lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai （35°N）, the Loess Plateau. Stable carbon isotopic ...lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai （35°N）, the Loess Plateau. Stable carbon isotopic composition indicates that （ ⅰ ） C<sub>4</sub> plants might be present at least by7.0 Ma; （ ⅱ ） C<sub>4</sub> plants expanded gradually between ～4.0 and ～3.2 Ma, and their biomass fraction was up to 50%; and （ ⅲ ） the biomass of C<sub>4</sub> vegetation since ～2.0 Ma seems to have been decreased to the level （about 20%） before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal展开更多
Carbon isotopes of pedogenic carbonate are often used to study paleoenvironments, but the existence of detrital carbonate changes the carbon isotopic composition. To develop an experimental method to determine existen...Carbon isotopes of pedogenic carbonate are often used to study paleoenvironments, but the existence of detrital carbonate changes the carbon isotopic composition. To develop an experimental method to determine existence of detrital carbonate in carbonate nodules, and to avoid it during isotope analysis, 23 pedogenic carbonate nodules in Miocene loess from the Loess Plateau of China were studied through micromorphology and carbon isotope analysis. The difference in carbon isotopic composition between matrix carbonate (B) and pore carbonate (A) (δ 13C(B-A)) ranges from 0.27‰ to 0.44‰ in nodules containing detrital carbonate and -0.16‰ to 0.13‰ in nodules where detrital carbonate is absent. The latter is within measurement error, but the former is beyond it. Here we propose an isotopic approach to determine if nodules contain detrital carbonate: if δ 13C(B-A) is within the measurement error, the nodules do not contain detrital carbonate, and vice versa. We suggest that it is better to analyze pore carbonate instead of matrix carbonate when using carbon isotope of carbonate nodules to reconstruct paleoenvironments.展开更多
Knowledge of soil carbon（C） distribution and its relationship with the environment can improve our understanding of its biogeochemical cycling and help to establish sound regional models of C cycling. However, such ...Knowledge of soil carbon（C） distribution and its relationship with the environment can improve our understanding of its biogeochemical cycling and help to establish sound regional models of C cycling. However, such knowledge is limited in environments with complex landscape configurations. In this study, we investigated the vertical distribution and storage of soil organic carbon（SOC） and soil inorganic carbon（SIC） in the 10 representative landscapes（alpine meadow, subalpine shrub and meadow, mountain grassland, mountain forest, typical steppe, desert steppe, Hexi Corridor oases cropland, Ruoshui River delta desert, Alxa Gobi desert, and sandy desert） with contrasting bioclimatic regimes in the Heihe River Basin, Northwest China. We also measured the 87 Sr/86 Sr ratio in soil carbonate to understand the sources of SIC because the ratio can be used as a proxy in calculating the contribution of pedogenic inorganic carbon（PIC） to total SIC. Our results showed that SOC contents generally decreased with increasing soil depth in all landscapes, while SIC contents exhibited more complicated variations along soil profiles in relation to pedogenic processes and parent materials at the various landscapes. There were significant differences of C stocks in the top meter among different landscapes, with SOC storage ranging from 0.82 kg C/m^2 in sandy desert to 50.48 kg C/m^2 in mountain forest and SIC storage ranging from 0.19 kg C/m^2 in alpine meadow to 21.91 kg C/m^2 in desert steppe. SIC contributed more than 75% of total C pool when SOC storage was lower than 10 kg C/m^2, and the proportion of PIC to SIC was greater than 70% as calculated from Sr isotopic ratio, suggesting the critical role of PIC in the C budget of this region. The considerable variations of SOC and SIC in different landscapes were attributed to different pedogenic environments resulted from contrasting climatic regimes, parent materials and vegetation types. This study provides an evidence for a general trade-off pattern between SOC展开更多
The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,whi...The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,while the development of soil profiles would account for both organic and inorganic carbon burial.As compared with soil organic carbon,inorganic carbon burial,collectively known as the soil carbonate,would have a greater impact on the long-term carbon cycle.Soil carbonate would have multiple carbon sources,including dissolution of host calcareous rocks,dissolved inorganic carbon from freshwater,and oxidation of organic matter,but the host calcareous rock dissolution would not cause atmospheric CO2drawdown.Thus,to evaluate the potential effect of soil carbonate formation on the atmospheric p CO2level,different carbon sources of soil carbonate should be quantitatively differentiated.In this study,we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop,consisting of limestone of the early Paleogene Guanzhuang Group in North China.Based on the C and Mg isotope data,we developed a numerical model to quantify the carbon source of calcite veins.The modeling results indicate that4–37 wt%of carbon in these calcite veins was derived from atmospheric CO2.The low contribution from atmospheric CO2might be attributed to the host limestone that might have diluted the atmospheric CO2sink.Nevertheless,taking this value into consideration,it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2within 2000 years,i.e.,soil carbonate alone would sequester all atmospheric CO2within 1 million years.Finally,our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate.展开更多
Nearly 18 years after the proposal of the weathering-related carbon sink concept(Berner R A.Weathering,plants and the long-term carbon cycle.Geochim Cosmochim Acta,1992,56:3225-3231),it is an appropriate timing to re-...Nearly 18 years after the proposal of the weathering-related carbon sink concept(Berner R A.Weathering,plants and the long-term carbon cycle.Geochim Cosmochim Acta,1992,56:3225-3231),it is an appropriate timing to re-evaluate its geological context with the updated dataset.Ryskov et al.(Ryskov Ya G,Demkin V A,Oleynik S A,et al.Dynamics of pedogenic carbonate for the last 5000 years and its role as a buffer reservoir for atmospheric carbon dioxide in soils of Russia.Glob Planet Change,2008,61:63-69) lately claimed that in the course of soil formation for the last 5000 years the soils of Russia fixed atmospheric carbon dioxide as pedogenic carbonate during the arid periods at a rate of 2.2 kg C/(m2 a) in chernozem,1.13 kg C/(m2 a) in dark-chestnut soil,0.86 kg C/(m2 a) in light-chestnut soil,on the basis of carbon isotopic data;however,their interpretations of the data do not appear straightforward nor persuading,and thus their claim is likely misleading.Their interpretations are also contrary to the conclusions drawn by Dart et al.(Dart R C,Barovich K M,Chittleborough D J,et al.Calcium in regolith carbonates of central and southern Australia:Its source and implications for the global carbon cycle.Palaeogeogr Palaeoclimatol Palaeoecol,2007,249:322-334) who found that Australian regolith carbonates did not capture any additional CO2;instead the carbonate was simply being remobilized from one pool to another.Here we raise comments to these explanations on the following two issues:(1) origin of pedogenic carbonate:silicate weathering vs.carbonate weathering,and(2) problems in using carbon isotopic technique to distinguish carbonates formed by silicate weathering and carbonate weathering.It is concluded that pedogenic carbonate may not be an important atmospheric CO2 sink at all,i.e.carbonate weathering-related pedogenic carbonate does not capture any additional CO2,while the CO2 capture in silicate weathering-related pedogenic carbonate is small in short-term time scales due to the slow kinetics of silicate weathering展开更多
土壤无机碳在固碳、维持土壤质量、促进有机碳稳定性与肥力和生态系统服务功能等方面有重要作用。以Web of Science核心合集数据库和CNKI数据库中472篇土壤无机碳研究的文献为数据源,通过VOSviewer、CiteSpace和HistCite分别从发文量、...土壤无机碳在固碳、维持土壤质量、促进有机碳稳定性与肥力和生态系统服务功能等方面有重要作用。以Web of Science核心合集数据库和CNKI数据库中472篇土壤无机碳研究的文献为数据源,通过VOSviewer、CiteSpace和HistCite分别从发文量、被引频次、合作强度及关键词等角度对发文国家、机构、作者、研究热点及其变化趋势进行计量分析与可视化展示。结果表明:2003~2023 a期间土壤无机碳研究的发文数量不断增长,主要从土壤学与环境学向其他学科延伸;科研机构以中国科学院为首,而发文作者形成了以Kuzyakov Y为核心的作者群,总体而言我国的发文量和国际影响力最大。当前的研究热点集中在土壤无机碳储量及其影响因素,土壤无机碳在碳循环中的作用及其固碳潜力,土壤无机碳的生态系统服务功能等方面。然而,当前对碳酸盐再沉淀过程中有机碳向无机碳的转移及固碳作用研究不足,尤其是植物光合同化碳向土壤次生碳酸盐累积转化及对氮肥的响应机制尚不清楚。今后应通过实地研究收集无机碳数据并结合机器学习建模等方法,提高估算全球碳库及碳周转速率的准确性;深化土壤有机碳-二氧化碳-土壤无机碳的转化机理,进一步明晰无机碳对稳定土壤碳库和维持土壤健康等生态服务方面的作用。展开更多
文摘lsotopic analyses for paleovegetational evolution have been carried out on samples of the pedogenic carbonate nodules in the Red Clay-Loess sequence at Lingtai （35°N）, the Loess Plateau. Stable carbon isotopic composition indicates that （ ⅰ ） C<sub>4</sub> plants might be present at least by7.0 Ma; （ ⅱ ） C<sub>4</sub> plants expanded gradually between ～4.0 and ～3.2 Ma, and their biomass fraction was up to 50%; and （ ⅲ ） the biomass of C<sub>4</sub> vegetation since ～2.0 Ma seems to have been decreased to the level （about 20%） before 4.0 Ma. C<sub>4</sub> plant expansion at Lingtai cannot be fully understood with the 'global C<sub>4</sub> expansion' model because it occurred much later up to 3.0 Ma than in Pakistan, which indicates that some changes in the regional climatic system may also contribute to C<sub>3</sub>/C<sub>4</sub> shift except changes in atmospheric CO<sub>2</sub> concentrations and temperature. The latitudinal zone for C<sub>3</sub>/C<sub>4</sub> transition seems to move southwards slightly in East Asia, compared with the case in North America where 37°N is the ideal
基金supported by the National Basic Research Program of China (2010CB950200)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-117)the National Natural Science Foundation of China (40730104)
文摘Carbon isotopes of pedogenic carbonate are often used to study paleoenvironments, but the existence of detrital carbonate changes the carbon isotopic composition. To develop an experimental method to determine existence of detrital carbonate in carbonate nodules, and to avoid it during isotope analysis, 23 pedogenic carbonate nodules in Miocene loess from the Loess Plateau of China were studied through micromorphology and carbon isotope analysis. The difference in carbon isotopic composition between matrix carbonate (B) and pore carbonate (A) (δ 13C(B-A)) ranges from 0.27‰ to 0.44‰ in nodules containing detrital carbonate and -0.16‰ to 0.13‰ in nodules where detrital carbonate is absent. The latter is within measurement error, but the former is beyond it. Here we propose an isotopic approach to determine if nodules contain detrital carbonate: if δ 13C(B-A) is within the measurement error, the nodules do not contain detrital carbonate, and vice versa. We suggest that it is better to analyze pore carbonate instead of matrix carbonate when using carbon isotope of carbonate nodules to reconstruct paleoenvironments.
基金supported by the National Natural Science Foundation of China(91325301,41130530,41371224,41601221)
文摘Knowledge of soil carbon（C） distribution and its relationship with the environment can improve our understanding of its biogeochemical cycling and help to establish sound regional models of C cycling. However, such knowledge is limited in environments with complex landscape configurations. In this study, we investigated the vertical distribution and storage of soil organic carbon（SOC） and soil inorganic carbon（SIC） in the 10 representative landscapes（alpine meadow, subalpine shrub and meadow, mountain grassland, mountain forest, typical steppe, desert steppe, Hexi Corridor oases cropland, Ruoshui River delta desert, Alxa Gobi desert, and sandy desert） with contrasting bioclimatic regimes in the Heihe River Basin, Northwest China. We also measured the 87 Sr/86 Sr ratio in soil carbonate to understand the sources of SIC because the ratio can be used as a proxy in calculating the contribution of pedogenic inorganic carbon（PIC） to total SIC. Our results showed that SOC contents generally decreased with increasing soil depth in all landscapes, while SIC contents exhibited more complicated variations along soil profiles in relation to pedogenic processes and parent materials at the various landscapes. There were significant differences of C stocks in the top meter among different landscapes, with SOC storage ranging from 0.82 kg C/m^2 in sandy desert to 50.48 kg C/m^2 in mountain forest and SIC storage ranging from 0.19 kg C/m^2 in alpine meadow to 21.91 kg C/m^2 in desert steppe. SIC contributed more than 75% of total C pool when SOC storage was lower than 10 kg C/m^2, and the proportion of PIC to SIC was greater than 70% as calculated from Sr isotopic ratio, suggesting the critical role of PIC in the C budget of this region. The considerable variations of SOC and SIC in different landscapes were attributed to different pedogenic environments resulted from contrasting climatic regimes, parent materials and vegetation types. This study provides an evidence for a general trade-off pattern between SOC
基金funded by the National Key Technology Program during the 13th Five-Year Plan Period (Grant No. 2016ZX05034001-007)National Natural Science Foundation of China (Grant No. 41772359)
文摘The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,while the development of soil profiles would account for both organic and inorganic carbon burial.As compared with soil organic carbon,inorganic carbon burial,collectively known as the soil carbonate,would have a greater impact on the long-term carbon cycle.Soil carbonate would have multiple carbon sources,including dissolution of host calcareous rocks,dissolved inorganic carbon from freshwater,and oxidation of organic matter,but the host calcareous rock dissolution would not cause atmospheric CO2drawdown.Thus,to evaluate the potential effect of soil carbonate formation on the atmospheric p CO2level,different carbon sources of soil carbonate should be quantitatively differentiated.In this study,we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop,consisting of limestone of the early Paleogene Guanzhuang Group in North China.Based on the C and Mg isotope data,we developed a numerical model to quantify the carbon source of calcite veins.The modeling results indicate that4–37 wt%of carbon in these calcite veins was derived from atmospheric CO2.The low contribution from atmospheric CO2might be attributed to the host limestone that might have diluted the atmospheric CO2sink.Nevertheless,taking this value into consideration,it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2within 2000 years,i.e.,soil carbonate alone would sequester all atmospheric CO2within 1 million years.Finally,our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate.
基金supported by the Hundred Talents Program of the Chinese Academy of Sciencesthe National Natural Science Foundation of China (40872168)
文摘Nearly 18 years after the proposal of the weathering-related carbon sink concept(Berner R A.Weathering,plants and the long-term carbon cycle.Geochim Cosmochim Acta,1992,56:3225-3231),it is an appropriate timing to re-evaluate its geological context with the updated dataset.Ryskov et al.(Ryskov Ya G,Demkin V A,Oleynik S A,et al.Dynamics of pedogenic carbonate for the last 5000 years and its role as a buffer reservoir for atmospheric carbon dioxide in soils of Russia.Glob Planet Change,2008,61:63-69) lately claimed that in the course of soil formation for the last 5000 years the soils of Russia fixed atmospheric carbon dioxide as pedogenic carbonate during the arid periods at a rate of 2.2 kg C/(m2 a) in chernozem,1.13 kg C/(m2 a) in dark-chestnut soil,0.86 kg C/(m2 a) in light-chestnut soil,on the basis of carbon isotopic data;however,their interpretations of the data do not appear straightforward nor persuading,and thus their claim is likely misleading.Their interpretations are also contrary to the conclusions drawn by Dart et al.(Dart R C,Barovich K M,Chittleborough D J,et al.Calcium in regolith carbonates of central and southern Australia:Its source and implications for the global carbon cycle.Palaeogeogr Palaeoclimatol Palaeoecol,2007,249:322-334) who found that Australian regolith carbonates did not capture any additional CO2;instead the carbonate was simply being remobilized from one pool to another.Here we raise comments to these explanations on the following two issues:(1) origin of pedogenic carbonate:silicate weathering vs.carbonate weathering,and(2) problems in using carbon isotopic technique to distinguish carbonates formed by silicate weathering and carbonate weathering.It is concluded that pedogenic carbonate may not be an important atmospheric CO2 sink at all,i.e.carbonate weathering-related pedogenic carbonate does not capture any additional CO2,while the CO2 capture in silicate weathering-related pedogenic carbonate is small in short-term time scales due to the slow kinetics of silicate weathering
文摘土壤无机碳在固碳、维持土壤质量、促进有机碳稳定性与肥力和生态系统服务功能等方面有重要作用。以Web of Science核心合集数据库和CNKI数据库中472篇土壤无机碳研究的文献为数据源,通过VOSviewer、CiteSpace和HistCite分别从发文量、被引频次、合作强度及关键词等角度对发文国家、机构、作者、研究热点及其变化趋势进行计量分析与可视化展示。结果表明:2003~2023 a期间土壤无机碳研究的发文数量不断增长,主要从土壤学与环境学向其他学科延伸;科研机构以中国科学院为首,而发文作者形成了以Kuzyakov Y为核心的作者群,总体而言我国的发文量和国际影响力最大。当前的研究热点集中在土壤无机碳储量及其影响因素,土壤无机碳在碳循环中的作用及其固碳潜力,土壤无机碳的生态系统服务功能等方面。然而,当前对碳酸盐再沉淀过程中有机碳向无机碳的转移及固碳作用研究不足,尤其是植物光合同化碳向土壤次生碳酸盐累积转化及对氮肥的响应机制尚不清楚。今后应通过实地研究收集无机碳数据并结合机器学习建模等方法,提高估算全球碳库及碳周转速率的准确性;深化土壤有机碳-二氧化碳-土壤无机碳的转化机理,进一步明晰无机碳对稳定土壤碳库和维持土壤健康等生态服务方面的作用。
