Long-term biogeochemical cycling in agroecosystems inferred from C, C and N

We investigated C and N cycling in long-term agroecological experiments initiated over 50 years ago at a cool, semi-arid site on the North American Great Plains. We used isotopes at natural abundance to trace C and N exchange between soils and plants in contrasting cropping systems. Both ¹³C and ¹⁴C indicated that the soil organic matter was isotopically distinct from current plant inputs, suggesting that recently added plant C was cycling independently of much of the soil C pool. For tracing recent C flows, bomb-¹⁴C was more sensitive than ¹³C, and increased more in high – than in low – yielding systems. Analysis of ¹⁵N in plant tissues, as an index of ¹⁵N in actively cycling soil N, suggested that biological and industrial N fixation both tended to decrease plant ¹⁵N, whereas livestock manure addition increased ¹⁵N abundance. Collectively, the data suggest that soil organic matter is kinetically heterogeneous, so that a majority of soil C and N inputs and outputs exchange with only the small pool of soil organic matter that is actively cycling. Consequently, recently photosynthesized C and deposited N may not readily enter the old, stable fractions of soil organic matter. Practices to retain CO₂ from the atmosphere and prevent leakage of reactive N to non-agricultural systems should therefore focus on management of this active pool.     

Growth pattern and 13C12C isotope fractionation of Cyanidium caldarium and hot spring algal mats

A study was undertaken with the thermophilic green alga Cyanidium caldarium which grows optimally at low pH and high concentrations of CO₂. Carbon-isotope fractionation was not found to be a simple linear function of temperature. Maximum enrichment of ¹²C in cellular material occurred under optimum growth conditions (at approximately pH 2 and at temperatures between 40–50°C in a CO₂ atmosphere). A maximum measured fractionation of ?24‰ may account for low values ($\text{δ}{}^{13}\text{C}\text{< ?30‰}{}_{\mathrm{<mtext>PDB</mtext>}}$) in Precambrian kerogen presumably derived from algal mats.     

Assessment of MTBE biodegradation in contaminated groundwater using C and C analysis: Field and laboratory microcosm studies

Radiolabelled assays and compound-specific stable isotope analysis (CSIA) were used to assess methyl tert-butyl ether (MTBE) biodegradation in an unleaded fuel plume in a UK chalk aquifer, both in the field and in laboratory microcosm experiments. The ¹⁴C-MTBE radiorespirometry studies demonstrated widespread potential for aerobic and anaerobic MTBE biodegradation in the aquifer. However, δ¹³C compositions of MTBE in groundwater samples from the plume showed no significant ¹³C enrichment that would indicate MTBE biodegradation at the field scale. Carbon isotope enrichment during MTBE biodegradation was assessed in the microcosms when dissolved O₂ was not limiting, compared with low in situ concentrations (2 mg/L) in the aquifer, and in the absence of O₂. The microcosm experiments showed ubiquitous potential for aerobic MTBE biodegradation in the aquifer within hundreds of days. Aerobic MTBE biodegradation in the microcosms produced an enrichment of 7‰ in the MTBE δ¹³C composition and an isotope enrichment factor (ε) of −1.53‰ when dissolved O₂ was not limiting. However, for the low dissolved O₂ concentration of up to 2 mg/L that characterizes most of the MTBE plume fringe, aerobic MTBE biodegradation produced an enrichment of 0.5-0.7‰, corresponding to an ε value of −0.22‰ to −0.24‰. No anaerobic MTBE biodegradation occurred under these experimental conditions. These results suggest the existence of a complex MTBE-biodegrading community in the aquifer, which may consist of different aerobic species competing for MTBE and dissolved O₂. Under low O₂ conditions, the lower fractionating species have been shown to govern overall MTBE C-isotope fractionation during biodegradation, confirming the results of previous laboratory experiments mixing pure cultures. This implies that significant aerobic MTBE biodegradation could occur under the low dissolved O₂ concentration that typifies the reactive fringe zone of MTBE plumes, without producing detectable changes in the MTBE δ¹³C composition. This observed insensitivity of C isotope enrichment to MTBE biodegradation could lead to significant underestimation of aerobic MTBE biodegradation at field scale, with an unnecessarily pessimistic performance assessment for natural attenuation. Site-specific C isotope enrichment factors are, therefore, required to reliably quantify MTBE biodegradation, which may limit CSIA as a tool for the in situ assessment of MTBE biodegradation in groundwater using only C isotopes.     

13C12C exchange between calcite and graphite: A possible thermometer in Grenville marbles

The fractionation of ¹³C between calcite and graphite, Δ(Cc-Gr). is consistently small (2.6–4.8 permil) in 34 assemblages from upper amphibolite- and granulite-facies marbles of the Grenville Province. In 25 samples from the Adirondack Mountains, New York, it decreases regularly with increasing metamorphic temperature. The fractionations are independent of absolute δ¹³C values of calcite (?2.9 to +5.0). For T = 600–800°C, the Adirondack data are described by Δ(Cc-Gr) = ?0.00748T (°C) + 8.68. This good correlation between Δ and T suggests that carbon isotope equilibrium was attained in these high-grade marbles and that the theoretical calculations of this fractionation by Bottinga are approximately 2 permil too large in this temperature range. Because of the relatively high temperature sensitivity suggested by these results and by Bottinga's calculations, and the pressure independence of isotope fractionation, Δ(Cc-Gr) may provide a very good thermometer for high-grade marbles.Comparison of this field calibration for Δ(Cc-Gr) vs temperature with results from other terranes supports the utility of Δ(Cc-Gr) for geothermometry and suggests that graphite is much more sluggish to exchange than calcite, that exchange between calcite and graphite occurs at temperatures as low as 300°C, and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500–600°C.Because ¹³C exchange is an unavoidable metamorphic process at temperatures above 300°C, high values of δ¹³C(Gr) in moderate- to high-grade carbonate-bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite.     

石油和沉积有机质中C3-、C4-烷基取代二苯并噻吩的鉴定

采用人工合成标准物质共注实验、与文献报道的保留指数对比并结合异构体的结构及性质的方法,对石油和沉积有机质中 C3-和 C4-烷基取代二苯并噻吩类含硫多环芳烃化合物进行了系统的鉴定。确定了常规色谱质谱（GC-MS）分析中,烷基取代二苯并噻吩异构体在 HP-5MS （5%-苯基甲基聚硅氧烷）色谱柱上的标准保留指数。确认了前人初步鉴定的部分三甲基二苯并噻吩异构体甲基取代基位置,初步比较了 C3-和 C4-烷基取代二苯并噻吩在不同成因石油和沉积有机质中的分布特征,初步探讨了 C3-和 C4-烷基取代二苯并噻吩潜在的地球化学意义。研究结果为今后进一步探索烷基取代二苯并噻吩系列在石油和沉积有机质中的地球化学意义奠定了可靠的基础。     

C3 and C4 Biomass Allocation Responses to Elevated CO2 and Nitrogen: Contrasting Resource Capture Strategies

Plants alter biomass allocation to optimize resource capture. Plant strategy for resource capture may have important implications in intertidal marshes, where soil nitrogen (N) levels and atmospheric carbon dioxide (CO₂) are changing. We conducted a factorial manipulation of atmospheric CO₂ (ambient and ambient?+?340?ppm) and soil N (ambient and ambient?+?25?g?m^?2?year^?1) in an intertidal marsh composed of common North Atlantic C₃ and C₄ species. Estimation of C₃ stem turnover was used to adjust aboveground C₃ productivity, and fine root productivity was partitioned into C₃?CC₄ functional groups by isotopic analysis. The results suggest that the plants follow resource capture theory. The C₃ species increased aboveground productivity under the added N and elevated CO₂ treatment (P?<?0.0001), but did not under either added N or elevated CO₂ alone. C₃ fine root production decreased with added N (P?<?0.0001), but fine roots increased under elevated CO₂ (P?=?0.0481). The C₄ species increased growth under high N availability both above- and belowground, but that stimulation was diminished under elevated CO₂. The results suggest that the marsh vegetation allocates biomass according to resource capture at the individual plant level rather than for optimal ecosystem viability in regards to biomass influence over the processes that maintain soil surface elevation in equilibrium with sea level.     

n-Alkane distribution and carbon stable isotope composition in leaf waxes of C3 and C4 plants from Angola

Palaeoenvironmental assessment of past C₃ and C₄ vegetation distributions relies on end member data from plant analyses. In southwestern Africa, end member data of the carbon number distribution of n-alkanes from leaf waxes and their carbon isotopic composition were available for the rainforest and the savannah. To complement this, we analysed the n-alkane parameters of 41 C₃ plants and 11 C₄ plants from the transition region, i.e., the wood- and shrubland of Angola. The combined results for the rainforest, the wood- and shrubland and the savannah show an increase in the average chain length (ACL) of C₃ and C₄ plants and an increasingly enriched carbon stable isotope composition for the C₃ plants from the equator towards southern Africa. The enlarged database was applied to the data of a north–south transect of deep-sea surface sediments already used in a previous study, which resulted in the proxies showing a good reflection of the vegetation on the adjacent southwest African continent in terms of %C₄ plant cover. Applying end member values for ACL and δ¹³C obtained from the enlarged database by two different averaging methods (arithmetic average and median) to the n-alkane data from the sediment transect yielded similar vegetation reconstructions. In addition, a correlation between ACL and growth height of the plants is discussed, indicating that the ACL may be useful as a tree abundance parameter. Thus, the enlarged end member database strengthens the n-alkane parameters as tools for palaeoenvironmental studies.     

Carbon isotope and C/N ratios of suspended matter in rivers: an indicator of seasonal change in C4/C3 vegetation

A combination of δ ¹³C values with C/N ratios in suspended matter has been used to examine the seasonal relationship between C₄ and C₃ vegetation along the Loess Plateau, NW China. The C isotopic composition of suspended organic matter in rivers, together with C/N ratios can differentiate between soil and plant material, and can be used to estimate the relative contributions of soil organic C and plant litter to the suspended matter. The relationship between C isotopic composition and C/N ratios indicates that the samples are a mixture of two end members: (1) modern soils with relatively constant δ ¹³C values, low C content and low C/N ratios; (2) plant litter with varying δ ¹³C values, high C content and high C/N ratios. The results reflect the seasonal distribution of C₄/C₃ vegetation within the area studied, as part of the Loess Plateau. The abundance of C₄ grasses is about 20% for the current summer vegetation ecosystem in the eastern part of the Loess Plateau. Hence, the use of δ ¹³C values and C/N ratios of suspended matter in rivers and modern soil may be useful for reflecting seasonal distribution of C₄/C₃ vegetation in catchments. This could be a useful tool for distinguishing between catchments for GIS studies, and long term planning for ecological management of catchment areas.     

The occurrence and identification of C30, C31 and C32 alkan-1, 15-diols and alkan-15-one-1-ols in Unit I and Unit II Black Sea sediments

Two limited series of alkan-1, 15-diols and alkan-15-one-1-ols with chain lengths of 30, 31 and 32 carbon atoms have been isolated from extracts of Unit I (0–3000 yr BP) and Unit II (3000–7000 yr BP) Black Sea sediments.     

Climatic significance of D/H and13C/12C ratios in Irish oak cellulose

δD and δ¹³C analyses of cellulose nitrate from two modern Irish oak trees that form part of the 7400 year long chronology were carried out, covering a period of 123 years (1861–1983 A.D.) with a 5 year resolution so as to assess the potential of this long chronology for retrieval of palaeoenvironmental data. One of the trees (Q5293) showed significant correlations of δD, δ¹³ C and ring width with mean annual temperatures as recorded at the Armagh weather station nearby and the mean fall temperatures of Central England. The other tree (Q5296) did not exhibit any significant climatic correlations either because it grew utilizing a nearby permanent source of ground water or because the intra-ring isotopic variations in Irish oak are significant enough to mask the climatic signal. Whilst our results have given a positive indication of the usefulness of these trees for palaeoenvironmental information, more trees need to be analysed to confirm our findings. Even though one of the trees did not exhibit climatic correlations, both trees show a significant positive correlation of δ¹³C and a negative correlation of δD with ring width variations. Furthermore, two tree samples that grew during the 1620s B.C., when a volcano is thought to have erupted on the Aegean island of Santorini, show increased δD and decreased δ¹³C for one to two decades following the eruption, though the magnitudes of change seem to vary with site and trees. We have proposed a possible mechanism based on tree phenology to explain both the above effects.     

13C12C ratios of pleistocene mummified remains from beringia

During the Quaternary glacial episodes, when sea level was considerably lower, Asia and North America were linked by large extensions of circumarctic land (Beringia), which remained unglaciated. This land mass served not only as a biogeographical bridge for plants, animals, and humans, but also supported a biome very different from present tundra or boreal coniferous forests, which was dominated by steppes and a rich mammalian megafauna. Carbon stable isotope ratios of Beringian late Pleistocene mummified remains of bison, equids, mammoth, caribou, musk-ox, moose, woolly rhino, and other undetermined species, found preserved in permafrost, indicate that these megaherbivores fed exclusively on C₃ plants, and that C₄ grasses were not differentially ingested by bison, as previously suggested. Paleoclimatic constraints probably prevented the formation of a warm-season (C₄) guild during the later part of the growing season in the steppes of Beringia during the last glaciation.     

The system Ag-Sb-S from 600°C to 200°C

The system Ag-Sb-S was studied between 600°C and 200°C in evacuated silica glass tubes. Results from lower temperature runs require shifts in the stable tie-line configuration found by Barstad at 400°C. It is proposed that the configuration changes near 300°C, and that at 200°C the equilibrium assemblages correspond to those usually reported for minerals in ores. Most of the minerals of the system were synthesized. In addition, the synthetic phase Ag₇SbS₆ (antimony analogue of the arsenic mineral billingsleyite) is characterized, and the ease of its synthesis in the composition area bounded by argentite-pyrargyrite-sulfur suggests the probable existence of a mineral of this composition. The relatively common mineral stephanite (Ag₅SbS₄) was not formed as a synthetic product in the temperature range of this study. Combined DTA and X-ray data show that at 197±5°C stephanite decomposes in the absence of sulfur to form pyrargyrite plus argentite, whereas with excess sulfur the products are Sb-billingsleyite plus pyrargyrite. Pyrostilpnite (Ag₃SbS₃), the low temperature dimorph of pyrargyrite, is unstable above 192±5°C.

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Das ternäre System Silber-Antimon-Schwefel wurde zwischen 600° und 200°C untersucht und versucht, die Gleichgewichtszustände aller stabilen Phasen zu analogen natürlichen Mineralien in Beziehung zu setzen. Neben den Elementen wurden an binären Phasen Allargentum, Dyskrasit, Antimonit, Argentit bzw. Akanthit gefunden oder bestätigt. Auf dem pseudo-binären Schnitt Ag₂S-Sb₂S₃ liegen Pyrargyrit und Miargyrit, während eine als Mineral unbekannte ternäre Phase Ag₇SbS₆ (entsprechend dem natürlichen As-Analogon Billingsleyit) nur bei höherem Schwefelangebot beständig ist. Hier nicht synthetisch dargestellte Silber-Antimon-Sulfosalze liegen vermutlich unterhalb der 200°C-Grenze. So ließ sich mittels Differential-Thermo-Analyse und röntgenographischer Bestimmungsmethoden der inkongruente Zerfall von Stephanit in Argentit und Pyrargyrit bei 197±5°C bestimmen. Pyrostilpnit (Ag₃SbS₃) ist nur unterhalb 192±5°C beständig.

     

RSM-12C多通道瞬态信号记录处理仪性能简介

<正> 继曾在全国发明展览会上展出,曾获黄鹤发明奖的RSM-08多通道瞬态信号记录处理仪之后,中国科学院武汉岩土力学所最近又推出了新的一代仪器,RSM-12C多通道瞬态信号记录处理仪。最近已通过湖北省计量测试所的测试,测试的结果表明该仪器的主要性能指标达到或接近日本80年代产品DM-711D数字波形存贮器的水平。     

Synthetic “Cooperite”, “Braggite”, and “Vysotskite” in the system PtS-PdS-NiS at 1100°C, 1000°C, and 900°C

Summary ?Results of experimental investigations in the dry system PtS-PdS-NiS at 1100°C, 1000°C, and 900°C are presented. The phases observed at 1100°C are “cooperite” and a melt, at 1000°C “cooperite”, “braggite”, and a melt and at 900°C “cooperite”, “braggite”, “vysotskite”, Ni_1−xS, and a melt. At 1100°C the maximum solubility of Ni in ideal, Pd-free “cooperite” is 2.7 atomic per cent and the Pd-content limit in Ni-free “cooperite” is 12.8 atomic per cent. At 1000°C the maximum solubility of Ni in ideal, Pd-free “cooperite” is 3.3 atomic per cent and the Pd-content in Ni-free “cooperite” is 13.7 atomic per cent. The “braggite” composition ranges from Pt_0.56Pd_0.38Ni_0.06S and Pt_0.59Pd_0.41S in a Ni-saturated and Ni-free environment respectively to Pt_0.18Pd_0.80Ni_0.02S and Pt_0.14Pd_0.86S respectively. At 900°C the maximum Ni-content in ideal Pd-free “cooperite” is 3.1 atomic per cent and the Pd-limit in Ni-free “cooperite” is 12.5 atomic per cent. The “braggite” composition ranges from Pt_0.59Pd_0.29Ni_0.12S and Pt_0.60Pd_0.40S for a Ni-saturated and Ni-free environment respectively, to Pd_0.91Ni_0.09S and PdS respectively. The Ni-content in “braggite” and “vysotskite” increases slightly with increasing Pt/Pd ratios and is higher at 900°C than at 1000°C. Comparison of experimental trends with cooperite, braggite, and vysotskite analyses from the literature implies high temperatures of formation for Pt-Pd-Ni sulphides in placers if Ni-saturation is assumed.

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Zusammenfassung ?Synthetischer ,,Cooperit”, ,,Braggit” und “Vysotskit” im System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C Ergebnisse experimenteller Untersuchungen im trockenen System PtS-PdS-NiS bei 1100°C, 1000°C und 900°C werden dargestellt. Bei 1100°C sind die Phasen “Cooperit” und Schmelze, bei 1000°C “Cooperit”, “Braggit” und Schmelze und bei 900°C “Cooperit”, “Braggit”, “Vysotskit”, Ni_1−xS und Schmelze stabil. Bei 1100°C ist die maximale L?slichkeit von Ni in idealem, Pd-freiem “Cooperit” 2.7 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.8 Atomprozent. Bei 1000°C ist die maximale L?slichkeit von Ni in idealem, Pd-freien “Cooperit” 3.3 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 13.7 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt_0.56Pd_0.38Ni_0.06S und Pt_0.18Pd_0.80Ni_0.02S in einem Ni-ges?ttigtem und zwischen Pt_0.59Pd_0.41S und Pt_0.14Pd_0.86S in einem Ni-freien Umfeld. Bei 900°C liegt die maximale L?slichkeit von Ni in idealem Pd-freien “Cooperit” bei 3.1 Atomprozent und der Pd-Gehalt in Ni-freien “Cooperit” liegt bei maximal 12.5 Atomprozent. Die Zusammensetzung des “Braggits” variiert zwischen Pt_0.59Pd_0.29Ni_0.12S und Pd_0.89Ni_0.08S in einem Ni-ges?ttigten und zwischen Pt_0.59Pd_0.40S und PdS in einem Ni-freien Umfeld. Der Nickelgehalt in “Braggit” und “Vysotskit” nimmt mit zunehmendem Pt/Pd Verh?ltnis zu und ist bei 900°C h?her als bei 1000°C. Ein Vergleich der experimentellen Trends mit Cooperit, Braggit und Vysotskit Analysen aus der Literatur weist auf eine Hochtemperaturbildung der Pt-Pd-Ni Sulfide in Seifenlagerst?tten hin, wenn man von Nickels?ttigung ausgeht.

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Received October 1, 1998;/revised version accepted September 7, 1999     

南海沉积物中C30-C32烷基二醇的检出及可能的古环境信息

从南海17962钻孔沉积物中检出了C30－C32长链烷基二醇类化合物。C30长链烷基二醇的碳同位素值在－30．17‰－－38．98‰之间,反映出其先质母体为水生生物,认为是海洋微藻－黄绿藻Eustigmatophytes。这类化合含量能够反映以黄绿藻为代表的海洋古生产力的变化：冰期时C30二醇的高沉积通量显示出南海南部末次冰期黄绿藻Eustigmatophytes初级生产力增高。计算C30和C32二醇的相对比值获得二醇参数（diols indices）,发现本柱状样二醇参数的变化指示了南海3万余年来的古海洋及古气候变化：南海经历了从半封闭到开放的演化,其气候经历了三次Heinrich冷事件,在Heinrich事件之间出现了一系列百年到千年尺度的气候事件,即D／O循环;全新世的Younger Dryas事件也有明显反映,说明南海与高纬度地区3万余年来的气候变化存在遥相关。     

The occurence of unusual C27 and C29 sterane predominances in two types of Oman crude oil

Two types of Oman crude oils reveal unusual sterane distributions. Type “A”, which is the more common (74 examples), is characterised by a predominance of C₂₉ iso- and normal-steranes and generally none or only very low relative concentrations of rearranged-steranes. The triterpanes are characterised by the predominance of the C₂₉ 17αH, 21βH norhopane over the C₃₀ 17αH, 21βH hopane and non-predominant C₂₀–C₃₀ tricyclic terpanes. The C₂₉ steranes of this type of crude were not derived from the C₂₉ sterols of land-plant origin (frequently proposed as the source of C₂₉ steranes) since there is good geological evidence that these crudes were generated from a pre-Cambrian source rock, a geological period when land-plants did not exist.The type “B” crude oil (11 known examples) is characterised by a strong predominance of C₂₇ iso-, normal- and rearranged-steranes, relatively lower concentrations of 17αH, 21βH hopanes and relatively high concentrations of C₂₀–C₃₀ tricyclic terpanes.The remarkably different biomarker characteristics of these crude oils imply that the organisms active in the depositional environment of the respective source rocks were significantly different.     

C/C++与FORTRAN混合编程技术及其应用研究

详细论述了C/C ++和FORTRAN混合编程技术 ,尤其是对动态连接库方法进行了重点介绍。将C/C ++和FORTRAN进行混合编程 ,一方面可以达到这两种语言优势互补的目的 ;另一方面可以再利用前人留下的大量成熟的FORTRAN程序 ,避免了重复编程和资源浪费 ,节约了大量编程时间。