Carbon Isotope Discrimination Values Research Articles

Using foliar δ13C from high‐Andean plants (Silala River basin) as a measure of potential evapotranspiration through water use efficiency

AbstractThe water‐dependent nature of arid ecosystems is closely related to the coupling between energy input through photosynthesis and the loss of water through transpiration (Tr), which can be expressed as water use efficiency (WUE). The relationship, however, between environmental factors and plant physiology in controlling evapotranspiration is not well understood in high‐altitude arid environments. Here, we review the use of carbon isotope fractionation (δ13C) to indirectly track fluctuations in WUE and the use of the portable chamber method to partition landscape actual evapotranspiration (ETa) into Tr and bare soil evaporation (Ebs) in the alluvial deposits of the Silala River, a high elevation watershed located in northern Chile. Landscape ETa was also measured with Eddy covariance (EC) systems in the basin's riparian wetland and alluvial hillslope deposits. Carbon isotope results were consistent with what is known from the literature regarding these high‐elevation ecosystems. WUE, as estimated by carbon isotope discrimination values, decreased in summer (the wet season), and increased in winter at all sites. These results were consistent with the EC measurements. Changes in WUE were much greater in the valley wetlands than along the hillslopes, most likely due to a large drop in available soil moisture along the valley bottom during the dry season. Portable chamber results obtained during summer and winter field campaigns showed that at the landscape scale, hillslope ETa was mainly dominated by bare soil evaporation; and ETa partitioning into Tr and Ebs had a seasonal change.This article is categorized under: Engineering Water > Methods Science of Water > Hydrological Processes

Heritability of Morphophysiological Traits in Popcorn for Drought Tolerance and Their Use as Breeding Indicators of Superior Genotypes

This study aimed to identify the genetic control of morphological, water status, and root traits in four inbred lines and their pre-selected hybrid combinations of popcorn, and to identify the best parents and hybrids. The plants were grown under greenhouse conditions, and with two water conditions—water-stressed (WS) and well-watered (WW). We evaluated shoot biomass (SB), whole plant leaf area (WPLA), chlorophyll content, carbon isotope discrimination, net CO2 assimilation rate, the stomatal conductance, transpiration, cumulative plant transpiration, and root weight density in three sections. The reductions in SB and WPLA are attributed to stomatal causes, given the maintenance of water condition values in water-stressed plants. In fact, the stomata were closed for long periods during plant growth under the water-stressed condition, as indicated by the more negative carbon isotope discrimination values. The root weight density, regardless of soil depth and water conditions, was higher in hybrids. There was a preponderance of non-additive effects in the control of morphological and root traits, especially in the WS condition, and heterosis was shown to be the fundamental strategy for obtaining superior hybrids. For water status traits, it is essential to choose the female parent in the crossing block, given the maternal effect expressed by net CO2 assimilation rate, stomatal conductance, and transpiration.

Stable Soil Moisture Improves the Water Use Efficiency of Maize by Alleviating Short-Term Soil Water Stress.

Weaker temporal variation of soil moisture can improve crop water use efficiency (WUE), but its physiological mechanism was still unclear. To explore the mechanism, an organized experiment was conducted in Beijing from June to September. From the jointing stage to maturity stage of maize, stable soil moisture (SSM) and fluctuating soil moisture (FSM) were established with Pressure Potential Difference-Crop Initiate Drawing Water (PCI) and manual irrigation (MI), respectively, to explore the physiological mechanism of SSM to improve maize WUE. Among them, PCI treatments were set with 3 pressure differences of -5, -10, and -15 kPa, and MI treatment was watering every 3 days with the irrigation amount of 9.3 mm. The results showed that (1) after water treatment, the average soil water content of PCI-5 kPa, PCI-10 kPa, PCI-15 kPa, and MI treatments were 53% field capacity (FC), 47, 38, and 78% FC, respectively. It was SSM with weak temporal variation under PCI treatments, and FSM with medium temporal variation under MI treatment. (2) PCI treatments reduced the content of proline, malondialdehyde, and abscisic acid in each organ of maize. (3) Compared with FSM 78% FC, the maize root activity at the filling stage of 53% FC SSM and 47% FC SSM increased significantly by 57.1 and 28.6%, respectively, and the carbon isotope discrimination value (Δ13C) in bracts of the two treatments increased by 18.3 and 10.4%, respectively. (4) There was a very significant positive correlation between WUE based on biomass (WUEb) and Δ13C in bracts. In conclusion, a large temporal variation of soil moisture was an important factor that caused water stress in maize. Under SSM treatments, the accumulation of abscisic acid, proline, and malondialdehyde was synergistically reduced. SSM improved the WUE of maize by alleviating short-term soil water stress caused by the fluctuation of soil moisture.

Pacific Northwest Plants Record Multiannual Atmosphere–Ocean Circulation Patterns

AbstractCarbon isotope ecology can be used as a measure of plant water stress. Plant water stress is complicated: multiple factors (e.g., evapotranspiration rates, temperature, precipitation, soil texture, and available water) control the magnitude of the isotopic expression. Often, large ocean–atmosphere pressure systems result in the convergence of constructive climate parameters that result in increased plant water stress; for example, El Niño and Pacific Decadal Oscillation (PDO) anomaly phases. We examined the biogeochemistry of three species (Thuja plicata: with a Pacific coastal habitat, Thuja occidentalis: native to the Great Lakes region, and Populus tremuloides: a cosmopolitan species found throughout North America). Coincident analyses of these species allowed for intercomparison between plants in habitats directly impacted by atmospheric–oceanic controls on water availability and those out of Pacific impact range. There are oscillatory patterns in the carbon isotope discrimination values (Δ13Cleaf) of Thuja plicata, but no clear patterns in Δ13Cleaf values of the other species. We compare the pattern in isotope discrimination of T. plicata with Pacific‐driven multiannual environmental phenomena to determine whether these patterns could be related to the oscillation in Δ13Cleaf values. The data demonstrate a regular and significant 14‐ to 19‐year periodicity, aligning most closely with PDO climate patterns. Thuja plicata likely records prolonged stress, like plant available water shortages, which coincide with PDO‐associated shifts in precipitation, humidity, and evapotranspiration. These findings demonstrate that coastal Pacific ecosystems are vulnerable to changes in water availability connected to Pacific teleconnections, providing a new recording tool to examine multiannual climate anomalies.

Genetics components of rice root architecture and carbon isotopic fractionation parameters: a tracer for breeding in a water-saving irrigation management

Phenotyping is the major bottleneck in the effort to develop varieties of rice (Oryza sativa L.) suitable for growing under a water-saving irrigation management, such as alternate wetting and drying irrigation techniques (AWD). To analyze if the genotypic variability for carbon isotope discrimination (CID) in rice leaves could be used as a relatively high-throughput tracer to early select superior genotypes highlighting improved root architecture traits when submitted to AWD, a set of twenty varieties grown under semi-natural conditions were submitted to two water irrigation regimes, continuous flooding (CF) and AWD cycles. Coefficients of genetic variance (π2g) obtained for root architecture, micro-morphological and physiological traits were significant for all of them regardless of the adopted irrigation system, except to mean root diameter. The three significant principal components (PCs) with eigenvalue > 1, explain most of the total variation across cycles and water regimes. For most of analyzed traits, the values of heritability coefficients were higher regardless of adopted irrigation management and trait category; for CID, the magnitudes of broad heritability at an individual level (greater than 0.80) were similar in the two irrigation techniques, evidencing that the success of the selection is independent of irrigation management. The higher CID values after three AWD cycles are associated with varieties with higher total root length and volume. To our knowledge, this is the first study demonstrating the potential application of CID as a tracer to select root architecture traits in rice when water-saving irrigation management is of concern.

Isotopic fingerprints of mountain uplift and global cooling in paleoclimatic and paleoecological records from the northern Tibetan Plateau

Post-middle Miocene changes in climate and ecology in the northern Tibetan Plateau have been attributed to tectonic uplift and global climate change. However, the relative roles of tectonism and global climate change have been a long-standing debate. To untangle the complex influences of global climate change versus the tectonism on regional climate and ecology in the northern Tibetan Plateau, we studied carbon isotopes (δ13Cwax) of leaf wax long-chain n-alkanes and carbon (δ13C) and oxygen isotopes (δ18O) of carbonates from three stratigraphic successions (ca. 16 Ma to 2 Ma) in the Hexi Corridor (foreland basin) and compare them with paleoclimate records in the Qaidam Basin (intermontane basin). Our isotopic results can be divided into two stages. In Stage 1 (16–12 Ma), a decrease of δ13Cwax values in the Hexi Corridor and Qaidam Basin is synchronous with global cooling after the Mid-Miocene Climate Optimum (MMCO). We interpret the 2‰ decrease in δ13Cwax values to be associated with the decline in C4 plants due to the global cooling. In Stage 2 (since 12 Ma), plant carbon isotope discrimination (ƐCO2-wax) and δ18O values in the Hexi Corridor reflect relatively stable hydroclimate condition, which contracts with the enhanced aridity in Qaidam Basin during the same interval. We attribute the difference in paleohydrological conditions to the uplift-induced basin isolation and the enhancement of water deficiency in the Qaidam Basin. The effects of late Miocene uplift also manifest as persistent intra-basinal differences in the Hexi Corridor, indicating changes associated with orographic precipitation and ecology.

Genetic variation in carbon isotope discrimination-based water use efficiency of teak (Tectona grandis L. f.) and its association with growth and wood quality traits

Teak (Tectona grandis L. f.) is one of the most preferred tropical timber species for afforestation, reforestation, and commercial plantation in the world. In the event of global warming caused by projected climate change, water-use-efficient teak planting stock would become essential for breeding and plantation activities. To characterize and to evaluate the association of water-use efficiency (WUE) with other growth and wood quality traits, we measured height, girth at breast height (GBH), wood density (WD), and carbon isotope discrimination (CID) values of 162 teak plus trees in a national teak germplasm bank (NTGB). The genetic diversity and structure of these accessions were also confirmed through 21 microsatellite markers for confirmation of their representation of teak meta-population in India. Results indicate 30.43% variation in average height (11.17 ± 3.40 m), 25.51% variation in GBH (67.18 ± 17.14 cm), and 7.48% variation in WD (789.24 ± 59.04 kg/m3) among the accessions. The accessions exhibited a significantly high level of genetic polymorphism (88.74%) with a moderate level of Shannon’s diversity index (0.53) and comparatively low heterozygosity (0.27). No significant correlation was found between height and GBH with the CID values. This confirms that the measurement of growth and wood quality traits in teak alone is not helpful to tree breeders for indirect selection of water-use efficient trees. Rather, assessment of more specific traits related to growth, wood quality, and WUE of teak in different locales will be required to improve the teak germplasm in India.

A low CO2-responsive mutant of Setaria viridis reveals that reduced carbonic anhydrase limits C4 photosynthesis.

In C4 species, β-carbonic anhydrase (CA), localized to the cytosol of the mesophyll cells, accelerates the interconversion of CO2 to HCO3–, the substrate used by phosphoenolpyruvate carboxylase (PEPC) in the first step of C4 photosynthesis. Here we describe the identification and characterization of low CO2-responsive mutant 1 (lcr1) isolated from an N-nitroso-N-methylurea- (NMU) treated Setaria viridis mutant population. Forward genetic investigation revealed that the mutated gene Sevir.5G247800 of lcr1 possessed a single nucleotide transition from cytosine to thymine in a β-CA gene causing an amino acid change from leucine to phenylalanine. This resulted in severe reduction in growth and photosynthesis in the mutant. Both the CO2 compensation point and carbon isotope discrimination values of the mutant were significantly increased. Growth of the mutants was stunted when grown under ambient pCO2 but recovered at elevated pCO2. Further bioinformatics analyses revealed that the mutation has led to functional changes in one of the conserved residues of the protein, situated near the catalytic site. CA transcript accumulation in the mutant was 80% lower, CA protein accumulation 30% lower, and CA activity ~98% lower compared with the wild type. Changes in the abundance of other primary C4 pathway enzymes were observed; accumulation of PEPC protein was significantly increased and accumulation of malate dehydrogenase and malic enzyme decreased. The reduction of CA protein activity and abundance in lcr1 restricts the supply of bicarbonate to PEPC, limiting C4 photosynthesis and growth. This study establishes Sevir.5G247800 as the major CA allele in Setaria for C4 photosynthesis and provides important insights into the function of CA in C4 photosynthesis that would be required to generate a rice plant with a functional C4 biochemical pathway.

Transgenic chickpea (Cicer arietinum L.) harbouring AtDREB1a are physiologically better adapted to water deficit

BackgroundChickpea (Cicer arietinum L.) is the second most widely grown pulse and drought (limiting water) is one of the major constraints leading to about 40–50% yield losses annually. Dehydration responsive element binding proteins (DREBs) are important plant transcription factors that regulate the expression of many stress-inducible genes and play a critical role in improving the abiotic stress tolerance. Transgenic chickpea lines harbouring transcription factor, Dehydration Responsive Element-Binding protein 1A from Arabidopsis thaliana (AtDREB1a gene) driven by stress inducible promoter rd29a were developed, with the intent of enhancing drought tolerance in chickpea. Performance of the progenies of one transgenic event and control were assessed based on key physiological traits imparting drought tolerance such as plant water relation characteristics, chlorophyll retention, photosynthesis, membrane stability and water use efficiency under water stressed conditions.ResultsFour transgenic chickpea lines harbouring stress inducible AtDREB1a were generated with transformation efficiency of 0.1%. The integration, transmission and regulated expression were confirmed by Polymerase Chain Reaction (PCR), Southern Blot hybridization and Reverse Transcriptase polymerase chain reaction (RT-PCR), respectively. Transgenic chickpea lines exhibited higher relative water content, longer chlorophyll retention capacity and higher osmotic adjustment under severe drought stress (stress level 4), as compared to control. The enhanced drought tolerance in transgenic chickpea lines were also manifested by undeterred photosynthesis involving enhanced quantum yield of PSII, electron transport rate at saturated irradiance levels and maintaining higher relative water content in leaves under relatively severe soil water deficit. Further, lower values of carbon isotope discrimination in some transgenic chickpea lines indicated higher water use efficiency. Transgenic chickpea lines exhibiting better OA resulted in higher seed yield, with progressive increase in water stress, as compared to control.ConclusionsBased on precise phenotyping, involving non-invasive chlorophyll fluorescence imaging, carbon isotope discrimination, osmotic adjustment, higher chlorophyll retention and membrane stability index, it can be concluded that AtDREB1a transgenic chickpea lines were better adapted to water deficit by modifying important physiological traits. The selected transgenic chickpea event would be a valuable resource that can be used in pre-breeding or directly in varietal development programs for enhanced drought tolerance under parched conditions.

Spatial variability in foliar carbon and nitrogen isotope values on Tenerife reflects both climate and soils: Establishing a framework for future work

Tenerife Island is well-known for its biodiversity. It boasts the highest elevation in the Atlantic Ocean and its northern and southern slopes have varying moisture and temperature gradients. Consequently, there are multiple spatially discrete vegetation zones, or biomes, recognized on the island that roughly follow elevation. We investigated the extent to which climatic variables as well as soil nitrogen isotope values (δ15N) and weight %N influence spatial isotopic variability in C3 plants during the rainy season and assessed the degree to which foliar carbon isotope discrimination (Δleaf) and δ15N values are able to distinguish biomes. Mean Annual Precipitation explained 71% and 55% of the spatial variability in Δleaf and δ15N values, respectively. Overall, foliar δ15N values tracked those in soils, and soil %N was negatively correlated with both soil and foliar δ15N values. However, there was considerable variability among co-occurring species, as well as among sites within the same biome, which obscured trends among biomes. As a result, only a few biomes were isotopically distinct: Broad-leaved evergreen forest and sub-desert coastal scrub on the northern slope, and summit scrub and sub-desert coastal scrub on the southern slope. Further investigation into the influence of coastal orientation, topography, plant physiology, soil characteristics, as well as seasonal and inter-annual climate variability on foliar isotope values would be fruitful. Nevertheless, these results provide baseline information for researchers seeking to interpret diet and mobility of animals and people, as well as environmental changes over time on Tenerife and other Macaronesian volcanic islands.

Participation of Green Organs to Grain Filling in Triticum turgidum var durum Grown under Mediterranean Conditions.

In wheat, flag leaf, stem, chaff and awns contribute to grain filling through photosynthesis and/or re-mobilization. Environmental and genetic effects on the relative contribution of each organ were examined by analyzing the consequences of sink-source manipulations (shading and excision) and by comparing carbon isotope discrimination (Δ) values in dry matter (at maturity) and sap (two weeks after anthesis) in six durum wheat genotypes grown in two contrasting seasons. The contribution of flag leaf, stem, chaff and awns to grain filling, estimated by sink-source manipulations, highly varied with the season. The contribution of ear photosynthesis and re-mobilization from the stem increased with post-anthesis water stress. They showed a large genetic variation that was, however, not clearly associated to morphological characteristics of ear and stem. Isotopic imprints of chaff on grain Δ were identified as a possible surrogate of the destructive and cumbersome sink-source manipulations to evaluate the contribution of carbon assimilated in ears or re-mobilized from stem. This might facilitate screening of genetic resources and allow the combining of favourable drought tolerance mechanisms in wheat.

Screening for Natural Variation in Water Use Efficiency Traits in a Diversity Set of Brassica napus L. Identifies Candidate Variants in Photosynthetic Assimilation.

Seed yield and quality of crop species are significantly reduced by water deficit. Stable isotope screening (δ13C) of a diversity set of 147 accessions of Brassica napus grown in the field identified several accessions with extremes in water use efficiency (WUE). We next conducted an investigation of the physiological characteristics of selected natural variants with high and low WUE to understand how these characteristics translate to differences in WUE. We identified an interesting Spring accession, G302 (Mozart), that exhibited the highest WUE in the field and high CO2 assimilation rates coupled with an increased electron transport capacity (Jmax) under the imposed conditions. Differences in stomatal density and stomatal index did not translate to differences in stomatal conductance in the investigated accessions. Stomatal conductance response to exogenous ABA was analyzed in selected high and low WUE accessions. Spring lines showed little variation in response to exogenous ABA, while one Semi-Winter line (SW047) showed a significantly more rapid response to exogenous ABA, that corresponded to the high WUE indicated by δ13C measurements. This research illustrates the importance of examining natural variation at a physiological level for investigation of the underlying mechanisms influencing the diversity of carbon isotope discrimination values in the field and identifies natural variants in B. napus with improved WUE and potential relevant traits.

Carbon Stable Isotope Analysis for Glucose in Sake: Simple Freeze-Dried Sake Can Substitute for Glucose Following HPLC Isolation

Carbon stable isotope analysis of ethanol is an established method for determining the authenticity of alcoholic beverages, but there is no accepted method for measurements of glucose carbon stable isotopic composition (δ 13C). This study aims to establish two methods to determine accurately the δ 13C value of glucose isolated from sake by high-performance liquid chromatography (HPLC) after three clean-up steps using ion exchange chromatography and in simple freeze-dried sake (total nonvolatile matter) and to examine two methods that yield different δ 13C values. In the glucose isolation procedure, the δ 13C values of glucose were not significantly affected by the glucose concentration, solvent (water or aqueous acetonitrile), drying method (freeze-dry or nitrogen-spraying), the clean-up step using ion exchange chromatography (weakly acidic cation-exchange, strongly acidic cation-exchange, and weakly basic anion-exchange resins), or HPLC isolation. Glucose nitrogen spray-dried after isolation by ion exchange chromatography and HPLC showed a carbon isotope discrimination value of <0.1 ‰. The glucose δ 13C values ranged from −26.8 to −25.5 ‰ in authentic sake and from −27.0 to −11.0 ‰ in commercial sake samples. This HPLC isolation approach may provide a first step toward visualizing the brewing process via isotopic carbon flow during fermentation. Additionally, there was no significant difference between the δ 13C values of glucose and total nonvolatile matter from sake. The δ 13C measurement of simple freeze-dried sake can substitute for glucose δ 13C measurement using HPLC isolation, thus aiding high-throughput detection of carbon derived from C4 plants in sake.

Inhibition of ethylene synthesis reduces salt-tolerance in tomato wild relative species Solanum chilense

Exposure to salinity induces a burst in ethylene synthesis in the wild tomato halophyte plant species Solanum chilense. In order to gain information on the role of ethylene in salt adaptation, plants of Solanum chilense (accession LA4107) and of cultivated glycophyte Solanum lycopersicum (cv. Ailsa Craig) were cultivated for 7days in nutrient solution containing 0 or 125mM NaCl in the presence or absence of the inhibitor of ethylene synthesis (aminovinylglycine (AVG) 2μM). Salt-induced ethylene synthesis in S. chilense occurred concomitantly with an increase in stomatal conductance, an efficient osmotic adjustment and the maintenance of carbon isotope discrimination value (Δ13C). In contrast, in S. lycopersicum, salt stress decreased stomatal conductance and Δ13C values while osmotic potential remained higher than in S. chilense. Inhibition of stress-induced ethylene synthesis by AVG decreased stomatal conductance and Δ13C in S. chilense and compromised osmotic adjustment. Solanum chilense behaved as an includer and accumulated high amounts of Na in the shoot but remained able to maintain K nutrition in the presence of NaCl. This species however did not stimulate the expression of genes coding for high-affinity K transport but genes coding for ethylene responsive factor ERF5 and JREF1 were constitutively more expressed in S. chilense than in S. lycopersicum. It is concluded that ethylene plays a key role in salt tolerance of S. chilense.

Identification of genotypes for high water use efficiency and root traits in castor (Ricinus communis L.)

Castor (Ricinus communis L.) is an important non-edible oilseed crop of the world. Under rainfed situations the crop yields are low. Crop improvement programmes aim at improvement in seed yield, oil content and tolerance to biotic and abiotic stresses. Traits that contribute to water use efficiency (WUE) and improved productivity have not been adequately characterized in castor. In the present study, thirty five genotypes of castor were grown in a temporarily constructed elevated root study structure to characterize for superior shoot and root systemarchitectural (RSA) traits. Genotypes showed variation in characters that contributed to superior WUE and seed yield. Extrinsic WUE recorded with photosynthetic system ranged between 2.63 to 16.76 µmol CO2/mmol H2O. Intrinsic WUE values ranged between 36.1 to 53.3 µmol CO2 /mmol H2O. Photosynthesis and stomatal conductance values recorded ranged from13.1 to 21.6 µmol CO2 /m2 /s and 0.521to 0.647 mmol H2O/m2 /s. Greening index (SCMR) values ranged between 37 to 54. High Greening index was recorded in RG-48, Kranthi, PCS-230, SKI-215 and Haritha. SLA values ranged between 2.29 to 5.23 dm2 /g. Low SLA typesinclude RG-48, Kranthi, PCS-230, SKI-215 and Haritha. Carbon isotope discrimination (CID) value ranged between 17.49 to 19.52 per mill. Low discrimination to ª 13C included genotypes PCS-330, Kranthi, PCS-230 and PCS-265. Tap root length ranged from 67 to 234 cm. Long tap root was recorded in PCS 324, Haritha, Kranthi, PCS-171, PCS 328, PPL 109, RG-47, RG-48 and SKI-215. Total root volume ranged from 34 to 276 cm3. TDM ranged from 93.4 to 338.7 g. Seed yield ranged from 52 to 163 g/plant. Kranthi, RG-48, Haritha, PCS 171, PCS-230 and SKI-215 showed four to seven superior shoot root and seed yield characters have been proposed as superior WUE genotypes.

Ecophysiological performance of a threatened shrub under restored and natural conditions in a harsh tropical mountaintop environment

Ecophysiological responses of plants are useful for monitoring the success of ecological restoration projects that target species conservation. In this study we evaluated the ecophysiological traits of individuals of Chamaecrista semaphora from a natural population and from a site under restoration. Water potential and chlorophyll a fluorescence parameters were measured both in adult and young plants of the two populations. No difference in water potential was found between sites, but individuals in the restored site had higher water potential at predawn. Adults in the natural site presented lower daily values of potential quantum yield, indicating the occurrence of photoinhibition. Individuals in the restored site also presented higher maximum relative electron transport rate (ETRMAX). No difference was found in leaf carbon isotope discrimination values (σ13C) between plants growing in restored and natural sites, suggesting similar water use efficiency. These results indicate that C. semaphora individuals in the restored site had similar or better photosynthetic and water economy performances than individuals at the natural site. Methodologies traditionally employed to assess stress response of plants, such as chlorophyll a fluorescence and procedures used to evaluate the efficiency of water use, allowed us to verify the success of restoration procedures using an endangered species.

The key factor limiting plant growth in cold and humid alpine areas also plays a dominant role in plant carbon isotope discrimination

Many environmental factors affect carbon isotope discrimination in plants, yet the predominant factor influencing this process is generally assumed to be the key growth-limiting factor. However, to our knowledge this hypothesis has not been confirmed. We therefore determined the carbon isotope composition (δ13C) of plants growing in two cold and humid mountain regions where temperature is considered to be the key growth-limiting factor. Mean annual temperature (MAT) showed a significant impact on variation in carbon isotope discrimination value (Δ) irrespective of study area or plant functional type with either partial correlation or regression analysis, but the correlation between Δ and soil water content (SWC) was usually not significant. In multiple stepwise regression analysis, MAT was either the first or the only variable selected into the prediction model of Δ against MAT and SWC, indicating that the effect of temperature on carbon isotope discrimination was predominant. The results therefore provide evidence that the key growth-limiting factor is also crucial for plant carbon isotope discrimination. Changes in leaf morphology, water viscosity and carboxylation efficiency with temperature may be responsible for the observed positive correlation between Δ and temperature.

Invited review: climate change impacts in polar regions: lessons from Antarctic moss bank archives.

Mosses are the dominant plants in polar and boreal regions, areas which are experiencing rapid impacts of regional warming. Long-term monitoring programmes provide some records of the rate of recent climate change, but moss peat banks contain an unrivalled temporal record of past climate change on terrestrial plant Antarctic systems. We summarise the current understanding of climatic proxies and determinants of moss growth for contrasting continental and maritime Antarctic regions, as informed by 13C and 18O signals in organic material. Rates of moss accumulation are more than three times higher in the maritime Antarctic than continental Antarctica with growing season length being a critical determinant of growth rate, and high carbon isotope discrimination values reflecting optimal hydration conditions. Correlation plots of 13C and 18O values show that species (Chorisodontium aciphyllum / Polytrichum strictum) and growth form (hummock / bank) are the major determinants of measured isotope ratios. The interplay between moss growth form, photosynthetic physiology, water status and isotope composition are compared with developments of secondary proxies, such as chlorophyll fluorescence. These approaches provide a framework to consider the potential impact of climate change on terrestrial Antarctic habitats as well as having implications for future studies of temperate, boreal and Arctic peatlands. There are many urgent ecological and environmental problems in the Arctic related to mosses in a changing climate, but the geographical ranges of species and life-forms are difficult to track individually. Our goal was to translate what we have learned from the more simple systems in Antarctica, for application to Arctic habitats.

Biochemical, physiological and isotopic responses to natural product p-hydroxybenzoic acid in Cocksfoot (Dactylis glomerata L.)

The present study was conducted to evaluate the role of natural compound p-hydroxybenzoic acid (pHBA) on physiological, biochemical and isotopic responses of Dactylis glomerata L. Application of pHBA in the range 0.5–1.5 mM reduced the leaf fresh/dry biomass, shoot/root length, relative water content and leaf osmotic potential of D. glomerata. pHBA decreased the photosynthetic efficiency and quantum yield of photosystem II photochemistry in D. glomerata seedlings following treatment at all concentrations. Photochemical and non-photochemical fluorescence quenching were reduced after treatment with 1.5 mM pHBA. Carbon isotope composition ratio in D. glomerata leaves was significantly less negative following treatment with pHBA than the control. Carbon isotope discrimination value was declined by pHBA. The leaf protein content was lower after treatment with 1.5 mM pHBA. Our results suggest that pHBA possesses allelopathic potential against D. glomerata and this study provide new insights into the physiological, biochemical and isotopic action mechanism of pHBA.

Spider&amp;delta;: an empirical method to extrapolate grapevine (&lt;em&gt;Vitis vinifera&lt;/em&gt; L.) water status at the whole denomination scale using &amp;delta;&lt;sup&gt;13&lt;/sup&gt;C as ancillary data

&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Aims&lt;/strong&gt;: The aim of this study is to test a method to extrapolate vine water status (estimated by the water potential; &lt;strong&gt;Ψ&lt;/strong&gt;) over a whole appellation (protected geographical indication). The spatial extrapolation is based on an empirical approach that combines a reference site (baseline measurements) and carbon isotope discrimination (δ&lt;sup&gt;13&lt;/sup&gt;C) values as ancillary data (AD).&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Methods and results&lt;/strong&gt;: Experiments were conducted on the whole Tavel appellation (Gard, France). The study focused on the dominant variety: Grenache. &lt;strong&gt;Ψ&lt;/strong&gt; was measured as predawn leaf water potential and was monitored over three consecutive years, 2008, 2009 and 2010, on 10, 24 and 24 sites, respectively. δ&lt;sup&gt;13&lt;/sup&gt;C measurements were made at harvest in 2010 on the 24 sites. The spatial model (SPIDERδ) was calibrated using Ydata from 2009 and 2010 and δ&lt;sup&gt;13&lt;/sup&gt;C data from 2010. The quality of prediction was tested on the 2008 data, considered as an independent data set. The results show that SPIDERδ was relevant in estimating &lt;strong&gt;Ψ&lt;/strong&gt; at the whole appellation scale. The extrapolation model significantly improves the prediction (R² = 0.88) compared to a conventional method based on &lt;strong&gt;Ψ&lt;/strong&gt; averages across the appellation (R² = 0.66).&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Conclusion&lt;/strong&gt;: Based on a single measurement taken at time «t» on a reference site, SPIDERδ makes it possible to estimate &lt;strong&gt;Ψ&lt;/strong&gt; on all sites where a δ&lt;sup&gt;13&lt;/sup&gt;C value is available. The use of AD like δ&lt;sup&gt;13&lt;/sup&gt;C makes it possible to consider the spatial extrapolation of &lt;strong&gt;Ψ&lt;/strong&gt; with higher spatial resolution than when only direct measurements are used to calibrate the model.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Significance and impact of the study&lt;/strong&gt;: This work demonstrates the value of using an AD like δ&lt;sup&gt;13&lt;/sup&gt;C to assess &lt;strong&gt;Ψ&lt;/strong&gt; at a scale larger than the single field. This significant result opens the door to the practical use of spatial extrapolation models with higher spatial resolution.&lt;/p&gt;