陆地生态系统臭氧通量观测和气孔吸收估算研究进展

近地面大气中臭氧(O3)对植物生长发育和产量会产生不良影响。工业和交通排放的增加使得全球地面O3浓度逐年增加,不断升高的O3浓度已开始影响到我国的粮食产量。O3对植物的影响是由于其进入植物体内发生生化反应所引起的,所以需要建立一种考虑到植物生理生态状况的评估指标来评估O3对植物的影响。其中基于O3通量(特别是植物气孔吸收)的评价指标和方法,被认为比传统的基于O3浓度的评价指标和方法更符合O3对植物的影响机理。介绍了O3对生态系统影响评估方法和评价指标,重点评述了生态系统尺度O3通量观测和气孔吸收估算的主要方法以及在不同生态系统上的研究进展分析了我国关于O3对植物和生态系统影响的研究现状,并对未来的研究工作进行了展望。

A review of research on ozone flux observation and stomatal uptake estimation over terrestrial ecosystems

Ground-level ozone (O₃) is a major pollutant with adverse effects on plant growth and yield. The impact on plants is generally studied by controlling the O₃ concentration using the open top chamber (OTC) method. The effects of O₃ on ecosystems are studied by combining assessment models and indices, calculated using O₃ concentration or flux measurements over the vegetation. As these effects are related to the level of O₃ entering into the plant''s gas exchange, compared with concentration-based indices,the O₃ stomatal flux-based indices are considered the better standards for evaluating the influence of O₃ on ecosystems. In China, the rapid industrialization and urbanization has resulted in elevated O₃ concentration which is threatening crop production and yields. Studies are required to elucidate the O₃ risk-assessment indices, including consideration for the status of the plant. In this paper, we analyze the advantages and disadvantages of two kinds of assessment indices. We then introduce several O₃ flux observation and stomatal uptake estimation methods at ecosystem scale. We also review the progress in O₃ flux observations, stomatal uptake estimations and risk assessment across different ecosystems. Additionally, we present case studies and the future prospects of O₃ research in China. Concentration-based indices are easily observed and calculated, but these types of indices are often lacking sufficient, robust experimental design and data. In contrast, O₃ flux-based indices are difficult to obtain, although they incorporate the status of the ecosystem. The method used for measuring O₃ flux is mainly the eddy covariance technique, generally seen as the best modern technique. However, this method is inferior compared with CO₂/H₂O flux measurements. The lack of a fast-response O₃ analyzer is the main limiting factor. To estimate O₃ stomatal uptake, one of the well-established methods uses a resistance model for partitioning the total O₃ flux. Stomatal and non-stomatal resistance can be estimated by parameterizing or converting CO₂/H₂O resistance, which can be estimated using the empirical methods or the Penman-Monteith equation. O₃ deposition velocity (V_d) is a better variable to compare O₃ deposition characteristics across different ecosystems and the V_d value may be affected by the underlying surface status and atmospheric conditions. The V_d on abiological surfaces (0.1 cm/s or less) is much lower than on the surface of the vegetation. Generally, V_d over forest ecosystems (1 cm/s) is larger compared with that over grassland and cropland ecosystems (0.5 cm/s). Radiation and atmospheric humidity are the main factors controlling O₃ deposition. Fractions of stomatal uptake over different locations and ecosystems vary considerably with leaf size, stomatal aperture, canopy structure and the physiology of plants. For ecosystem risk assessment, the performance of flux-based indices was better compared with concentration-based indices over various ecosystems. In China, most research focuses on the effects of different O₃ concentrations on crop growth and yield using the OTC method, obtaining some significant results. There are relatively few studies that have investigated the effects of O₃ concentration and flux at the ecosystem level. Therefore, relevant research on ecosystem O₃ risk assessment is urgently required in future.