C3 Plant Material Research Articles

Geochemical signatures (C, N, δ13C, δ15N, metals) of suspended matter in the river Weiße Elster (central Germany): their seasonal and flow-related distribution 1997–2001

Geochemical studies of carbon, nitrogen, δ13C, δ15N as well as Fe, Mn, Cd, Zn, Cr and Hg in suspended matter taken from the river Weiße Elster (central Germany) between 1997 and 2001 reveal significant changes to the composition of the organic sediment load, which correlate with the hydrological period and flow rate. Using C/N ratios and the isotope values of carbon and nitrogen as source indicators, it was found that the organic suspended matter fractions in hydrological winter periods comprise both resuspended mortal plankton material from the riverbed and terrigenous C3 plant material from the clastic input. During the 6 month summer periods, increased bioproductivity results in more dissolved carbon and mineral nitrogen compounds being taken up by the freshly formed aquatic organic substance (freshwater plankton). These compounds stem from bacterial breakdown processes affecting organic components of the river sediment and/or the peripheral soil zone. Increasing fractions of freshwater plankton during the summer period are accompanied by an increase in the nitrogen content and by isotope signatures shifting (δ13C to lower but δ15N to higher values) in the suspended matter. Seasonally opposite correlations between metal contents (e.g. Cd, Zn, Cr, Hg and Fe) and the carbon and nitrogen levels of suspended matter (significantly positive in winter and significantly negative in summer) show that in suspended matter these elements mostly bind to resuspended mortal (rather than the freshly formed living aquatic) organic substance. According to long-term measuring series, between 1993 and 2002 the levels of heavy metals (especially cadmium) in the suspended matter of the river Weiße Elster decreased. Similarly, between 1997 and 2001 the oxygen level in the river Weiße Elster improved. This caused the faster breakdown of organic substance on the riverbed, resulting in the increased uptake of 15N-rich nitrogen compounds into the fresh aquatic organic substance formed every year, and an increase in the conversion of dissolved manganese in the water into insoluble manganese compounds in the river sediment.

??13C VALUES OF ORGANIC CONSTITUENTS AND POSSIBLE SOURCE OF HUMIC SUBSTANCES IN JAPANESE VOLCANIC ASH SOILS

To gain a better understanding about the δ 13 C values of organic constituents and possible source of humic substances in Japanese volcanic ash soils, we determined the δ 13 C values of charred plant fragments, humic and fulvic acids, and whole soils, using 10 volcanic ash soil samples. Furthermore, the characteristics of the humic acid obtained from the dil. H 2 O 2 -treated residues of charred plant materials, which were produced during the burning of a grassland, were compared with those of black (type A) humic acids in volcanic ash soils. The δ 13 C values of the charred plant fragments, humic and fulvic acids, and whole soils studied ranged from -25 to -17%o, -25 to -17‰, -23 to -15%o, and -24 to -17‰, respectively. The δ 13 C values of the whole soils were highly correlated with those of the charred plant fragments (r = 0.968, significant at 0.1% level), humic acids (r = 0.947, significant at 0.1% level) or fulvic acids (r = 0.900, significant at 0.1% level), suggesting that in Japanese volcanic ash soils, the δ 13 C data of whole soils are valuable for discussing and estimating the origin of carbon of charred plant fragments as well as humic and fulvic acids. The δ 13 C values of the charred plant fragments were highly correlated with those of the fulvic acids (r = 0.792, significant at 1% level) and especially humic acids (r = 0.951, significant at 0.1% level). The contribution ratios of C4-plant-derived carbon on the carbon in the charred plant fragments, humic and fulvic acids, and whole soils ranged from 15 to 69%, 16 to 65%, 29 to 86%, and 24 to 66%, respectively. The 13 C-NMR spectrum and X-ray diffraction pattern of the humic acid obtained from the oxidative degradation products of the charred plant materials were similar to those of type A humic acids reported previously. Based on these findings, it was assumed that both charred C3- and C4-plant materials merit close attention as an important source of humic substances in Japanese volcanic ash soils.

Carbon isotopic fractionation during decomposition of plant materials of different quality

Changes in isotopic 13C composition of solid residues and CO2 evolved during decomposition of C3 and C4 plant materials were monitored over 10 months to determine carbon isotopic fractionation at successive stages of biodegradation. We selected plant materials of different chemical quality, e.g., Zea mays (leaves, stems, coarse roots, and fine roots), Lolium perenne (leaves and roots), Pinus pinaster (needles), and Cocos nucifera (coconut shell) and also characterized these by solid‐state 13C NMR. Roots were more lignified than aerial parts of the same species. Lignin was always depleted in 13C (up to 5.2‰) as compared with cellulose from the same sample. Proteins were enriched in 13C in C3 plants but depleted in maize. Cumulative CO2 evolved fitted a double‐exponential model with two C pools of different lability. During early stages of decomposition, the CO2‐C released was usually 13C depleted as compared with the initial substrate but enriched at posterior stages. Consequently, with ongoing decomposition, the solid residue became 13C depleted, which could only partly be explained by an accumulation of lignin‐C. The extension of the initial 13C depleted CO2‐C phase was significantly correlated with the labile substrate C content, acid‐detergent soluble fraction, and total N, pointing to a direct influence of plant quality on C isotopic dynamics during early stages of biodegradation. This isotopic fractionation can also lead to an underestimation of the contribution of plant residues to CO2‐C when incubated in soils. We discuss possible implications of these mechanisms of 13C fractionation in ecosystems.

Stratigraphic carbon isotope fluctuations of detrital woody materials during the Aptian Stage in Hokkaido, Japan: Comprehensive δ13C data from four sections of the Ashibetsu area

Geological and organic geochemical studies were performed on an Aptian (mid-Cretaceous) sedimentary succession of the Sorachi and Yezo groups in the Ashibetsu area, central Hokkaido, northern Japan. Microscopic observations of kerogen samples indicate that the constituents of sedimentary organic matter (SOM) are predominantly detrital woody materials (opaque and translucent phytoclasts). Hydrogen/carbon atomic ratios of the kerogen samples indicate that the SOM have not been affected by thermal alteration significantly and thus preserved the original δ 13C compositions. It is found that δ 13C wood profiles of four sections from the Ashibetsu area fluctuate systematically with stratigraphy. The δ 13C wood profiles show a remarkable negative shift followed by a positive excursion of ∼3.6‰ (from −25.4 to −21.8‰) exhibiting a bifurcate shape in the early Aptian. δ 13C wood values become nearly constant between −23.0 and −23.5‰ and then approximate to ∼−24.0‰ in the late Aptian. A relatively small positive anomaly is also identified in the latest Aptian. The similarity in δ 13C wood profiles among different sections suggests that SOM with homogenized δ 13C values of C3 plants were deposited in sediments. Transportation for a long distance from the sufficiently large provenance is postulated to mix C3 plant materials, resulting in the homogenization of δ 13C wood values. The δ 13C wood profile is essentially conformable with that of Pacific marine carbonates, with their isotopic difference almost constant at all times. Such conformable marine and terrestrial δ 13C variations support the previous hypothesis that the temporal δ 13C change of the Aptian ocean–atmosphere–biosphere system is precisely traced by bulk isotopic analyses of detrital woody materials, and the supplemental paleoenvironmental effects onto δ 13C wood composition, such as pCO 2 changes, are probably negligible.

Nitrogen and carbon stable isotope ratios in the sympatric Australian termites, Amitermes laurensis and Drepanotermes rubriceps (Isoptera: Termitidae) in relation to their feeding habits and the quality of their food materials

Tissue N and C stable isotope ratios of two sympatric termite species were investigated in relation to those of their stored food materials at two savanna sites in north-eastern Australia (Woodstock and Oak Valley). At both sites, the δ 15N values of termite tissues and the stored food materials of the litter-feeding species Amitermes laurensis were significantly greater than their equivalents in the grass-harvesting species Drepanotermes rubriceps. In addition, the carbohydrate/lignin and C/N ratios were higher and chitin/carbohydrate ratios were lower in food materials stored in the mounds of D. rubriceps. Both sets of analyses confirmed that D. rubriceps assimilates less decomposed food materials than A. laurensis. Tissue δ 13C values indicated that both species assimilated similar proportions of C3 and C4 plant materials at the Woodstock site, but that the workers of A. laurensis assimilated a greater proportion of C3 plant material at the Oak Valley site. The δ 15N values of termites from the Woodstock site were significantly greater than those from Oak Valley, although the differences in order at each site were consistent between species. The results indicate that N and C stable isotope ratios must be carefully compared across habitats.

Decomposability of C3 and C4 grass litter sampled under different concentrations of atmospheric carbon dioxide at a natural CO2 spring

Elevated concentrations of atmospheric CO2 can influence the relative proportions, biomass and chemical composition of plant species in an ecosystem and, thereby, the input of litter nutrients to soil. Plant growth under elevated CO2 appears to have no consistent effect on rates of litter decomposition; decomposition can, however, differ in C3 and C4 plant material from the same CO2 environment. We here describe the decomposability of leaf litter of two grass species – the C3 Holcus lanatus L. (Yorkshire fog) and C4 Pennisetum clandestinum Hochst. (kikuyu) - from an unfertilized, ungrazed grassland at a cold CO2 spring in Northland, New Zealand. Decomposability was measured by net CO2–C production from litter incubated for 56 days at 25 °C in a gley soil from the site; net mineral-N production from litter was also determined. Both litter and soils were sampled under `low' and `high' concentrations of atmospheric CO2. Decomposition of H. lanatus litter was greater than that of P. clandestinum litter throughout the 56-day incubation. Decomposition tended to be greater in `high-CO2' than in `low-CO2' H. lanatus litter, but lower in `high-CO2' than `low-CO2' P. clandestinum litter; differences were, however, non-significant after 28 days. Overall, litter decomposition was greater in the `low-CO2' than `high-CO2' soil. Differences in decomposition rates were related negatively to litter N concentrations and positively to C:N ratios, but were not predictable from lignin:total N ratios. Net mineral-N production from litter decomposition did not differ significantly in `high-CO2' and `low-CO2' samples incubated in `low-CO2' soil; in `high-CO2' soil some net immobilization was observed. Overall, results indicate the likely complexity of litter decomposition in the field but, nevertheless, strongly suggest that rates of decomposition will not necessarily decline in a `high-CO2' environment.

The influence of diet on the δ 13C of shell carbon in the pulmonate snail Helix aspersa

The influence of diet and atmospheric CO 2 on the carbon isotope composition of shell aragonite and shell-bound organic carbon in the pulmonate snail Helix aspersa raised in the laboratory was investigated. Three separate groups of snails were raised on romaine lettuce (C3 plant, δ 13C=−25.8‰), corn (C4 plant, δ 13C=−10.5‰), and sour orange ( 12C-enriched C3 plant, δ 13C=−39.1‰). The isotopic composition of body tissues closely tracked the isotopic composition of the snail diet as demonstrated previously. However, the isotopic composition of the acid insoluble organic matrix extracted from the aragonite shells does not track diet in all groups. In snails that were fed corn the isotopic composition of the organic matrix was more negative than the body by as much as 5‰ whereas the matrix was approximately 1‰ heavier than the body tissues in snails fed a diet of C3 plant material. These results indicate that isotopic composition of the organic matrix carbon cannot be used as an isotopic substrate for paleodietary reconstructions without first determining the source of the carbon and any associated fractionations. The isotopic composition of the shell aragonite is offset from the body tissues by 12.3‰ in each of the culture groups. This offset was not influenced by the consumption of carbonate and is not attributable to the diffusion of atmospheric CO 2 into the hemolymph. The carbon isotopic composition of shell aragonite is best explained in terms of equilibrium fractionations associated with exchange between metabolic CO 2 and HCO 3 in the hemolymph and the fractionation associated with carbonate precipitation. These results differ from previous studies, based primarily on samples collected in the field, that have suggested atmospheric carbon dioxide contributes significantly to the shell δ 13C. The culture results indicate that the δ 13C of aragonite is a good recorder of the isotopic composition of the snail body tissue, and therefore a better recorder of diet than is the insoluble shell organic carbon. Because the systematic fractionation of carbon isotopes within the snail is temperature dependent, the δ 13C of the shell could provide an independent technique for estimating paleotemperature changes.

Allocation of particulate organic carbon from different sources in two contrasting estuaries of southeastern U.S.A.

Particulate organic carbon (POC) is an important component in the carbon cycle of estuarine systems. Many studies have utilized carbon isotopic composition (δ13C‐POC) to estimate the origin of POC. Most of the early studies were restricted to areas of minimum terrestrial inputs of POC, whereas later studies used multiple stable isotope analysis. In our study, we assess the proportion of POC from C3 and C4 plants and microalgae in two terrestrially affected, contrasting estuaries of the southeastern U.S.A.: the Altamaha (Piedmont) and the Satilla (blackwater) Rivers. Our analysis was based on a mass balance equation, taking into consideration the estimated amounts of microalgae and C3 and C4 plant material. Analysis of δ13C of extracted chlorophyll a (Chl a) was used to estimate the isotopic signature of microalgae to constrain the three endmember mass balance. The maximum concentration of POC fluctuated between 9 and 11 mg C L−1, coinciding with the period of maximum riverine flow. The POC represented 50–70% of the total organic carbon. However, large fluctuations were observed, suggesting important tidal‐ and wind‐driven resuspension. The δ13C‐POC ranged from −21 to −28‰, being more depleted at lower salinities. This indicates rapid dilution of terrestrially derived material with estuarine‐ or marine‐derived material. The Chl a concentration was maximal during summer in upstream stations of the Altamaha estuary, while the Satilla generally showed a midestuary maximum. The δ13C of Chl a ranged from −20.7 to −31.43‰, indicating isotopically depleted inputs of microalgal‐derived material (MaDM). Our results suggest that MaDM is the dominant component of POC in the Altamaha River during summer, whereas the C3 component is dominant during periods of lower productivity and high flushing. Although MaDM is significant in the Satilla estuary, most of the POC consists of material derived from C3 and C4 plants.

Quantifying Rhizosphere Respiration in a Corn Crop under Field Conditions

AbstractIn order to quantify rhizosphere respiration (Rrh) during the growing season, we monitored the isotope ratio (δ13C) of soil CO2 in a corn (Zea mays L.) crop that was grown on a soil developed from C3 plant material. The Rrh was defined as the sum of CO2 respired by plant roots and CO2 respired by microbes that feed on organic material produced by the roots. The δ13C of soil CO2 in the corn plot changed from an early season low of approximately −20‰, to mid‐season values of approximately −14‰, before declining again at the end of the growing season. In the control plot (no C4 plants present) δ13C values of soil CO2 were significantly lower than values in the corn plot, averaging approximately −22‰ throughout most of the season. We observed no significant change in the δ13C value of soil CO2 in either the corn or control plots during a diurnal sampling period. The value of Rrh was 1.71 g CO2 m−2 d−1 27 d after planting (DAP), reached 10 g CO2 m−2 d−1 at 44 DAP, remained at about that value until 76 DAP, and gradually decreased to 2.6 g CO2 m−2 d−1 at 141 DAP. The CO2 respired by the rhizosphere was equivalent to 18 to 25% of crop net photosynthesis and 24 to 35% of crop net CO2 assimilation during most of the growing season.

Stable‐isotope studies on the collagenic and hydroxylapatite components of fossils: Palaeoecological implications

Collagenic material has been extracted and analysed for stable carbon- and nitrogen-isotope ratios from Henschke Cave, a Late Pleistocene fossil locality, South Australia. The carnivore Thylacoleo carnifex most likely consumed omnivores (Parameles spp.) with a palaeodiet of C3 plant material under a forest canopy, which was also recorded in the herbivores analysed (Macropus spp., Sthenurus spp. and Diprotodon spp.). A forested environment supports previous interpretations of extant fauna and their modern habitats. The presence of negative nitrogen-isotope ratios in herbivores has been interpreted as non-diagenetic on the basis of carbon/nitrogen ratios and amino acid spectra, and in fact may be indicative of acidic soils. Analyses on bone and enamel carbonate hydroxylapatite from the same species support the conclusion that bone is unreliable for palaeoecological and palaeoclimatological research. However, bone carbonate hydroxylapatite may prove valuable in assessing the extent of isotopic fractionation during diagenesis. A review of carbon-isotope analyses on fossil collagenic material and enamel carbonate hydroxylapatite suggests a carnivore-herbivore boundary. The application of this boundary in palaeoecological research requires further investigation. Future palaeoecological research on fossils needs to incorporate stable-isotope analyses on the carbonate hydroxylapatite and collagenic components of fossils.

Carbon cycling in the Amazon River: Implications from the 13C compositions of particles and solutes

The 13C:12C of suspended particu-late organic C (POC), dissolved organic C (DOC), and dissolved inorganic C (DIC) were measured during 1982–1984 at 11 main-channel and 7 tributary stations over an 1,800 km reach of the Amazon River between Vargem Grande and Obidos, Brazil. The measured δ13C range vs. marine carbonate (PDB) was –32 to −26‰ for suspended POC, −30 to −28‰ for DOC, and −26 to −12% for DIC. The δ13C of the fine particulate organic C (FPOC) decreased downriver from Vargem Grande, with values lowest during the falling-water portion of the runoff cycle; these trends were the result primarily of input of 13C-depleted FPOC from tributaries draining the lowland regions of the Amazon basin and floodplain soils. The δ13C of the FPOC at Obidos implies that at least 35% of the POC exported by the Amazon River is derived from the lowland portion of the Amazon basin. The δ13C of DIC decreased downriver with the lowest values measured during falling water; these trends were due primarily to within-river respiration and tributary input. The δ13C of the DIC suggests that ∼40% of the organic matter being respired in the river is C4 plant material derived from floodplain grasses.

The influence of N metabolism and organic acid synthesis on the natural abundance of isotopes of carbon in plants.

This paper relates the 13 C/12 C ratio of C3 plant material relative to that of source CO2 to the N source for growth, the organic N content of the plant, and the extent of organic acid synthesis. The 13 C/12 C ratio is quantified as Δ, defined as (δ13 C substrate -δ13 C product)/(1+δ13 C product), where δ13 C values of substrate or product (i.e. the samples) are defined as [13 C/12 C]sample ]/[(13 C/12 C)standard ]-1. The computation is performed by relating differences in plant composition as a function of N nutrition and acid synthesis to the fraction of plant C which is acquired via Rubisco and via other carboxylases. The fractional contribution of the different carboxylases to C gain is then related, using the known isotopic fractionations exhibited by these carboxylases, in a model to predict the final Δ of the plant (relative to atmospheric CO2 ). Application of this approach to a 'typical' C3 land plant yields predictions of the decrease of Δ relative to a hypothetical case in which all C is fixed via Rubisco. The predicted decreases range from 0-24 %, for NH4 + assimilation (which always occurs in the roots) to 2-80%, for NO3 - assimilation in shoots with the organic acid salt which results from acid-base balance, plus any additional organic acid salts plus free acids for a plant with a basal C:N molar ratio in organic material of 15. Intermediate values are predicted for symbiotic growth with N2 , or where NO3 - assimilation in root or shoot is accompanied by some acid-base regulation via OH- loss to the root medium. Comparison with published data on the difference in Δ of Ricinus communis cultured with NH4 + or NO3 - shows that the measured influence of nitrogen source is in the right direction (NO3 - grown plants with a smaller Δ, i.e. a larger deviation from the value predicted for the absence of non-Rubisco carboxylations) to be explained by the observed difference in composition and hence fractional C contribution by the various carboxylases. However, the effect of N source on Δ is greater than that predicted by the model, i.e. a 2.1 % decrease as opposed to a 0.10 % decrease. It is likely that the major cause of the difference in δ13 C of the plants grown on the two N sources is a change in the ratio of transport and biochemical conductances of leaf photosynthesis. Such a change is quantitatively consistent with the lower water use efficiency of NH4 + -grown plants. The predicted, and observed, changes in Δ as a function of N source are of the same magnitude as those found for C3 terrestrial species grown at different temperatures or photon flux densities, or in environments yielding different water use efficiencies by changing root water supply relative to shoot evaporation potential. Variations in N source should be added to the factors which might alter δ of plants growing in the field.

Stable isotopes of carbon dioxide in soil gas over massive sulfide mineralization at Crandon, Wisconsin

Alpers, C.N., Dettman, D.L., Lohmann, K.C. and Brabec, D., 1990. Stable isotopes of carbon dioxide in soil gas over massive sulfide mineralization at Crandon, Wisconsin. In: S.E. Kesler (Editor), Soil and Rock Gas Geochemistry. J. Geochem. Explor., 38: 69-86. Stable isotope ratios of oxygen and carbon were determined for CO2 in soil gas in the vicinity of the massive sulfide deposit at Crandon, Wisconsin with the objective of determining the source of anomalously high CO2 concentrations detected previously by McCarthy et al. (1986). Values of tSl3C in soil gas CO2 from depths between 0.5 and 1.0 m were found to range from - 12.68%0 to -20.03%0 (PDB). Organic carbon from the uppermost meter of soil has ~ t3C between -24.1 and -25.8%0 (PDB), indicating derivation from plant species with the Ca (Calvin) type of photosynthetic pathway. Microbial decomposition of the organic carbon and root respiration from C3 and C4 (HatchSlack) plants, together with atmospheric CO2 are the likely sources of carbon in soil gas CO2. Values of t~tsO in soil-gas CO2 range from 32 to 38%0 (SMOW). These ~sO values are intermediate between that calculated for CO2 gas in isotopic equilibrium with local groundwaters and that for atmospheric CO2. The 6IS o data indicate that atmospheric CO2 has been incorporated by mixing or diffusion. Any CO2 generated by microbial oxidation of organic matter has equilibrated its oxygen isotopes with the local groundwaters. The isotopic composition of soil-gas CO2 taken from directly above the massive sulfide deposit was not distinguishable from that of samples taken 1 to 2 km away. No enrichment of the t~3C value of soil-gas CO2 was observed, contrary to what would be expected if the anomalous CO2 were derived from the dissolution of Proterozoic marine limestone country rock or of Paleozoic limestone clasts in glacial till. Therefore, it is inferred that root respiration and decay of C3 plant material were responsible for most CO2 generation both in the vicinity of the massive sulfide and in the background area, on the occasion of our sampling. Interpretation of our data is complicated by the effects of rainfall, which significantly reduced the magnitude of the CO2 anomaly. Therefore, we cannot rule out the possible mechanism of carbonate dissolution driven by pyrite oxidation, as proposed by Lovell et al. ( 1983 ) and McCarthy et al. ( 1986 ). Further work is needed on seasonal and daily variations of CO2 concentrations and stable isotope ratios in various hydrogeologic and ecologic settings so that more effective sampling strategies can be developed for mineral exploration using soil gases.

Importance of body tissues as sources of nutrients for milk synthesis in the cow, using 13C as a marker.

1. The proportions of carbon in individual milk constituents derived from feed and body tissues in dairy cows, were estimated by taking advantage of the natural variations which occur in the ratio, 13C:12C present in C3- and C4-plant species. 2. Four cows, which had previously grazed C3 plants (ryegrass (Lolium spp.) and white clover (Trifolium repens)), were accustomed to indoor feeding on a ration of C3-plant material (cut pastures and barley meal). The ration was then changed abruptly to one of C4-plant material (paspalum (Paspalum dilatatum) hay, maize silage and meal) for a period of 8 or 9 d in early and again in late lactation. 3. During early lactation it was estimated that 54% of the C in milk fat was derived from the body fat reserves of high genetic merit cows. Corresponding values for casein and lactose were 34 and 24% respectively, if it is assumed they were derived from body protein reserves. In contrast steam-volatile fatty acids in milk fat were almost entirely derived from dietary sources. 4. The proportional contribution of body-tissue C to individual milk constituents varied considerably between animals, possibly associated with genetic merit or the size of the body reserves available for mobilization. 5. In late lactation, when cows were close to energy and protein balance, contributions of body-tissue C to milk fat, casein and lactose ranged up to 19, 19 and 8% respectively. 6. Estimates of endogenous losses of C in faeces averaged 12 and 9% in early and late lactation respectively, and corresponding values for endogenous urinary C were 23 and 15%.

Stable Carbon Isotopic Evidence for Maize Agriculture in Southeast Missouri and Northeast Arkansas

Analysis of bone collagen extracted from human skeletal remains from archaeological sites dating from the Archaic period through Euro-American settlement provides evidence for the introduction of maize into regional subsistence patterns. Stable carbon isotope ratios of samples from both the eastern Ozarks and the Mississippi River alluvial valley indicate that human populations living prior to ca. A.D. 1000 consumed little or no C4 plant material. In populations dating after ca. A.D. 1000, stable carbon isotope ratios indicate that maize represented a significant part of the human diet throughout the region. The change in dietary patterns coincides with a shift in settlement patterns from dispersed hamlets and small villages to civic-ceremonial centers with associated villages, hamlets, and farmsteads. This isotopic evidence indicates that Emergent Mississippian diets did not include substantial quantities of maize or other C4 plant material.

δ13C values of an herbivore and the ratio of C3 to C4 plant carbon in its diet.

The δ13C values of whole body samples of the beetle Tribolium castaneum are closely correlated with the δ13C values of the plant carbon in its diet. The correlation is always high for diets ranging from 100% C4 to 100% C3 plant material. The degree of correlation is independent of the growth rate of the animals.