Effects of thinning and understory removal on water use efficiency of Pinus massoniana:evidence from photosynthetic capacity and stable carbon isotope analyses

Understanding the relationship between forest management and water use efficiency(WUE)is important for evaluating forest adaptability to climate change.However,the effects of thinning and understory removal on WUE and its key controlling processes are not well understood,which limits our comprehension of the physiological mechanisms of various management practices.In this study,four forest management measures(no thinning:NT;understory removal:UR;light thinning:LT;and heavy thinning:HT)were carried out in Pinus massoniana plantations in a subtropical region of China.Photosynthetic capacity and needle stable carbon isotope composition(δ^(13)C)were measured to assess instantaneous water use efficiency(WUE_(inst))and long-term water use efficiency(WUE_(i)).Multiple regression models and structural equation modelling(SEM)identified the effects of soil properties and physiological performances on WUE_(inst)and WUE_(i).The results show that WUE_(inst)values among the four treatments were insignificant.However,compared with the NT stand(35.8μmol·mol^(-1)),WUE_(i)values significantly increased to 41.7μmol·mol^(-1)in the UR,50.1μmol·mol^(-1)in the LT and 46.6μmol·mol^(-1)in HT treatments,largely explained by photosynthetic capacity and soil water content.Understory removal did not change physiological performance(needle water potential and photosynthetic capacity).Thinning increased the net photosynthetic rate(A_n)but not stomatal conductance(g_s)or predawn needle water potential(ψ_(pd)),implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability.In general,thinning may be an appropriate management measure to promote P.massoniana WUE to cope with seasonal droughts under future extreme climates.

The Response of Carbonate System to Watershed Urbanization Process in a Semi-Arid River

Different from rivers in humid areas,the variability of riverine CO_(2) system in arid areas is heavily impacted by anthropogenic disturbance with the increasing urbanization and water withdrawals.In this study,the water chemistry and the controls of carbonate system in an urbanized river(the Fenhe River)on the semi-arid Loess Plateau were analyzed.The water chemistry of the river water showed that the high dissolved inorganic carbon(DIC)concentration(about 37 mg L^(-1))in the upstream with a karst land type was mainly sourced from carbonate weathering involved by H_(2)CO_(3) and H_(2)SO_(4),resulting in an oversaturated partial pressure of CO_(2)(pCO_(2))(about 800μatm).In comparison,damming resulted in the widespread appearance of non-free flowing river segments,and aquatic photosynthesis dominated the DIC and pCO_(2) spatiality demonstrated by the enriched stable isotope of DIC(δ^(13)CDIC).Especially in the mid-downstream flowing through major cities in warm and low-runoff August,some river segments even acted as an atmospheric CO_(2) sink.The noteworthy is wastewater input leading to a sudden increase in DIC(>55 mg L^(-1))and pCO_(2)(>4500μatm)in the downstream of Taiyuan City,and in cold November the increased DIC even extended to the outlet of the river.Our results highlight the effects of aquatic production induced by damming and urban sewage input on riverine CO_(2) system in semi-arid areas,and reducing sewage discharge may mitigate CO_(2) emission from the rivers.

Processes involving soil CO_(2)dynamic in a sector of Chaco-Pampean plain,Argentina:An isotope geochemical approach

The magnitude and spatial variability of CO_(2)surface emissions and processes involving CO_(2)released to the atmosphere from the soils are relevant issues in the context of climate change.This work evaluated CO_(2)fluxes and^(13)C/^(12)C ratio of vegetation,organic matter,and soil gases from no disturbed soils of Chaco Pampean Plain(Argentina)with different soil properties and environmental conditions(PL and PA units).Soil organic decomposition from individual layers was accompanied byδ^(13)C of total organic carbon(δ^(13)C-TOC)values more enriched to depth.δ^(13)C-TOC values in the upper soil profile~ca.0–15 cm were like the plant community of this area(~−33 to−29‰)whileδ^(13)CTOC varied stronger bellow horizon A,till~−24‰.Bothδ^(13)C-TOC and soilδ^(13)C-CO_(2)were similar(~−24 to 26‰)at deeper horizons(~50–60 cm).Toward the superficial layers,δ^(13)C-TOC andδ^(13)C-CO_(2)showed more differences(till~4‰),due influence of the diffusion process.Horizon A layer(~0–20 cm)from both PL and PA units contained the most enrichedδ^(13)C-CO_(2)values(~−15–17‰)because atmospheric CO_(2)permeated the soil air.A simple two-component mixing model between sources(atmosphericδ^(13)C-CO_(2)and soil CO_(2))confirmed that process.Isotopically,CO_(2)fluxes reflected the biodegradation of C3 plants(source),diffusive transport,and CO_(2)exchange(atmosphere/soil).Soil moisture content appeared as a determining factor in the diffusion process and the magnitude of CO_(2)surface emissions(12–60 g·m^(−2)·d^(−1)).That condition was confirmed by CO_(2)diffusion coefficients estimated by air-filled porosity parameters and soil radon gradient model.

Carbon and Strontium Isotopes of Late Palaeozoic Marine Carbonates in the Upper Yangtze Platform,Southwest China

238 marine carbonate samples were collected from seven sedimentary sections ofthe entire late Palaeozoic (Permian, Carboniferous and Devonian) in the Upper Yangtze Plat-form, southwest China. Based on the absence of cathodoluminescence and very low Mn (gener-ally<50 ppm) contents of the samples, it is thought that they contain information on the orig-inal sea water geochemistry. The results of isotopic analyses of these samples are presented interms of δ^(13)C and ^(87)Sr/^(86)Sr ratios versus geological time. The strontium data, consistent withother similar data based on samples from North America, Europe, Africa and other areas inAsia, support the notion of a global consistency in strontium isotope composition of marinecarbonates. The strontium data exhibit three intervals of relatively low ^(87)Sr/^(86)Sr ratios in thelate Middle Devonian to early Late Devonian, Early Carboniferous and Early Permian, corre-sponding to global eustatic high sea level stands. The lowest ^(87)Sr/^(86)Sr ratio recorded in theLate Permian was probably caused by substantial basalt eruptions in the Upper Yangtze Plat-form at the time. Three corresponding periods of relatively high δ^(13)C values at roughly the samethe intervals were caused by a relatively high rate of accumulation of organic carbon duringsea level rises at these times. The deposition of coal was probably responsible for the increaseof sea water δ^(13)C at other times. The δ^(13)C values drop dramatically near theDevonian/Carboniferous, Carboniferous/Permian and Permian/Triassic boundaries, con-sistent with other similar data, which further support the notion that geological time boundariesare associated with mass extinction and subsequent rejuvenation.

Stable Carbon Isotope Geochemical and Hydrochemical Features in the System of Carbonate-H_2O-CO_2 and Their Implications—Evidence from Several Typical Karst Areas of China

On the basis of hydrochemical observation and experimental calculation, the features of stable carbon isotope geochemistry in the karst dynamic systems of the Guilin Karst Experimental Site, Huanglong Ravine and Wujiangdu Dam Site are summarized in this study. Furthermore, an attempt has been made to solve several geochemical problems, such as the origin of CO2 in the system, kinetic fractionation of carbon isotopes during calcite deposition, hydrochemistry and formation of tufa, and carbon-14 dating of tufa of hydrothermal origin. The results show that three kinds of karst dynamic system can be distinguished: (1) the shallow system, such as the Guilin Karst Experimental Site, in which soil CO2 provides the an active agent for karst processes; (2) the geothermal system, such as the Huanglong Ravine, in which metamorphic or/ and juvenile CO, is the source of activity for karst; (3) the anthropogenic system, such as the Wujiangdu Dam Site, in which the stable carbon isotope geochemical and hydrochemical features have been greatly affected by human activity.

Carbon Isotope Excursions and Paleo-Oceanography of the Ordovician–Silurian Boundary Carbonate Rocks from the Xainza Area, Tibet

Objective The Ordovician–Silurian transitional period is a special time when the global paleo-environment changed greatly.It witnessed the first mass extinction as of Phanerozoic period and glaciations that occurred frequently at a large scale in a very short time,which has thus attracted much attention among geoscientists at home and abroad.

Response to the Lomagundi-Jatuli Event in the southwestern margin of the Yangtze Plate:Evidence from the carbon and oxygen isotopes of the Paleoproterozoic Yongjingshao Formation

The Lomagundi-Jatuli Event(LJE)refers to the significant positive carbon isotope excursion in seawater constituents that occurred immediately after the increase in atmospheric oxygen content during the Paleoproterozoic(2.22-2.06 Ga).Theδ^(13)C values of 46 dolostone samples collected from the Paleoproterozoic Yongjingshao Formation varied in the range of 0.05‰-4.95‰(V-PDB;maximum:4.95‰)in this study,which may be related to the multicellular eukaryotes in the Liangshan Formation in the Yimen Group.They are much higher than theδ^(13)C values of marine carbonates(-1.16‰on average).Theδ^(13)C values of other formations in the Paleoproterozoic Yimen Group are negative.The notable positive carbon isotope anomalies of the Yongjingshao Formation indicate the response to the LJE at the southwestern margin of the Yangtze Block,which is reported for the first time.Furthermore,they are comparable to theδ^(13)C values of carbonates in the Dashiling Formation of the Hutuo Group in the Wutaishan area in the North China Craton,the Wuzhiling Formation of the Songshan Group in the Xiong'er area,Henan Province,and the Dashiqiao Formation of the Liaohe Group in the Guanmenshan area,Liaoning Province.Therefore,it can be further concluded that the LJE is a global event.This study reveals that LJE occurred in Central Yunnan at 2.15-2.10 Ga,lasting for about 50 Ma.The macro-columnar,bean-shaped,and microfilament fossils and reticular ultramicrofossils of multicellular eukaryotes in this period were discovered in the Liangshan Formation of the Yimen Group.They are the direct cause for the LJE and are also the oldest paleontological fossils ever found.The major events successively occurring in the early stage of the Earth include the Great Oxygenation Event(first occurrence),the global Superiortype banded iron formations(BIFs),the Huronian glaciation,the Great Oxygenation Event(second occurrence),the explosion of multicellular eukaryotes,the positive carbon isotope excursion,and the global anoxic and selenium-rich sedimentary event.The authors think that the North China Craton and the Yangtze Craton were possibly in different tectonic locations of the same continental block during the Proterozoic.

Paleoenvironment reconstruction of the Middle Ordovician thick carbonate from western Ordos Basin, China

Reconstructing paleoenvironments has long been considered a vital component for understanding the development and evolution of carbonate reservoirs.The Middle Ordovician Period is considered the archetypical greenhouse interval,and also a critical period in biological evolution.The Middle Darriwilian isotope carbon excursion has been observed in many areas of the world and may be related to the biological explosions caused by decreases in the temperature.The thick carbonate rocks in the fifth member of the Middle Ordovician Majiagou Formation in the Dingbei area of the Ordos Basin were chosen as an example,based on the concentration of major,trace and rare earth elements as well as C,O and Sr isotopic analyses,the paleoenvironment was reconstructed.And its impact on natural gas exploration was analyzed.The results show that the seawater paleotemperature was 29℃,suboxicanoxic paleoredox conditions were observed,and the seawater paleosalinity was high.A large number of plankton in the biological explosion caused a rapid increase in the total organic carbon in carbonate rocks,which provided natural gas as supplemental source rocks.Affected by early meteoric water,the dissolution of gypsum laid the foundation for high-quality reservoirs,and the residual gypsum also further preserved natural gas.This study provides new data for the paleoenvironment and a theoretical basis for further natural gas exploration.

Devonian-Carboniferous Hangenberg Crisis in South China:Variations in Trace Elements,Strontium and Carbon Isotope Chemostratigraphy in the Nanbiancun Carbonate Section

The global Hangenberg Crisis or Hangenberg Extinction is a mass extinction near the Devonian-Carboniferous boundary.Comprehensive research of petrology and geochemistry on the Devonian-Carboniferous boundary,as exposed in the Nanbiancun auxiliary stratotype section,South China,elucidates paleoenvironmental changes and controls on marine strontium(^(87)Sr/^(86)Sr)and carbonate carbon(δ^(13)C_(carb))isotopes during the Hangenberg Crisis.The new^(87)Sr/^(86)Sr data reveal a regression in the Middle Siphonodella praesulcata Zone,while the Hangenberg Extinction was occurring in South China.Moreover,theδ^(13)C_(carb)data records a negative excursion near the base of the Middle Siphonodella praesulcata Zone that may have been connected with the Hangenberg Extinction.A positiveδ^(13)C_(carb)excursion,corresponding with the Upper Siphonodella praesulcata Zone,may reflect the effects of a vigorous biological pump.The magnitude of the Hangenberg Carbon Isotopic Excursion in peakδ^(13)carb values andδ^(13)C_(carb)gradient in carbonate Devonian-Carboniferous boundary sections of the South China Craton during the Hangenberg Crisis,are a function of depositional water depth and distance from the shore.The carbon cycling during the Hangenberg Carbon Isotopic Excursion had a much stronger impact on oceanic surface waters than on the deep ocean and theδ^(13)C_(carb)gradient of local seawater was likely caused by enhanced marine productivity,associated with biological recovery in platform sediments during the Hangenberg Crisis.

Quantitatively unmixing method for complex mixed oil based on its fractions carbon isotopes: A case from the Tarim Basin, NW China

Deep mixed oils with secondary alterations have been widely discovered in the Tarim Basin,but current methods based on biomarkers and isotopes to de-convolute mixed oil cannot calculate the exact mixing proportion of different end-member oils,which has seriously hindered further exploration of deep hydrocarbons in the study area.To solve this problem,we constructed a novel method based on the carbon isotope(δ13C)of the group components to de-convolute mixed liquid hydrocarbons under the material balance principle.The results showed that the mixed oil in the Tazhong Uplift was dominantly contributed at an average proportion of 68% by an oil end-member with heavier d13C that was believed to be generated from the Cambrian-Lower Ordovician source rocks,whereas the mixed oil in the Tabei Uplift was predominantly contributed at an average proportion of 61% by an oil end-member with lighter d13C that was believed to be generated from the Middle-Upper Ordovician source rocks.This indicates that,on the basis of the detailed description of the distribution of effective source rocks,the proposed method will be helpful in realizing differential exploration and further improving the efficiency of deep liquid hydrocarbon exploration in the Tarim Basin.In addition,compared to traditional δ13C methods for whole oil and individual n-alkanes in de-convoluted mixed oil,the proposed method has a wider range of applications,including for mixed oils with variations in color and density,indicating potential for promoting the exploration of deep complex mixed oils in the Tarim Basin and even around the world.

Carbon isotope ratios of n-alkanoic acids: new organic proxies for paleo-productivity in Antarctic ponds

Primary productivity in the Antarctic aquatic environment with simple ecosystems is sensitive to climate and environmental fluctuations.We investigatedδ13C values for n-alkanoic acids derived from phototrophic organisms in a lacustrine sediment core(IIL3)to indicate primary productivity in ponds on Inexpressible Island in the western Ross Sea,Antarctica.Short-chain n-alkanoic acids(C14–C18)were abundant in the IIL3 sediment profile.The carbon isotope ratios of short-chain n-alkanoic acids in the sediment samples and floating microbial mats were similar,indicating that the short-chain n-alkanoic acids in the IIL3 sediment profile predominantly originated from phototrophic organisms.Theδ13C values for the short-chain n-alkanoic acids varied widely through the sediment profile,and 13C-enrichment of n-alkanoic acids was most likely related to high productivity due to carbon-limited conditions caused by enhanced photosynthetic efficiency.Theδ13C values for the n-alkanoic acids changed over the past 3200 years in similar ways to organic proxies for aquatic productivity(n-alkanoic acid and sterol sedimentary fluxes).C16 n-alkanoic acid was enriched in 13C in periods of high aquatic productivity~750–1650 and 3000–3200 a BP but depleted in 13C in periods of relatively low productivity~150–600 and 2500–3000 a BP.The results indicated that carbon isotope ratios of lipids from phototrophic organisms could be used as new proxies to reconstruct paleo-productivity in Antarctic lakes and ponds and therefore improve our understanding of past climate changes.

Rare earth elements(REE)and isotope composition(δ^(13)C andδ^(18)O)of manganese ores of Chiatura deposit(Georgia):features of ore formation and genesis

The rare earth elements(REE)geochemistry and the isotope(δ^(13)C,δ^(18)O)composition of manganese ores of the Chiatura(Georgia)deposit were studied.One of the major features of all types of manganese ores is negative cerium(Ce/Ce*_(PAAS))anomaly and the absence of europium(Eu/Eu*_(PAAS))anomaly.Oxide oolitic manganese ores were formed in oxic shallow marine environments.The content and distribution of REEs(in particular Ce and Eu)in these ores are connected mainly with ferrous oxides.The performed C-and O-isotope research in Mn-carbonates(oolitic and massive)has indicated that carbonate ores were formed by the participation of isotopic ally light CO_(2)which is a result of the oxidation of organic matter in the sediment strata by reducing environments of early diagenesis(and,partially,catagenesis)zone.Obtained negative cerium anomalies in the studied carbonate ores reflect the specific REE patterns in pore waters of sediments of earlier isdiagenesis zone of the Oligocene Chiatura's basin.The deficiency of cerium in this zone remains debatable and requires further study.Formation of manganese carbonates took place multistage by the input of incisional solutions of different chemistry into sea bottom waters and sediments.The absence of europium anomaly indicates about lack of hydrothermal solution input.

Differential response of radial growth and δ^(13)C in Qinghai spruce(Picea crassifolia) to climate change on the southern and northern slopes of the Qilian Mountains in Northwest China

Tree radial growth can have significantly differ-ent responses to climate change depending on the environ-ment.To elucidate the effects of climate on radial growth and stable carbon isotope(δ^(13)C)fractionation of Qing-hai spruce(Picea crassifolia),a widely distributed native conifer in northwestern China in different environments,we developed chronologies for tree-ring widths and δ^(13)C in trees on the southern and northern slopes of the Qilian Mountains,and analysed the relationship between these tree-ring variables and major climatic factors.Tree-ring widths were strongly influenced by climatic factors early in the growing season,and the radial growth in trees on the northern slopes was more sensitive to climate than in trees on the southern.Tree-ring δ^(13)C was more sensitive to climate than radial growth.δ^(13)C fractionation was mainly influenced by summer temperature and precipitation early in the growing season.Stomatal conductance more strongly limited stable carbon isotope fractionation in tree rings than photosynthetic rate did.The response between tree rings and climate in mountains gradually weakened as climate warmed.Changes in radial growth and stable carbon isotope fractionation of P.crassifolia in response to climate in the Qilian Mountains may be further complicated by continued climate change.

Winter-spring minimum temperature variations inferred from tree-ring δ^(13)C in southeastern China

Long-term temperature variations inferred from high-resolution proxies provide an important context to evaluate the intensity of current warming.However,tem-perature reconstructions in humid southeastern China are scarce and particularly lack long-term data,limiting us to obtain a complete picture of regional temperature evolution.In this study,we present a well-verified reconstruction of winter-spring(January–April)minimum temperatures over southeastern China based on stable carbon isotopic(δ^(13)C)records of tree rings from Taxus wallichiana var.mairei from 1860 to 2014.This reconstruction accounted for 56.4%of the total observed variance.Cold periods occurred during the 1860s–1910s and 1960s–1970s.Although temperatures have had an upward trend since the 1920s,most of the cold extremes were in recent decades.The El Niño-Southern Oscillation(ENSO)variance acted as a key modulator of regional winter-spring minimum temperature variability.However,teleconnections between them were a nonlinear process,i.e.,a reduced or enhanced ENSO variance may result in a weakened or intensified temperature-ENSO relationship.

The organic geochemistry of crude oil in the Saltpond Basin(Ghana):Organic source input,depositional environment,and thermal maturity

The Saltpond Basin,situated within the South Atlantic margin of Ghana,is a significant area for petro-leum exploration but has received relatively limited research attention.Previous studies have examined source rock com-position,but data on crude oil organic chemistry are lack-ing,hindering understanding of the basin’s petroleum system and evolution.To address this gap,we analyzed biomarkers and stable carbon-isotope ratios in Saltpond Basin crude oil using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry to eluci-date organic matter source,depositional environment,and thermal maturity.Findings were compared with oils from the West African segment of the South Atlantic margin,namely the Tano Basin and the Niger Delta Basin,to iden-tify potential correlations and gain insights into regional variations.Molecular and isotopic results unveiled a sig-nificant prevalence of organic matter derived from lower marine organisms.Patterns of organic matter deposition and preservation in Saltpond oil samples suggested a suboxic marine transitional environment,contradicting conventional understanding of terrestrial dominance in such settings.Moreover,the potential for degradation processes to obscure differentiation between terrestrial and marine organic mat-ter origins underscores the complex nature of organic mat-ter dynamics in transitional marine environments.Analysis of molecular thermal maturity indices suggested Saltpond oils were expelled from source rocks exhibiting thermal maturity at the early maturity stage.Correlation analysis unveiled genetic disparities among crude oils sourced from the Saltpond Basin and those from the Tano and Niger Delta Basin,primarily due to variations in source input and depo-sitional environment conditions.Saltpond oil exhibits lower terrestrial organic input than Tano Basin’s crude oils,which also have less terrestrial input than Niger Delta Basin crude oils.Additionally,its paleodepositional environment nota-bly differs from oils in the Tano Basin(anoxic transitional marine-lacustrine settings)and the Niger Delta Basin(sub-oxic–oxic terrigenous deltaic or marine or lacustrine envi-ronments).Thermal maturity range of Saltpond oil is com-parable to oils in the Tano Basin but lower than oils in the Niger Delta Basin.Thesefindings provide valuable insights into petroleum generation history and unique organic geo-chemical characteristics within the Saltpond Basin,essen-tial for exploration,production,and environmental manage-ment efforts in the region.Furthermore,correlation studies provide evidence that distinct biological,geological,and paleoenvironmental conditions shaped various oil types in the West African segment of the South Atlantic margin.

Characteristics of carbon isotopic composition of alkane gas in large gas fields in China

Exploration and development of large gas fields is an important way for a country to rapidly develop its natural gas industry.From 1991 to 2020,China discovered 68 new large gas fields,boosting its annual gas output to 1925×108m3in 2020,making it the fourth largest gas-producing country in the world.Based on 1696 molecular components and carbon isotopic composition data of alkane gas in 70 large gas fields in China,the characteristics of carbon isotopic composition of alkane gas in large gas fields in China were obtained.The lightest and average values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become heavier with increasing carbon number,while the heaviest values ofδ^(13)C_(1),δ13C2,δ13C3andδ13C4become lighter with increasing carbon number.Theδ^(13)C_(1)values of large gas fields in China range from-71.2‰to-11.4‰(specifically,from-71.2‰to-56.4‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-18.9‰for coal-derived gas,and from-35.6‰to-11.4‰for abiogenic gas).Based on these data,theδ^(13)C_(1)chart of large gas fields in China was plotted.Moreover,theδ^(13)C_(1)values of natural gas in China range from-107.1‰to-8.9‰,specifically,from-1071%o to-55.1‰for bacterial gas,from-54.4‰to-21.6‰for oil-related gas,from-49.3‰to-13.3‰for coal-derived gas,and from-36.2‰to-8.9‰for abiogenic gas.Based on these data,theδ^(13)C_(1)chart of natural gas in China was plotted.

Geochemical characteristics and origins of natural gases in the eastern Cote d’Ivoire Basin,West Africa

The gas sources in the eastern Cote d’Ivoire Basin(Tano Basin)are seldom reported and remain controversial due to multiple sets of potential source rocks and poorly documented geochemical characteristics of natural gases.The marine source rock potential from the Upper Albian to Turonian as well as the molecular composition and the stable carbon isotope composition of natural gases in the eastern Cote d’Ivoire Basin were studied in detail to investigate the origins of natural gases.The total organic carbon(TOC),hydrogen index(HI),and generation potential(S_(1)+S_(2))of source rocks indicate that both sapropelic source rocks and humic source rocks developed during the late Albian,whereas sapropelic source rocks developed during the Cenomanian and the Turonian.The normal order ofδ^(13)CH_(4)<δ^(13)C_(2)H6<δ^(13)C_(3)H_(8)(δ^(13)C_(1)<δ^(13)C_(2)<δ^(13)C_(3)),the relationship between C_(2)/C_(3)molar ratio andδ^(13)C_(2)-δ^(13)C_(3),and the plot ofδ^(13)C_(1)versus C_(1)/(C_(2)+C_(3))collectively show that the natural gases are thermogenic due to the primary cracking of kerogen,including the typical oil-associated gases from Well D-1,the mixed oil-associated gases and coal-derived gases from Well G-1 and Well L-1.Based on the plot ofδ^(13)C_(1)versusδ^(13)C_(2)and the established relationship betweenδ^(13)C_(1)and equivalent vitrinite reflectance(Ro),we proposed that the natural gases are in a mature stage(Ro generally varies from 1.0%to 1.3%).Combined with results of basin modelling and oil-to-source correlation,the transitional to marine source rocks during the late Albian were thought to have made a great contribution to the natural gases.Our study will make a better understanding on petroleum system in the eastern Cote d’Ivoire Basin.

Changes in the Activities of C4 Pathway Enzymes and Stable Carbon Isotope Discrimination in Flag Leaves of Super High-yield Hybrid Rice

Activities of several key enzymes of C-4 photosynthesis pathway and stable carbon isotope discrimination were investigated in flag leaves of a super high-yield hybrid rice (Oryza sativa L.) cv. Peiai 64S/E32 and a traditional hybrid rice cv. Shanyou 63 at different developing stages. Results show that the activity of PEP carboxylase (PEPCase) increased with age of flag leave; the activity of NADP-malate dehydrogenase (NADP-MDH) increased and reached to a peak value at grain filling stage (68-75 d after transplanting), then fell down; the activity of NADP-MDH in cv. Peiai 64S/E32 was much higher than that in cv. Shanyou 63. Before ripening stage (95 d after transplanting), NADP-malic enzyme activity rose gradually. The level of stable carbon isotope discrimination (Delta(13)C) in flag leaves and grains at different developing stages were similar and exhibited a comparative high value at ripening stage. The average Delta(13)C in leaf of cv. Peiai 64S/E32 during different developing stages was 0.43parts per thousand more than that in cv. Shanyou 63.

Bicarbonate Daily Variations in a Karst River:the Carbon Sink Effect of Subaquatic Vegetation Photosynthesis

Using the Guancun River, an underground stream-fed river, in Rong＇an County of Guangxi, China as a case study, the daily biochemical cycle was examined in this paper based on the data collected a weeklong via high resolution data logger monitoring and high-frequency sampling. Furthermore, the loss of inorganic carbon along its flow path was estimated. Results show that chemical components of the groundwater input are quite stable, showing little change extent; while all of the chemical parameters from two downstream monitoring stations show diel variation over the monitoring period, suggesting that plant activity in the river has a strong influence on water chemistry of the river. The comparison of the input fluxes from the groundwater with the output fluxes of HCO~ estimated at the downstream monitoring station during the high-frequency sampling period shows a strong decrease of HCO~, indicating that the river is losing inorganic carbon along its flow path. The loss is estimated to be about 1,152 mmol/day/m of HCO~ which represent about 94.9 kg/day of inorganic carbon along the 1,350 m section of the Guancun River. It means that HCO~ entering the river from karst underground stream was either consumed by plants or trapped in the authigenic calcite and thus constitutes a natural sink of carbon for the Guancun karst system.

Carbon isotopes of graphite:Implications on fluid history

Stable carbon isotope geochemistry provides important information for the recognition of funda- mental isotope exchange processes related to the movement of carbon in the lithosphere and permits the elab- oration of models for the global carbon cycle. Carbon isotope ratios in fluid-deposited graphite are powerful tools for unravelling the ultimate origin of carbon （organic matter, mantle, or carbonates） and help to constrain the fluid history and the mechanisms involved in graphite deposition. Graphite precipitation in fluid-deposited occurrences results from C02- and/or CH4-bearing aqueous fluids. Fluid flow can be considered as both a closed （without replenishment of the fluid） or an open system （with renewal of the fluid by successive fluid batches）. In closed systems, carbon isotope systematics in graphite is mainly governed by Rayleigh precipi- tation and/or by changes in temperature affecting the fractionation factor between fluid and graphite. Such processes result in zoned graphite crystals or in successive graphite generations showing, in both cases, isotopic variation towards progressive 13C or 12C enrichment （depending upon the dominant carbon phase in the fluid, C02 or CH4, respectively）. In open systems, in which carbon is episodically introduced along the fracture systems, the carbon systematics is more complex and individual graphite crystals may display oscillatory zoning because of Rayleigh precipitation or heterogeneous variations of 613C values when mixing of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation.