeling work reveals that carbon emission pulses are accompanied by organic carbon burial, facilitated by widespread ocean anoxia.
Project description:<h4>Rationale</h4>Dental calculus (mineralised dental plaque) is composed primarily of hydroxyapatite. We hypothesise that the carbonate component of dental calculus will reflect the isotopic composition of ingested simple carbohydrates. Therefore, dental calculus carbonates may be an indicator for sugar consumption, and an alternative to bone carbonate in isotopic palaeodiet studies.<h4>Methods</h4>We utilised Fourier transform infrared attenuated total reflectance analysis to characterise the composition and crystallisation of bone and dental calculus before isotope analysis of carbonate. Using a Sercon 20-22 mass spectrometer coupled with a Sercon GSL sample preparation system and an IsoPrime 100 dual inlet mass spectrometer plus Multiprep device to measure carbon, we tested the potential of dental calculus carbonate to identify C<sub>4</sub> resources in diet through analysis of δ<sup>13</sup> C values in paired bone, calculus and teeth mineral samples.<h4>Results</h4>The modern population shows higher δ<sup>13</sup> C values in all three tissue carbonates compared to both archaeological populations. Clear differences in dental calculus δ<sup>13</sup> C values are observed between the modern and archaeological individuals suggesting potential for utilising dental calculus in isotope palaeodiet studies. The offset between dental calculus and either bone or enamel carbonate δ<sup>13</sup> C values is large and consistent in direction, with no consistent offset between the δ<sup>13</sup> C values for the three tissues per individual.<h4>Conclusions</h4>Our results support dental calculus carbonate as a new biomaterial to identify C<sub>4</sub> sugar through isotope analysis. Greater carbon fractionation in the mouth is likely due to the complex formation of dental calculus as a mineralized biofilm, which results in consistently high δ<sup>13</sup> C values compared to bone and enamel.