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.

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.

Temporal and spatial variations of carbon isotope signature reveal substantial contribution of bracts and internode assimilates to grain filling of japonica rice

Carbon isotope composition(δ^(13)C)of a plant organ is an inherent signature reflecting its physiological property,and thus is used as an integrative index in crop breeding.It is also a non-intrusive method for quantifying the relative contribution of different source organs to grain filling in cereals.Using the samples collected from two-year field and pot experiments with two nitrogen(N)fertilization treatments,we investigated the temporal and spatial variations of δ^(13)C in source organs of leaf,sheath,internode,and bracts,and in sink organ grain.Constitutive nature of δ^(13)C was uncovered,with an order of leaf(−27.84‰)<grain(−27.82‰)<sheath(−27.24‰)<bracts(−26.81‰)<internode(−25.67‰).For different positions of individual organs within the plant,δ^(13)C of the leaf and sheath presented a diminishing trend from the top(flag leaf and its sheath)to the bottom(the last leaf in reverse order and its sheath).No obvious pattern was found for the internode.For temporal variations, δ^(13)C of the leaf and sheath had a peak(the most negative)at 10 days after anthesis(DAA),whereas that of the bracts showed a marked increase at the time point of anthesis,implying a transformation from sink to source organ.By comparing the δ^(13)C in its natural abundance in the water-soluble fractions of the sheath,internode,and bracts with the δ^(13)C in mature grains,the relative contribution of these organs to grain filling was assessed.With reference to the leaf,the internode accounted for as high as 32.64%and 42.56%at 10 DAA and 20 DAA,respectively.Meanwhile,bracts presented a larger contribution than the internode,with superior bracts being higher than inferior bracts.In addition,N topdressing reduced the contribution of the internode and bracts.Our findings clearly proved the actual significance of non-foliar organs of the internode and bracts for rice yield formation,thus extending our basic knowledge of source and sink relations.

Influencing factors and partitioning methods of carbonate contribution to CO_(2)emissions from calcareous soils

In calcareous soils,recent studies have shown that soil-derived CO_(2)originates from both soil organic carbon(SOC)decomposition and soil inorganic carbon(SIC)dissolution,a fact often ignored in earlier studies.This may lead to overestimation of the CO_(2)emissions from SOC decomposition.In calcareous soils,there is a chemical balance between precipitation and dissolution of CaCO_(3)-CO_(2)-HCO_(3),which is affected by soil environmental factors(moisture,temperature,pH and depth),root growth(rhizosphere effect)and agricultural measures(organic materials input,nitrogen fertilization and straw removal).In this paper,we first introduced the contribution of SIC dissolution to CO_(2)emissions from calcareous soils and their driving factors.Second,we reviewed the methods to distinguish two CO_(2)sources released from calcareous soils and quantify the 13C fractionation coefficient between SIC and SIC-derived CO_(2)and between SOC and SOC-derived CO_(2),and to partition three CO_(2)sources released from soils with plants and organic materials input.Finally,we proposed methods for accurately distinguishing three CO_(2)sources released from calcareous soils.This review helps to improve the accuracy of soil C balance assessment in calcareous soils,and also proposes the direction of further investigations on SIC-derived CO_(2)emissions responses to abiotic factors and agricultural measures.

Biochar application significantly increases soil organic carbon under conservation tillage:an 11-year field experiment

Biochar application and conservation tillage are significant for long-term organic carbon(OC)sequestration in soil and enhancing crop yields,however,their effects on native soil organic carbon(native SOC)without biochar carbon sequestration in situ remain largely unknown.Here,an 11-year field experiment was carried out to examine different biochar application rates(0,30,60,and 90 Mg ha^(−1))on native SOC pools(native labile SOC pool I and II,and native recalcitrant SOC)and microbial activities in calcareous soil across an entire winter wheat-maize rotation.The proportions of C_(3) and C_(4)-derived native SOC mineralization were quantified using soil basal respiration(SBR)combined with 13C natural isotope abundance measurements.The results showed that 39-51%of the biochar remained in the top 30 cm after 11 years.Biochar application rates significantly increased native SOC and native recalcitrant SOC contents but decreased the proportion of native labile SOC[native labile SOC pool I and II,dissolved organic carbon(DOC),and microbial biomass carbon(MBC)].Biochar application tended to increase the indicators of microbial activities associated with SOC degradation,such as SBR,fluorescein diacetate hydrolysis activity,and metabolic quotient(qCO_(2)).Meanwhile,higher biochar application rates(B60 and B90)significantly increased the C_(4)-derived CO_(2) proportion of the SBR and enhanced C_(4)-derived native SOC mineralization.The effect of the biochar application rate on the content and proportion of native SOC fractions occurred in the 0-15 cm layer,however,there were no significant differences at 15-30 cm.Soil depth also significantly increased native labile SOC pool Ⅰ and Ⅱ contents and decreased qCO_(2).In conclusion,the biochar application rate significantly increased native SOC accumulation in calcareous soil by enhancing the proportion of native recalcitrant SOC,and biochar application and soil depth collectively influenced the seasonal turnover of native SOC fractions,which has important implications for long-term agricultural soil organic carbon sequestration.

干旱胁迫对甘肃地区5种经济林苗木水分利用效率的影响

干旱作为全球最为常见的自然灾害之一,对农林业生产造成了严重的影响。而在干旱地区影响林木成活率的关键因素之一是植物对水分的利用效率的高低。以核桃、枣、枸杞、沙棘和花椒5个甘肃地区的经济林2年生实生苗木为试材,通过盆栽实验,对其在干旱胁迫(对照、轻度胁迫、中度胁迫和重度胁迫)下的光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、瞬时水分利用效率(WUE_I)、长期水分利用效率(WUE_L)、生物量以及稳定性碳同位素比率(δ^(13)C)等进行了测定,分析了5种苗木δ^(13)C与长期水分利用效率WUE_L之间的关系。结果表明:干旱胁迫处理下,5个经济林树种的Pn、Tr、Gs在中度和重度胁迫与对照间差异显著(P<0.05),而WUE_I则仅花椒、枣和枸杞在重度胁迫与对照间差异显著(P<0.05)。沙棘因较低的Tr而获得了比其它4个树种高的WUE_I。5个经济林苗木的WUE_L和δ^(13)C在重度胁迫与对照间差异显著(P<0.05),而生物量则仅花椒、核桃和枣在重度胁迫与对照间差异显著(P<0.05)。分析发现,枸杞和沙棘δ^(13)C与WUE_L的相关性较其它3个树种高,而枸杞和沙棘在干旱胁迫下的WUE_L也高于其它3个树种,说明干旱条件下高δ^(13)C是评定经济林高WUE的可靠指标。因此,在甘肃地区进行经济林选择时,枸杞和沙棘可在干旱地区种植,而在水分条件较好的地区则可选择其它3个树种。

河西走廊芦苇的光合碳同化途径对生境条件的适应

本文以甘肃省河西走廊生长的四个不同生境芦苇为对象,比较研究了它们的叶解剖结构、光合关键酶活力、乙醇酸氧化酶活力和稳定碳同位素组成(δ^(13)C)。结果发现,沼泽芦苇叶中虽具有不典型的花环结构.但维管束鞘细胞中不含叶绿体,RUBPcase活力/PEPcase活力比值为24.4,乙醇酸氧化酶活力为1218Unitmgpro^(-1)·min^(1δ13)C值为-34‰,这些测值位于C_3植物(小麦)的范围内。生长于沙丘上的芦苇叶片具有明显的花环结构,维管束鞘细胞内含异型叶绿体,RUBPcase活力/PEPcase活力比值为0.985,乙醇酸氧化酶活力为504Unitmgpro^(-1)·min^(-1),δ^(13)C值为-20.9‰,这些测值与典型C_4植物(玉米)十分相似。盐化草甸芦苇和盐化草—沙丘过渡地带芦苇叶中均具有明显的花环结构,维管束鞘细胞中含大型叶绿体。RUBPcase活力/PEPcase活力比值分别为2.45和1.53,但乙醇酸氧化酶活力分别为1470和2058Unitmgpro^(-1)·min^(-1),δ^(13)C值分别为35.6和30.6%,综合盐化草甸芦苇和过渡地带芦苇的上述指标,似介于沼泽芦苇和沙丘芦苇之间。由这些结果可以认为,分布于甘肃省河西走廊的芦苇,在种内发生有由环境因子引起的光合碳代谢途径的适应性改变。

Holocene climate change in the Central Tibetan Plateau inferred by lacustrine sediment geochemical records

Multi-proxies of lacustrine sediments, such as total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), total sulfur (TS), hydrogen index (HI), oxygen index (OI) and stable carbon isotopic composition of organic matter (δ^(13)C_(org)), were analyzed using a 7.3 m core from Zige Tangco. The source of the organic matter in the sediment was mainly from autochthonous phyto-plankton, therefore the significances of proxies can be interpreted as that high TOC, TOC/TS, HI and δ^(13)C_(org) values, low TC, TIC values corresponded to warm and wet climatic condition, and vice versa. The process of climatic development in the Zige Tangco region was hence recovered. During the early and Mid-Holocene, the climate was warm and wet and intensive cold events occurred during the periods of 8600 to 8400 cal a BP and 7400 to 7000 cal a BP. In the second half of Holocene, the climate became cold and dry gradually. The palaeoclimatic process during Holocene in Zige Tangco region matched well with that in Co Ngoin region which is ca 40 km to the south-east. Therefore this palaeoclimatic process represents the Holocene climatic feature in the Central Tibetan Plateau which has the same pattern in the Northern Tibetan Plateau, but the time and duration of some climatic events might be different. We can conclude that in Holocene solar insolation controlled the climatic pattern on the central Tibetan Plateau.

青藏高原达则错沉积物有机碳同位素特征及古气候环境意义

通过对达则错沉积岩心有机质碳同位素(δ^(13)C)和碳氮比(C/N)的分析,结合岩心浮游生物记录、营养盐记录以及温度和降水记录,探讨了过去一千年达则错沉积物有机质δ^(13)C的气候环境指示意义.结果表明,达则错沉积物有机质主要以湖泊自生的水生生物碎屑混合物为主;过去一千年,达则错在受人类活动显著影响之前,气候变化是影响沉积物有机质δ^(13)C形成的主要因素,在1050~1200 AD和1450~1650 AD气候寒冷干燥时段有机质δ^(13)C值显著偏重,反之则相反;过去150年,湖泊沉积物有机质δ^(13)C显著偏重,主要受人类活动导致湖泊营养盐浓度变化影响.本研究还表明对于营养结构较为单一,且西藏拟溞为绝对优势动物物种的半对流型湖泊,应用C/N值判断湖泊有机质来源是不可靠的,需要综合湖泊地理背景谨慎判断.