苔藓硼同位素分馏机理及其对大气硼沉降的指示

Boron is an essential trace nutrient element for plants growth. The uptake of boron by plants is an important part for the surface boron biogeochemical cycle. Because of the distinct physiological characteristics and structural feature, moss has unique advantages in the ecological monitoring for atmospheric deposition. The accumulating ability of moss for boron is relatively strong. So far, the sources of boron and mechanisms of isotopic fractionation in moss are still uncertain, which hinder the recognition of physiology, cyclic process and implications significance of boron in moss. Combined theories of geochemistry and bryology, this proposal aimed at exploring the mechanisms of moss boron utilization and their isotopic effects. Through laboratory culture experiments, the boron isotopic compositions and utilization of boron in moss and their controlling factors will be revealed. After continuously sampling and analysis of dry and wet deposition and moss in the Loess Plateau, the accumulation mechanisms and time model of boron in moss will be discussed. Combined with culture experiments, the feasibility of using boron isotopic compositions in moss for atmospheric deposition will be evaluated. By comparison boron isotopic compositions in moss in different environments and species, the moss specie can be used for environmental tracing and its growing environment will be revealed. Based on the boron isotopic compositions of the same moss in different places, the response of isotopic compositions in moss to environmental parameters, such as temperature, humidity, and rainfall will be clarified, and the influence of boron utilization by moss to boron cycle and its application prospect will be verified. This proposal will replenish the fractionation mechanisms of boron isotope, provide theoretical basis for the researches of boron geochemical cycles, and expand the application area of boron isotope.

硼是植物生长必需的微量营养元素，植物硼利用是硼生物地球化学循环的重要环节。特殊的生理和结构特征使苔藓在大气沉降的生态监测方面具有独特优势。苔藓硼富集能力较强，但其来源和同位素分馏机理并不清楚，阻碍了对苔藓硼生理、循环过程及指示意义的深入认识。本项目地球化学和植物学结合，系统研究苔藓硼利用机理及同位素效应。通过培养实验，揭示苔藓生长时的硼同位素组成变化特征、利用原理及控制因素。通过黄土高原地区干湿沉降和苔藓的连续采集与分析，探讨苔藓硼累积机制和时间模式。结合培养实验，验证苔藓硼浓度及同位素组成指示大气硼沉降的可行性。根据不同生境和属种苔藓硼同位素组成差异，明确适合环境示踪的苔藓种类和生境。根据同种苔藓硼同位素组成的空间变化特征，阐明其对温度、湿度、降雨量等参数的响应，评价苔藓硼利用对硼循环的影响及应用前景。本项目将完善硼同位素分馏机理，为硼生物地球化学研究提供理论依据，拓展硼同位素应用领域。

苔藓在大气沉降的生态监测方面具有独特优势。苔藓硼富集能力较强，但其来源和同位素分馏机理并不清楚。本项目系统研究苔藓硼利用机理及同位素效应。通过培养实验，揭示苔藓生长时的硼同位素组成变化特征、利用原理及控制因素。通过黄土高原地区苔藓的采集与分析，结合培养实验，验证苔藓硼浓度及同位素组成指示大气硼沉降的可行性。根据同种苔藓硼同位素组成的空间变化特征，阐明其对温度、湿度、降雨量等参数的响应，评价苔藓硼利用对硼循环的影响及应用前景。.项目开展以来取得了以下主要研究成果：（1）建立了适合高有机质样品MC-ICP-MS测试的前处理和分析方法。通过干灰化、阳离子树脂与微升华相结合，建立了植物硼同位素分析的前处理方法。该方法具有操作简单、硼污染空白低的优点，并获批实用新型专利一项。（2）阐明不同植物硼同位素组成特征。对所采集的苔藓样品进行了相应的前处理工作，并对空间采集的苔藓、地软、地衣样品进行了常量、微量和硼同位素测试工作。结果显示，不同地区地软、地衣和苔藓的硼含量与同位素呈现出负相关性。苔藓、地衣、地软等无根植物的硼同位素组成可能反应了当地降水的硼同位素组成信息。（3）探索性进行了不同植物硼同位素分馏机理研究。发现从根到茎到叶，油菜和灰菜的硼同位素组成逐渐升高，叶与根之间的分馏达42‰；而从花到果壳到种子，硼同位素组成逐渐下降，这主要与硼在这些器官内的运输方式和运输载体不同有关。不同地区植物的硼同位素与生长地温度和降水相关性不明显，而主要受土壤有效硼的硼同位素组成控制。（4）通过多次尝试，在室内控制条件下，成功培养出羽枝青藓，并进行了硼同位素测定。发现苔藓的硼同位素组成与培养母液接近，表明苔藓的硼同位素组成可以用来进行大气降雨硼同位素组成的反演。研究成果在Talanta、Science of the Total Environment和Environmental Pollution上发表。本项目完善了植物硼同位素分馏机理，为硼生物地球化学研究提供理了论依据，拓展了硼同位素应用领域。