| 引用本文: | 张继效，徐 海.2016.植物微体遗存分析在第四纪环境研究中的应用：综述与展望[J].地球环境学报,(3):238-253 |
| ZHANG Jixiao.2016.Application of plant microfossils in Quaternary environmental research: a review and perspective[J].Journal of Earth Environment,(3):238-253 |
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| 植物微体遗存分析在第四纪环境研究中的应用：综述与展望 |
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张继效，徐 海1,2,3
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1.中国科学院地球环境研究所 黄土与第四纪地质国家重点实验室，西安710061;2. 中国科学院大学，北京100049;3.西安交通大学 人居环境与建筑工程学院 环境科学与技术系，西安710049
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| 摘要: |
| 以孢粉、植硅体等为代表的植物微体遗存由于其分布广泛，容易保存，可反映母体植物类型的优点，在第四纪环境研究中得到了广泛应用。本文介绍了植物微体遗存的概念、常见类型，以及它们的提取方法和原理，综述了利用植物微体遗存重建古环境的传统方法和近年来发展的几种古植被与古气候定量重建方法，最后简述了植物微体遗存在年代测定、稳定同位素分析研究上的应用进展与实例。文末指出了现有研究方法的问题与不足，并对今后的多代用指标的综合研究提出了展望。 |
| 关键词: 植物微体遗存 孢粉 植硅体 提取方法 定量气候重建 稳定同位素 |
| DOI：10.7515/JEE201603003 |
| CSTR：32259.14.JEE201603003 |
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| 基金项目:国家自然科学基金项目（41473120）；国家重点基础研究发展计划（973计划）（2013CB955903） |
| 英文基金项目:National Natural Science Foundation of China (41473120); National Basic Research Program of China (973Program) (2013CB955903) |
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| Application of plant microfossils in Quaternary environmental research: a review and perspective |
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ZHANG Jixiao1,2,3
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of
Sciences, Xi’an 710061, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Department of Environment Science and Technology, School of Human Settlements and
Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, China
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| Abstract: |
| Background, aim, and scope Plant microfossils, such as sporopollen, phytoliths, starch grains and charcoals, have been widely used in Quaternary environmental research due to their features of huge quantity, wide distribution and easy preservation. However, review articles on plant microfossils in China so far have not been systematic and comprehensive enough. In this paper, key types, extraction methods and application examples in Quaternary environmental research of plant microfossils are reviewed and analyzed, and the prospects on integrated multi-proxy studies are proposed. Materials and methods Ferns spores and pollen of seed plants are collectively referred to as sporopollen, and they can be identified and categorized in different parent plants by comparing their morphologies. By analyzing the types and composition ratios of sporopollen in sedimentary strata, the vegetation composition, precipitation and temperature in the historical period may become available. Some plants such as grasses can form a type of silica-plant microfossils called phytolith, which can be preserved in the soil after its death. Different plants can form distinct or similar forms of phytolith, so phytolith can also be used in Quaternary research. Similarly, starch grains of different plants have their own characteristics and are a basis for the identification of plant species. So starch grains are expected to be used in Quaternary research, especially in archaeology. In the oceans, lakes, wetlands and other sediments, a large number of micro-algaes, such as diatoms, Charophytes oogonia, dinoflagellates, Pediastrum may appear, which are complex and diverse, and they can be categorized in the plant microfossils too. Generally, during the analytic process of sporopollen, charcoals and fungal spores can be found. Charcoals are commonly used in the study on the history of fire. Fungal spores can implicate some certain environmental information. Furthermore, some plants contain calcium oxalate crystals, which are similar to phytoliths and can be referred to as “plant calcium body”, and now studies on them are relatively less, but with the deepening of the research, they could be expected to be used in Quaternary research. Plant microfossils is dispersed in sediments and mixed with organic and inorganic impurities, so they should be separated and purified for the implementation of further research. Depending on the chemical composition of plant microfossils in different types, extraction method also has a corresponding difference. To sum up, the method to extract sporopollen mainly includes hydrofluoric acid screening method, heavy liquid flotation method and screening method, and in actual extraction process, all these methods are integratedly used. Phytoliths and diatoms are mainly composed of the silicon, and they often coexist in the sediments. To extract them, oxidants are used to remove organic components, while hydrochloric acid is used to remove the soluble carbonate minerals. Besides, sedimentation method, microwave ablation method or sieving method is used to remove clay during the extraction process of phytoliths. In physics, different sizes of particles have different sedimentation velocities in a liquid, which can be calculated by Stokes sedimentation equation. Based on this principle, the author of this article uses the low-speed centrifugation method to remove those impurities which are smaller than sporopollen or phytoliths, and finds it can replace the screening method. Sometimes, in order to speed up the extraction process and reduce the dosage of samples, heavy liquid extraction methods and so on are used to obtain various plant microfossils at the same time. Results Traditionally, plant microfossils are used in reconstructing paleoenvironment and paleoclimate by identifying their species and comparing relative quantity changes among major species in sediments. For example, the pollen ratio of Artemisia and Chenopodiaceae is often applied in analyzing humidity changes. Phytoliths and diatoms, due to their relatively poor mobility, especially in situ conservation, their content changes in sediments usually reflect the original plant condition. But for pollen, yielding quantity and propagation distance in different plants are different, so relying solely on pollen content change to rebuild paleovegetation and paleoclimate has certain limitations. To explore the quantitative relationship between pollen and vegetation or climate, surface pollen and air pollen spectrum research are widely carried out, thus providing a reliable basis for modern pollen-vegetation-climate relationship model. With the gradual replenish of the global pollen, vegetation and meteorological databases, a large number of reliable quantitative paleoclimate reconstruction methods are built, and according to their different principles they generally include: indicator species method, such as the coexistence analysis and areal overlay analysis method; multivariate function method, such as converting function method; assemblage method, such as modern analogy and response surface method. Discussion In recent years, the study on plant microfossils has transcended the limitation of morphology and expanded to their chemical composition, such as carbon isotope. For example, some sediments contain a low content on other organic matters but are rich in sporopollen, so sporopollen can be extracted for dating. Some studies show that the δ13C content of sporopollen is related to its temperature and annual precipitation. Therefore, it is expected to provide useful information during the process of reconstructing paleoenvironment. Furthermore, δ18O in phytolith has been verified of its relation to soil moisture during its growth and δ13C in diatoms of marine sediments can reflect the ocean productivity. Conclusions All in all, plant microfossils have been widely used in Quaternary research, and they have unique advantages in providing useful information in rebuilding paleovegetation and paleoenvironment, and also have potential uses in dating and stable isotope analysis. Recommendations and perspectives However, some problems still remain: the morphology of modern plant microfossils (such as pollen) requires further research; the quantitative relationship between vegetation and modern pollen etc. is not comprehensive enough; some types of plant microfossils (such as fungal spores) are lack of the research on them; stable isotope study of plant microfossils is still few, and comprehensive analysis of plant microfossils and other geochemical indicators should also be strengthened. |
| Key words: plant microfossils sporopollen phytolith extraction methods quantitative climate reconstruction stable isotope |
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