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81.
A number of ancient charred paddies with a 14C dating of about 5900 a BP were recovered in the sixth excavation at Chuodun Site and are assigned to the Majiabang culture
(7–6 ka BP). To understand their formation mechanism, the ancient charred paddies were compared to modern paddies using FT-IR
spectrum and thermaogravimetric analysis. At the same time, modern charred paddies were made in helium by the laboratory method,
and the structural characteristics of them and the ancient ones were revealed using CP/MAS-13C-NMR. Our results show there are more aromatic moieties in ancient charred paddies compared to modern paddies. The aliphatic
components of modern charred paddies decrease continuously, accompanied by the accumulation of aromatic components, when the
duration and temperature of oxidation increase, and the structure buildings of modern charred paddies are more similar to
ancient ones. Given the planting manner of paddies during Majiabang culture period, these ancient charred paddies might be
a result of the original farming mode involving fire.
Supported by the National Natural Science Foundation of China (Grant No. 40571088) 相似文献
82.
荒漠植物叶片碳同位素组成及其水分利用效率 总被引:46,自引:17,他引:29
水分通常是影响荒漠植物生长的主要限制因子,然而当前很少有关于荒漠群落中植物水分利用效率的报道。作为指示水分利用效率的可靠指标,叶片稳定碳同位素组成(δ13 C值)可以用来探讨植物适应干旱环境的强弱程度。对阜康和金塔同种或同属的植物叶片δ13 C的测量结果表明,干旱可使植物叶片δ13 C升高:年降水量每增加1mm,叶片δ13 C则降低001‰~ 0015‰。阜康荒漠灌木叶片δ13 C值明显高于草本,这样的趋势也存在于甘肃金塔主要荒漠植物中,与前人的报道也基本一致。说明灌木可能更适应干旱胁迫,并且这种现象可能是全球荒漠生态系统的一种共性。对阜康四种荒漠代表植物红砂、梭梭、补血草和骆驼刺的SOD活性的测定结果间接地支持了这一结果。进一步的分析表明,藜科、豆科和某些禾本科植物适应干旱环境的能力相对较强。 相似文献
83.
84.
中更新世气候转型时期南海生态环境的南北差异 总被引:2,自引:0,他引:2
中更新世气候转型在南海浮游有孔虫、氧同位素和其它生物记录上主要反映在900 ka BP前后发生高频率变化,特别是指示表层水骤然降温。北部冬季表层水温从24~25℃降至17~28℃,而南部也从26~27℃降至23~24℃。总的降温趋势与开放西太平洋一致,直接反映了西太平洋暖池在900 ka BP之后MIS22期间有明显的减弱。表层水大幅度降温还发生在后继的MIS 20、18、16几大冰期,说明主要冰期旋回周期由41 ka转变为100 ka经历了长达400 ka的过渡时期,并且冬季风增强也在过渡时期的后半段最明显。南海南北生物组合和δ18O值的差异,突出了中更新世气候转型期边缘海区南北气候梯度反差和冬季风在冰期增强的讯号。结论是:生态环境系统反应总体表现与冰期旋回一致的同时,还包含了独特的地区性系统演变特征。但是,南海—西太平洋地区在0.9 Ma BP前后表层海水盐度因东亚冬季风和海平面下降的定量变化,以及这些变化对气候转型时期海—气耦合过程和生态环境系统的影响,尚缺乏足够的资料和证据。 相似文献
85.
86.
为了探究施氮对土壤有机质(SOM)的激发效应,本研究在施氮梯度样地(0、4和16 g N m–2 yr–1)上进行了13C标记葡萄糖的原位添加实验,并对土壤CO_2排放量和磷脂脂肪酸(PLFA)含量进行了测定。研究发现施氮降低了土壤CO_2排放、土壤PLFA含量以及土壤真菌细菌比。在0 g N m–2 yr–1样地上葡萄糖添加导致的正向激发效应最强,同时4 g N m–2 yr–1样地释放的葡萄糖来源的碳最多。因此,施氮减少了土壤中SOM转化产生的CO_2,微生物碳的来源由SOM转变为添加的易分解碳。本研究采样早期土壤微生物生物量和群落结构稳定,表明该草原存在"表观激发效应",因此未来研究应着重对微生物功能的多样性进行探讨。 相似文献
87.
赣江上游河流水化学的影响因素及DIC来源 总被引:20,自引:0,他引:20
对赣江上游38 处水体采样点的水化学特征和溶解无机碳稳定同位素的分析, 发现其总溶解质浓度较低, 其中, 阳离子以Na+、Ca2+ 为主, 阴离子以Cl- 和HCO3 - 为主, Si 的浓度较高, 表征了典型硅酸盐地区河流的水化学组成特征。通过海盐校正分析得出, 研究区大气降水对河水溶解质的贡献率为11.5%, 扣除降水的贡献部分, 利用主成分分析的方法, 计算得出赣南流域受硅酸盐岩风化作用强烈, 同时由于受附近盐矿的影响, 蒸发盐岩的风化作用显著。另外, 根据δ13C 溶解无机碳DIC 的测量值约为-8.35‰~-13.74‰, 平均为-11.65‰, 利用质量平衡计算得出, 研究区DIC 的主要来源, 约68.5%来自于土壤CO2, 31.5%来自于碳酸盐矿物的溶解, 进而得出流域岩石化学风化过程消耗的土壤CO2 为2.11×105 mol/yr·km2, 来自碳酸盐本身的HCO3 -含量为9.6×104 mol/yr·km2。由于地理位置和流域环境以及人为因素的差异, 各支流DIC 来源的比例亦有所差异。 相似文献
88.
Comparison of ecophysiological characteristics between introduced and indigenous mangrove species in China 总被引:2,自引:1,他引:1
Luzhen Chen Nora F.Y. Tam Jianhui Huang Xueqin Zeng Xiangli Meng Cairong Zhong Yuk-shan Wong Guanghui Lin 《Estuarine, Coastal and Shelf Science》2008,79(4):644-652
Due to its rapid growth, the introduced mangrove species Sonneratia apetala from Bangladesh has been widely used in mangrove restoration in southeastern China since 1985. As an indigenous mangrove species in Hainan, China, Sonneratia caseolaris was also planted in Guangdong Province for afforestation purposes. Both species have developed well in their new habitats, but their ecophysiological differences with the native mangrove species have not been studied. In this study, leaf gas exchange, water and nitrogen use efficiencies of two Sonneratia species were compared with those of selected native mangrove species (Avicennia marina, Aegiceras corniculatum, Kandelia candel, and Excoecaria agallocha) in Hainan and Shenzhen. The introduced S. apetala maintained lower carbon assimilation rate (A) and photosynthetic nitrogen use efficiency (PNUE) than the indigenous S. caseolaris. In Shenzhen, the two introduced Sonneratia had comparable photosynthetic rates and water use efficiency (WUE) with the native mangrove species, except that PNUE in S. caseolaris was significantly higher than in the native mangrove species. The two Sonneratia species showed significant overlap in PNUE and long-term WUE. Photosynthetic parameters derived from leaf photosynthetic light–response curves and A–Ci curves also suggested lower carbon assimilation capacities for the introduced Sonneratia than for the native mangrove species in both study sites. The lower light compensation point (LCP) of two introduced Sonneratia in both study sites also indicated a better adaptation to a low light regime than the native mangrove species. The results of photosynthetic capacities indicated that the introduced mangrove species have little competitive advantage over local native mangrove species in their respective new habitats. 相似文献
89.
P.P. Povinec J. de Oliveira E.S. Braga J.-F. Comanducci J. Gastaud M. Groening I. Levy-Palomo U. Morgenstern Z. Top 《Estuarine, Coastal and Shelf Science》2008
Stable isotopes, tritium, radium isotopes, radon, trace elements and nutrients data were collected during two sampling campaigns in the Ubatuba coastal area (south-eastern Brazil) with the aim of investigating submarine groundwater discharge (SGD) in the region. The isotopic composition (δD, δ18O, 3H) of submarine waters was characterised by significant variability and heavy isotope enrichment. The stable isotopes and tritium data showed good separation of groundwater and seawater groups. The contribution of groundwater in submarine waters varied from a few % to 17%. Spatial distribution of 222Rn activity concentration in surface seawater revealed changes between 50 and 200 Bq m−3 which were in opposite relationship with observed salinities. Time series measurements of 222Rn activity concentration in Flamengo Bay (from 1 to 5 kBq m−3), obtained by in situ underwater gamma-spectrometry showed a negative correlation between the 222Rn activity concentration and tide/salinity. This may be caused by sea level changes as tide effects induce variations of hydraulic gradients, which increase 222Rn concentration during lower sea level, and opposite, during high tides where the 222Rn activity concentration is smaller. The estimated SGD fluxes varied during 22–26 November between 8 and 40 cm d−1, with an average value of 21 cm d−1 (the unit is cm3/cm2 per day). The radium isotopes and nutrient data showed scattered distributions with offshore distance and salinity, which implies that in a complex coast with many small bays and islands, the area has been influenced by local currents and groundwater–seawater mixing. SGD in the Ubatuba area is fed by coastal contaminated groundwater and re-circulated seawater (with small admixtures of groundwater), which claims for potential environmental concern with implications on the management of freshwater resources in the region. 相似文献
90.
Andrew J.P. Harwood Paul F. Dennis Alina D. Marca Graham M. Pilling Richard S. Millner 《Estuarine, Coastal and Shelf Science》2008
Based on measurements of the 18O isotope composition of 247 samples collected over a 3-year period we have assessed the oxygen isotope composition of water masses in the North Sea. This is the first δ18O data set that covers the entire North Sea basin. The waters lie on a mixing line: δ18O (‰VSMOW) = −9.300 + 0.274(S) with North Atlantic sub-polar mode water (SPMW) and surface waters, and Baltic Sea water representing the saline and freshwater end members respectively. Patterns exhibited in surface and bottom water δ18O distributions are representative of the general circulation of the North Sea. Oxygen-18 enriched waters from the North Atlantic enter the North Sea between Scotland and Norway and to a lesser extent through the English Channel. In contrast, oxygen-18 depleted waters mainly inflow from the Baltic Sea, the rivers Rhine and Elbe, and to a lesser degree, the Norwegian Fjords and other river sources. Locally the δ18O–salinity relationship will be controlled by the isotopic composition of the freshwater inputs. However, the range of local freshwater compositions around the North Sea basin is too narrow to characterise the relative contributions of individual sources to the overall seawater composition. This dataset provides important information for a number of related disciplines including biogeochemical research and oceanographic studies. 相似文献