稳定氢氧同位素在定量区分植物水分利用来源中的应用

全球气候变化下陆地生态系统的适应性是当前科学研究关注的主题之一,了解生态系统如何响应及影响全球气候变化有利于人类对未来生存环境的预测和适应。生态系统中不同来源水分对植物生长相对贡献决的大小一定程度上决定了生态系统对气候变化的响应方式、程度和响应结果,因此跟踪和分析植物利用水分的来源是制定全球气候变化对策的一个重要研究内容。本文介绍了稳定氢氧同位素技术研究历史及其在定量区分植物利用水分的来源研究中的应用原理与具体方法。由于土壤水分在被植物根系吸收及随后沿导管向上传输的过程中,与外界环境不发生水分交换,因此不存在同位素的分馏过程,所以植物茎木质部水分同位素组成能反映出植物利用的来源水分同位素信息。通过比较植物茎木质部水分与植物利用的不同来源水分同位素值,利用二项或三项分隔线性混合模型(two-orthree-compartment linear mixing model),可以估算出植物对不同来源水分的相对使用量。而由于植物叶片水分同位素组成受到周围环境的温度、湿度、降雨和土壤水分的异质性等许多因素的影响,通过比较分析植物茎木质部水分和叶片水分同位素组成的差异可以得到植物周围环境的气候信息。植物利用水分的来源存在显著的季节性差异,并且,不同生活型植物在利用水分来源上存在明显不同。植物根系的分布及根深是决定植物利用水分来源的一个重要的因素,表层和深层根系的相对分布及其活性影响着植物吸收水分的范围。当然,利用线型分隔混合模型定量区分植物利用水分的不同来源,还有许多值得改进的地方,而且,尽管稳定同位素技术在植物科学中的应用正迅速发展起来,但利用稳定氢氧同位素来分析环境因素对植物影响的研究还只是刚刚展开,还有许多方面值得去进一步探索。

Application of stable hydrogen and oxygen isotope in analyzing plant water use sources

Adaptation of terrestrial ecosystem to global climate change, which has strong influence on human existence and development, is being paid more and more attentions. The research of terrestrial ecosystem response to climate change is crucial for human's understanding and forecasting future environmental changes. The relative contributions of different water use sources to plants will determine the fate of the response of ecosystem to global climate changes. Tracing water use sources by plants is helpful for human to determine the strategy to adapt to future environmental conditions. This paper described the principle and methods of applying hydrogen and oxygen isotope in tracing plant water use sources. Mechanisms of water uptake by plant roots and water transportation in plant xylem are non-fractionating because evaporation doesn't happen, hence plant xylem water has the same stable hydrogen and oxygen isotope composition with soil water used by plants. By analyzing hydrogen and oxygen isotope composition of plant xylem water and potential plant water sources, we can determine quantitatively the contributions of the sources to plants using two-or three-compartment linear mixing model. In contrast to plant xylem water, stable isotope composition of leave water is influenced by temperature, humidity, precipitation and many other environmental variables. Much environmental and climatic informa-tion could be understood by analyzing the difference of stable isotope composition between plant xylem water and leave water. For many species, the water sources vary with seasons, and plants with different lifestyle has different water use sources. Diversity of plant root system distribution has important influence on plant water use sources. Surface roots could absorb the water in upper soil while deeper roots often absorb groundwater or the water in deeper soil. Nowadays, stable isotopic technology has been applied in more and more ecological fields, however, further test and improvement are still needed in applying the linear mixing model to determine plant water use sources.