Hydrogen isotope discrimination in higher plants: Correlations with photosynthetic pathway and environment

Summary The ratio of deuterium to hydrogen (expressed as D) in hydrogen released as water during the combustion of dried plant material was examined. The D value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C₃ plants show mean D values of-132 for shoots and -117 for roots; C₄ plants show mean D values of -91 for shoots and-77 for roots and CAM plants a D value of-75 for roots and shoots. The difference between the D value of shoot material from C₃ and C₄ plants was confirmed in species growing under a range of glasshouse conditions. This difference in D value between C₃ and C₄ species does not appear to be due to differences in the D value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C₃ and C₄ plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in D values are discussed. In CAM plants grown in the laboratory or collected from the field D values range from-75 to +50 and are correlated with ¹³C values. When deprived of water, the D value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different D value of available water in areas of increasing aridity. Whatever the origin of the variable D value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.     

Oxygen isotope ratio stratification in a tropical moist forest

Summary Oxygen isotope ratios were determined in leaf cellulose from two plant species at Barro Colorado (Republic of Panama) in 4 different plots, two of which were undergoing an irrigation treatment during the dry season. There is a gradient in ¹⁸O values of leaf cellulose from the understory to canopy leaves, reflecting the differences in relative humidity between these two levels of the forest. This gradient is most pronounced in irrigated plots. For irrigated plots there was a highly significant correlation between ¹⁸O and ¹³C values, which was not observed in control plots. This relationship can be explained by humidity controlling stomatal conductance. Low humidity affects ¹⁸O values of leaf water during photosynthesis, which isotopically labels cellulose during its synthesis. Low humidity also decreases stomatal conductance, which affects discrimination against carbon-13 by photosynthetic reactions, thus affecting the ¹³C values of photosynthates. WUE values calculated by using plant carbon and oxygen isotope ratios were similar to those observed with gas exchange measurements in other tropical and temperate area. Thus the concurrent analysis of carbon and oxygen isotope ratios of leaf material can potentially be useful for long term estimation of assimilation and evapotranspiration regimes of plants.     

Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition

We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (¹³C_POC) and suspended matter (¹³C_POC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest ¹³C_DIC values are observed due to enhanced input of CO₂ from decomposition of ¹³C-depleted terrestrial plant detritus (average ¹³C_DIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative ¹³C_DIC values (average ¹³C_DIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl^–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl^–1. Furthermore, in winter the very narrow range of ¹³C_POC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer ¹³C_POC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in ¹³C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of ¹³C/¹²C fractionation by phytoplankton is attempted.     

Comparisons of δ13C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants

Summary The ¹³C values of submerged aquatic plants from contrasting but relatively defined habitats, and the ¹³C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the ¹³C values of dissolved inorganic carbon in the water were also measured. Plant ¹³C values in the vicinity of-40 to-50 were found in rapidly flowing spring waters with carbonate ¹³C values of-16 to-21, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO₂ via RuP₂ carboxylase. Plant ¹³C values in the vicinity of-10 to-15 in sluggish water with carbonate ¹³C values of about-5 were observed, consistent with the notion that boundary layer diffusion and/or HCO₃ ^- uptake may determine the ¹³C value of submerged aquatic plants in these circumstances. Comparisons of ¹³C values of the same or related species growing in waters of similar carbonate ¹³C value but different flow rates confirmed this view; more negative ¹³C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the ¹³C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The ¹³C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO₂, as opposed to atmospheric carbon. The contributions of these variations in ¹³C of the carbon source, and of isotope fractionation in diffusion, to the ¹³C value of submerged parts of dimorphic plants is discussed.     

Shoot δ15N correlates with genotype and salt stress in barley

Given a uniform N source, the ¹⁵N of barley shoots provided a genotypic range within treatments and a separation between control and salt-stress treatments as great as did ¹³C^*. Plant ¹⁵N has been represented in the literature as a bioassay of external source ¹⁵N and used to infer soil N sources, thus precluding consideration of the plant as a major cause in determining its own 8¹⁵N. We believe this to be the first report of plant ¹⁵N as a genetic trait. No mechanistic model is needed for use of ¹⁵N as a trait in controlled studies; however, a qualitative model is suggested for further testing.Symbol ¹⁵N (or ¹³C) the difference between: (1) the ratio of heavy to light isotopes of the element in a sample and (2) that of its reference standard     

Effects of competition and N and P supply on carbon isotope discrimination and <Superscript>15</Superscript>N-natural abundance in four grassland species

The effect of interspecific competition and element additions (N and P) on four grassland species (Poa pratensis, Lolium perenne, Festuca valida, Taraxacum officinale) grown under field conditions was studied. Two grasses (L. perenne, F. valida) grown in monoculture (absence of competition) showed lower carbon isotope discrimination (¹³C) and enriched ¹⁵N values. Nitrogen addition (as urea) had inconsistent effects on species ¹³C while caused enrichment of ¹⁵N of P. pratensis and F. valida but strong depletion of ¹⁵N of T. officinale. Phosphorous had no significant effect on ¹³C but depleted ¹⁵N of all species.     

Spatial and temporal variation in carbon isotope discrimination in prairie graminoids

We present the results of a 5-year examination of variation in the stable carbon isotope composition () of three C₃ graminoid species from a Sandhills prairie: Agropyron smithii, Carex heliophila and Stipa comata. Although consistent species-specific patterns for mean were seen, there was also significant and substantial among-year and within-season variation in . A smaller contribution to variation in came from topographic variation among sampling sites. Effects of species, year, season and topography contribute to variation in in an additive manner. An association between climate and exists that is consistent with previous work suggesting that reflects the interplay between photosynthetic gas exchange and plant water relations. Within the growing season, the time over which integrates plant response to the environment ranges from days to months.     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Significance of rooting depth in mire plants: Evidence from natural <Superscript>15</Superscript>N abundance

Variation in stable nitrogen isotope ratios (¹⁵N) was assessed for plants comprising two wetland communities, a bog-fen system and a flood plain, in central Japan. ¹⁵N of 12 species from the bog-fen system and six species from the flood plain were remarkably variable, ranging from –5.9 to +1.1 and from +3.1 to +8.7, respectively. Phragmites australis exhibited the highest ¹⁵N value at both sites. Rooting depth also differed greatly with plant species, ranging from 5cm to over 200cm in the bog-fen system. There was a tendency for plants having deeper root systems to exhibit higher ¹⁵N values; plant ¹⁵N was positively associated with rooting depth. Moreover, an increasing gradient of peat ¹⁵N was found along with depth. This evidence, together with the fact that inorganic nitrogen was depleted under a deep-rooted Phragmites australis stand, strongly suggests that deep-rooted plants actually absorb nitrogen from the deep peat layer. Thus, we successfully demonstrated the diverse traits of nitrogen nutrition among mire plants using stable isotope analysis. The ecological significance of deep rooting in mire plants is that it enables those plants to monopolize nutrients in deep substratum layers. This advantage should compensate for any consequential structural and/or physiological costs. Good evidence of the benefits of deep rooting is provided by the fact that Phragmites australis dominates as a tall mire grass.     

δ13C values of grass species collected in the northern Sahara desert

Summary ¹³C values were measured for 45 Poaceae species collected in the northern Sahara desert, at the foot of the Saharan Atlas. The results indicate a clear relationship between carbon isotope discrimination and phytogeographical distribution of the grasses. Mediterranean species predominantly had ¹³C values indicating the C₃ pathway of photosynthesis. By contrast, nearly all species belonging to the Saharo-Arabian and /or Sudanian group showed a C₄ like carbon isotope composition. Leaf material of two species, Lygeum spartum and Stipa tenacissima, had ¹³C values in the region of-20, i.e. intermediate between the mean ¹³C values of C₃ and C₄ plants. However, additional speciments of both these grasses obtained from a different source (herbarium of the Hebrew University, Jerusalem) yielded a C₃ like carbon isotope composition.     

Using stable hydrogen and oxygen isotope measurements of feathers to infer geographical origins of migrating European birds

Successful application of stable-hydrogen isotope measurements (D_f) of feathers to track origins of migratory birds and other wildlife requires a fundamental understanding of the correlation between D_f and deuterium patterns in rainfall (D_p) over continental scales. A strong correlation between D_p and D_f has been confirmed for birds and insects in North America, but not yet for other continents. Here, we compare D_f data from resident European birds to new D_p basemaps for Europe. Three maps, representing growing-season and mean annual D_p estimates from an elevation-explicit, detrended interpolation model and growing-season D_p estimates from simple Kriging, all indicate that strong isotope gradients occur across Europe with a general depletion occurring in a northeast direction. The feather data, representing 141 individuals of 25 avian species from 38 sites, ranged from –131 to –38. Regression analysis showed that strong correlations existed between both mean annual and growing-season D_p estimated by detrended interpolation and D_f of non-aquatic and non-corvid birds (r²=0.66 and 0.65, respectively). We also examined mean annual and growing-season ¹⁸O_p vs. ¹⁸O_f for our samples. Both oxygen regressions were similar (r²=0.56 and 0.57, respectively) but poorer than for deuterium. Our study reveals that D measurements of feathers from migratory birds in Europe may be used to track their origin and movements, and so provide a powerful investigative tool for avian migration research in Europe.     

Skeletal isotope microprofiles of growth perturbations in<Emphasis Type="Italic"> Porites</Emphasis> corals during the 1997–1998 mass bleaching event

Severe coral bleaching occurred throughout the tropics in 1997/98. We report high-resolution skeletal oxygen isotope (¹⁸O) and carbon isotope (¹³C) microprofiles for bleached corals from Pandora Reef, Great Barrier Reef, and Ishigaki Island, Japan, in order to examine the ability of Porites corals to record clear signals of bleaching. Analysis of the annual cycle in ¹⁸O revealed abrupt reductions in skeletal extension immediately after the 1997–98 summer temperature maximum, indicating that bleaching inhibits coral calcification. Skeletal ¹³C in the Ishigaki corals showed lower values during bleaching, indicating depressed coral metabolism associated with a reduction in calcification. In contrast, microprofiles of skeletal ¹³C from the shaded sides of Pandora Reef corals exhibited little change, possibly because algal photosynthesis was already slow prior to bleaching, thus subduing the ¹³C-response to bleaching. Comparison of ¹⁸O microprofiles from bleached corals with instrumental temperature records showed that Porites corals can recover following 5 months with little skeletogenesis. The results indicate that isotopic microprofiling may be the key to identifying gaps in coral growth that are diagnostic of past bleaching events. We have tested this hypothesis using blue UV fluorescent bands to guide us to coral skeleton where isotope microprofiling identifies bleaching events in 1986, 1989, and 1990. These events, detected by proxy, suggest that coral bleaching may have occurred more commonly on Ishigaki Island than previously recorded.     

Diversity,metabolic types and δ13C carbon isotope ratios in the grass flora of Namibia in relation to growth form,precipitation and habitat conditions

The grass flora of Namibia (374 species in 110 genera) shows surprisingly little variation in ¹³C values along a rainfall gradient (50–600 mm) and in different habitat conditions. However, there are significant differences in the ¹³C values between the metabolic types of the C4 photosynthetic pathway. NADP-ME-type C4 species exhibit the highest ¹³C values (–11.7 ) and occur mainly in regions with high rainfall. NAD-ME-type C4 species have significantly lower ¹³C values (–13.4 ) and dominate in the most arid part of the precipitation regime. PCK-type C4 species play an intermediate role (–12.5 ) and reach a maximum abundance in areas of intermediate precipitation. This pattern is also evident in genera containing species of different metabolic types. Within the same genus NAD species reach more negative ¹³C values than PCK species and ¹³C values decreased with rainfall. Also in Aristida, with NADP-ME-type photosynthesis, ¹³C values decreased from –11 in the inland region (600 mm precipitation) to –15 near the coast (150 mm precipitation), which is a change in discrimination which is otherwise associated by a change in metabolism. The exceptional C3 species Eragrostis walteri and Panicum heterostachyum are coastal species experiencing 50 mm precipitation only. Many of the rare species and monotypic genera grow in moist habitats rather than in the desert, and they are not different in their carbon isotope ratios from the more common flora. The role of species diversity with respect to habitat occupation and carbon metabolism is discussed.     

Recorders of reef environment histories: stable isotopes in corals,giant clams,and calcareous algae

Time-series ¹⁸O and ¹³C records from cohabiting massive coralPorites australiensis and giant clamTridacna gigas from the Great Barrier Reed of Australia, and from calcareous green algae in a core through modernHalimeda bioherm accreting in the eastern Java Sea, provide insights into the complex links between environmental factors and stable isotopes imprinted in these reef skeletal materials. The aragonitic coral and giant clam offer 20 years and 15 years of growth history, respectively. The giant clam yields mean ¹⁸O and ¹³C values of-0.5±0.5 and 2.2±0.2 (n=67), which agree well with the predicted equilibrium values. The coral yields mean ¹⁸O and ¹³C values of-5.6±0.5 and-1.8±0.7 (n=84), offering a striking example of kinetic and metabolic fractionation effects. Although both the coral and giant clam harbor symbionts and were exposed to a uniform ambient environment during their growth histories, their distinct isotopic compositions demonstrate dissimilar calcification pathways. The ¹⁸O records contain periodicities corresponding to the alternating annual density bands revealed by X-radiography and optical transmitted light. Attenuation of the ¹⁸O seasonal amplitudes occurring in the giant clam record 8 years after skeletal growth commenced is attributed to a changeover from fast to slow growth rates. Extreme seasonal ¹⁸O amplitudes of up to 2.2 discerned in both the coral and giant clam records exceed the equivalent seasonal temperature contrast in the reef environment, and are caused by the combined effect of rainfall and evaporation during the monsoon and dry seasons, respectively. Thus in addition of being useful temperature recorders, reef skeletal material of sufficient longevity, such asPorites andTridacna, may also indicate rainfall variations. Changing growth rates, determined from the annual growth bands, may exert a primary control on the coral ¹³C record which shows a remarkable negative shift of 1.7 over its growth history, by comparison with only 0.15 negative shift in the contemporaneous giant clam record. Use of coral ¹³C records as proxies of fossil fuel CO₂ uptake by the ocean must be regarded with caution. The ¹⁸O and ¹³C records fromHalimeda are remarkably uniform over 1000 years of bioherm accretion history (¹⁸O=-1.7±0.2; ¹³C=3.9±0.1,n=28), in spite of variable Mg-calcite cements present in the utricles. Most of the cement infilling is probably syndepositional, and both theHalimeda aragonite and the Mg-calcite cements containign 12.3 mole % MgCO₃ are deposited in isotopic equilibrium. Therefore, in favorable circumstances these algal skeletal remains may act as the shallow water analogs of benthic foraminifera in deep sea sediments in recording ambient sea water isotopic composition and temperature.     

Synthesis of Nα,Nδ-dicarbobenzoxy-L-ornithyl-β-alanine benzyl ester,a derivative of salty peptide,in 1,1,1-trichloroethane with polyethylene glycol-modified papain

Summary N,N-Dicarbobenzoxy-L-ornithyl--alanine benzyl ester, a derivative of salty peptide, was synthesized from N,N-dicarbobenzoxy-L-ornithine ethyl ester and -alanine benzyl ester in 1,1,1-trichloroethane using papain modified with polyethylene glycol. The peptide bond formation proceeded in a transparent organic solvent at room temperature and the product was obtained as precipitates from the reaction system.     

Leaf thickness and carbon isotope composition in the Crassulaceae

Summary Measurements of leaf thickness and ¹³C value were obtained for twenty species and three intergeneric hybrids of the Crassulaceae. The data include plants growing in their native habitats and also in greenhouse cultivation. There is a strong relationship between leaf thickness and leaf ¹³C values. The plants with the thickest leaves of ca. 7 to 11 mm had ¹³C values ranging from -11.5 to -13.8. Plants with leaves that were thinner than 2.0 mm all had ¹³C values that were more negative than -23. Plants having intermediate leaf thickness possessed intermediate ¹³C values. The leaf tissue of four genotypes spanning the range of leaf thicknesses all exhibited a two-fold or greater nocturnal increase in titratable acidity. It appears that the differences in leaf thickness and ¹³C values among the tested species are genetically determined.     

Effect of size on the energy acquired in species of the fish from a neotropical reservoir,Brazil

In this paper we analysed autotrophic sources of the carbon ( ¹³C) and the trophic position ( ¹⁵N) of Leporinus friderici in the influence area of Corumbá Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C₄ grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L.friderici in the different size groups analysed. The highest values of ¹³C recorded for middle sized individuals is attributed to the large contribution of C₄ plants in their diet. Small individuals sampled upstream also receive similar contribution from C₄ plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C₄ plants. The ¹³C negative character of small individuals from downstream is due to the larger contribution of C₃ plants (except periphyton). At larger sizes we found intermediate ¹³C values. The ¹⁵N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the ¹³C concentration in the muscle, except for small individuals, when the values were equal.     

Fugu immunoglobulin D: a highly unusual gene with unprecedented duplications in its constant region

We have isolated and characterized the cDNA that encodes IgD of fugu (Takifugu rubripes). Though the splicing of 1 with the 1 domain was similar to those reported for teleost IgDs, highly unusual and unprecedented domain duplications were found in the constant region of the fugu IgD. The structure of the fugu IgD is like VDJ-1-(1-2-3-4-5-6)₂-7-m1-m2. Genomic sequence analysis of the fugu IgD gene supported the results of cDNA sequencing that the first six domains in the constant region are duplicated. Such a novel duplication pattern has not been reported in any other vertebrates. However, IgD secretory domains could not be identified in this study. The deduced amino acid sequence of the fugu IgD constant region showed high identity (35–55%) to the sequences of previously reported teleost IgDs. Gene expression analyses based on RT-PCR demonstrated that the IgD gene is preferentially expressed in presumptive lymphoid tissues; moreover, in situ hybridization showed that IgD-positive cells are distributed throughout the spleen and head kidney. The expression pattern is similar to that of IgM, corroborating the hypothesis that IgD plays an important role in the humoral immune system of this species.The nucleotide sequence data reported in this paper will appear in the DDBJ/EMBL/GenBank nucleotide sequence databases with the accession numbers AB159481 and AB159482.     

Autotrophic carbon sources for heterotrophic bacterioplankton in a floodplain lake of central Amazon

The relative contribution of autotrophic carbon sources (aquatic macrophytes, flooded forest, phytoplankton) for heterotrophic bacterioplankton was evaluated in a floodplain lake of the Central Amazon. Stable carbon isotopes (¹³C) were used as tracers. Values of ¹³C of different autotrophic sources were compared to those of dissolved organic carbon (DOC) and those of bacterially produced CO₂.The percentage of carbon derived from C₄ macrophytes for bacterially produced CO₂ was the highest, on average 89%. The average ¹³C value of CO₂ from bacterial respiration was –18.5 ± 3.3. Considering a fractionation of CO₂ of 3 by bacterial respiration, ¹³C value was –15.5, near C₄ macrophyte ¹³C value (–13.1).The average value of total DOC ¹³C was –26.8 ± 2.4. The percentage of C₄ macrophytes carbon for total DOC was on average 17%. Considering that bacteria consume mainly carbon from macrophytes, the dominance of C₃ plants for total DOC probably reflects a faster consumption of the former source, rather than a major contribution of the latter source.Heterotrophic bacterioplankton in the floodplain may be an important link in the aquatic food web, transferring the carbon from C₄ macrophytes to the consumers.     

Insect food preferences analysed using 13C/12C ratios

Summary Stable carbon isotope ratio analysis is a powerful technique in tracing ecosystem carbon flows, especially those between primary and secondary producers. The distinctive ¹³C/¹²C ratios of plant species tend to pass along the food chain with little further fractionation, hence the stable carbon isotope composition of an animal is an important clue to what it has eaten. We compared the stable carbon isotope composition of plants and insects in an old field in Georgia. Of the dominant plants in the old field, 6 were C₄ species and had ¹³C¹ values of-10.9 to 12.9, and 7 were C₃ species with values of-27.3 to-29.1. Insects known to be feeding on only one plant species had ¹³C values within 1 of the isotopic composition of the plant. Wasp larvae parasitizing two insect species had ¹³C values 1.3 and 1.7 higher than that of the food plant. A variety of insects of unknown food habits collected on monospecific and mixed species plant stands in the old field had ¹³C values ranging from-10.1 to-30.0. Two species of leafhopper and a grasshopper had isotopic compositions within the range of C₄ plant values; a tortoise beetle and a lace bug had isotopic compositions within C₃ plant values. Other insects had intermediate ¹³C values, suggesting a mixed diet composed of both C₃ and C₄ plants. The carbon isotopic ratios of field collected insects appears to be a useful qualitative indicator of their feeding preference.