13C Isotopes

Os isótopos estáveis 13 C e 15 N são marcadores que permitem a avaliação do panorama pedobioclimático sobre aspectos de mudança vegetacional (metabolismo de plantas), de poluição ambiental e ciclos biogeoquímicos, especialmente os ciclos do C e do N. Este trabalho teve como objetivos estudar os isótopos estáveis de carbono (13 C) e nitrogênio (15 N) e suas relações com atributos químicos (orgânicos e inorgânicos) em 14 solos cultivados com cacau, identificados, avaliados e classificados pelo Sistema Brasileiro de Classificação de Solos. CONCLUSÕES A avaliação dos isótopos em solos cultivados com cacau corrobora com o caráter conservacionista da cacauicultura na região, que manteve um estrato vegetal semelhante ao da floresta nativa, representando um impacto menor no uso racional dos recursos naturais.

RATIONALE: Quantifying the processes that control dissolved inorganic carbon (DIC) dynamics in aquatic systems is
essential for progress in ecosystem carbon budgeting. The development of a methodology that allows high-resolution
temporal data collection over prolonged periods is essential and is described in this study.
METHODS: A novel sampling instrument that sequentially acidifies aliquots of water and utilises gas-permeable ePTFE  tubing to measure the dissolved inorganic carbon (DIC) concentration and d13CDIC values at sub-hourly intervals by Cavity Ring-down spectrometry (CRDS) is described.
RESULTS: The minimum sensitivity of the isotopic, continuous, automated dissolved inorganic carbon analyser (ISOCADICA) system is 0.01 mM with an accuracy of 0.008 mM. The analytical uncertainty in d13CDIC values is proportional to the concentration of DIC in the sample. Where the DIC concentration is greater than 0.3 mM the analytical uncertainty is  0.1 % and below 0.2 mM stability is < _ 0.3 %. The isotopic effects of air temperature, water temperature and CO2 concentrations were found to either be negligible or correctable. Field trials measuring diel variation in d13CDIC values of coral reef associated sea water revealed significant, short-term temporal changes and illustrated the necessity of this technique.
CONCLUSIONS: Currently, collecting and analysing large numbers of samples for d13CDIC measurements is not trivial, but essential for accurate carbon models, particularly on small scales. The ISO-CADICA enables on-site, high-resolution determination of DIC concentration and d13CDIC values with no need for sample storage and laboratory analysis. The initial tests indicate that this system can offer accuracy approaching that of traditional IRMS analysis.

Data for the 13C fraction in atmospheric CO2 from six different measurement stations in the sample period 1977-2014 are studied to estimate its dilution by fossil fuel emissions. No correlation between the annual rate of fossil fuel emissions and annual change in the 13C fraction of atmospheric CO2 is found. We conclude that the 13C data for atmospheric CO2 do not serve as empirical evidence that changes in atmospheric CO2 since the Industrial Revolution can be attributed to fossil fuel emissions 1 .

The abrupt spread of grasslands using C4 photosynthesis, sometimes referred to as the rapid increase in C4 ecosystems (RICE), occurred in the late Miocene in North America. While fossil plant specimens from the Miocene Dove Spring Formation of California as well as data from phylogenetic studies and molecular clocks show that C4 grasses evolved prior to the RICE, most isotopic data from paleosols and mammal tooth enamel suggest that its abundance on the landscape was minimal. However, a few recent studies from the Great Plains suggest that C4 grasslands may have been more prominent prior to the RICE event. Here we examine stable carbon isotope values from ungulate tooth enamel from the Barstow Formation of southern California, which is geographically and temporally close to the Dove Spring Formation, and records a diverse and abundant paleofauna of medial Miocene age. Tooth enamel δ13C values were examined in seven ungulate genera including the hypsodont equids; Acritohippus sp. and Scaphohippus sp.; the camelids, Aepycamelus sp., Hesperocamelus sp., and Procamelus sp.; the antilocaprid, Merycodus sp.; and the proboscidean, Gomphotherium sp. More positive δ13C values observed within the equids, camelids, and antilocaprids are suggestive of C4 grasses being included in the diets of these taxa. The equids exhibited the most positive mean δ13C values, which indicate a higher component of dietary C4 grasses (up to 18%) when compared to the other sampled ungulate taxa. The tooth enamel isotope values presented in this study show the presence of C4 grasses as a significant component of ungulate diets millions of years before the RICE. The abundance of C4 plants earlier in the Miocene may imply a more significant role in the major ungulate diversification events than previously suspected. The few pre-RICE localities showing evidence of C4 abundance suggests that these grasslands were geographically restricted which limits, but may not exclude, the possibility that a world-wide mechanism controlled its spread.

El objetivo general de esta investigación es el análisis de la información de isótopos estables del Carbono y Nitrógeno sobre un conjunto de muestras de restos óseos humanos procedentes de Patagonia meridional continental. El espacio considerado abarca, aproximadamente, desde los 48°30´ S hasta los 54° S, entre los océanos Atlántico y Pacífico y el estrecho de Magallanes. Esta es una escala espacial suprarregional, ya que incluye distintas regiones usualmente consideradas en la bibliografía arqueológica. Nuestro interés principal radica en evaluar la distribución espacial de aquellas muestras que presentan un aporte variable de recursos marítimos en la dieta, razón por la cual tratamos fundamentalmente los rangos de variación dietaria asociados con la ubicación de dichas muestras en el espacio. Esta información nos permitirá discutir aspectos relacionados con los rangos de acción desplegados por las poblaciones humanas. Por otra parte, discutimos dimensiones paleodietarias más específicas con el fin de explorar vías futuras de complejización de nuestras reconstrucciones.

Understanding plant cell wall recalcitrance. Continuous flowthrough pretreatment of 13 C enriched corn stover. Application of time-resolved NMR aided by isotope enrichment. a b s t r a c t This study presents high temperature water-only continuous flowthrough pretreatment coupled with nuclear magnetic resonance (NMR) as a promising analytical tool to examine the plant cell wall, to understand its recalcitrance (i.e., cell wall resistance to deconstruction), and to probe the chemistry occurring during batch pretreatment of biomass. 13 C-enriched corn stover stems were pretreated at 170 °C for 60 min with a hot-water flow rate of 20 mL/min to control fractionation of the cell wall. This approach helped elucidate the nature of plant cell wall chemical recalcitrance and biomass pretreatment chemistry by tracking cell wall fragmentation as a function of time. Fractions of the reactor effluent were collected in a time-resolved fashion and characterized by various NMR techniques to determine the degree and sequence of fragments released, as well as, the chemical composition, molecular structure, and relative molecular weight of those released fragments.

Urine deposition on grassland causes significant N2O losses, which in some cases may result from increased denitrification stimulated by labile compounds released from scorched plant roots. Two 12-day experiments were conducted in 13C-labelled grassland monoliths to investigate the link between N2O production and carbon mineralization following application of low rates of urine-N. Measurements of N2O and CO2 emissions from the monoliths as well as d13C signal of evolved CO2 were done on day)4,)1, 0, 1, 2, 4, 5, 6 and 7 after application of urine corresponding to 3.1 and 5.5 g N m)2 in the first and second experiment, respectively. The d13C signal was also determined for soil organic matter, dissolved organic C and CO2 evolved by microbial respiration. In addition, denitrifying enzyme activity (DEA) and nitrifying enzyme activity (NEA) were measured on day)1, 2 and 7 after the first urine application event. Urine did not affect DEA, whereas NEA was enhanced 2 days after urine application. In the first experiment, urine had no significant effect on the N2O flux, which was generally low ()8 to 14 lg N2ON m)2 h)1). After the second application event, the N2O emission increased significantly to 87 lg N2ON m)2 h)1 and the N2O emission factor for the added urine-N was 0.18%. However, the associated 13 C signal of soil respiration was unaffected by urine. Consequently, the increased N2O emission from the simulated low N-urine patches was not caused by enhanced denitrification stimulated by labile compounds released from scorched plant roots.