长白山森林优势树种对O3浓度升高的水分生理响应及机理研究

The increasing ground-level ozone concentration has caused adverse effects on the productivity and water use efficiency of temperate forest. However, the effect and mechanisms of ozone effect on whole-tree transpiration water use process and water balance are poorly understood. In Northeast China, the rapidly increasing ozone concentration has caused significant impacts on forest tree species. Because water in the xylem is transported through a complex net-work of vessels in plants, this study will explore possible underlying eco-physiological mechanisms of whole-tree level water balance to elevated ozone, and assess the influence of elevated ozone pollution on long- distance water transport in temperate forest tree species. Based on the ozone sensitivity analysis, the seedlings of dominant tree species in broad-leaved Korean pine forests of Changbai Mountain will be exposed to different ozone concentrations in open-top chambers based on the ozone sensitivity analysis. This study focuses on (1) Contrasting and analyzing the dynamic responses of transpiring water consumption and xylem water transport at whole-tree level among four tree species with differing ozone sensitivity. (2) According to the co-ordination between gaseous water transpiration and liquid hydraulic conductance, the relationships between photosynthetic characteristics and hydraulic architecture are investigated. (3) Clarifying the extent and underlying mechanisms of the effect of elevated ozone on hydraulic architecture at the whole-tree level in terms of leaf hydraulic characteristics, the xylem vessel structure of stem and root, hydraulic conductance and xylem anatomical feature. (4) Identifying the different responses and water physiological mechanisms of tree species growing under elevated ozone exposure to extreme drought event. The objectives of the research are to provide (1) a scientific basis for comprehensive understanding the effect of ozone on the physiological function of forest trees from the point of view of water physiology, and (2) a theoretical basis for reasonable prediction of population dynamics, community composition and species diversity of temperate forest.

近地层臭氧（O3）浓度持续升高改变了温带森林树木水分利用和蒸腾作用，但O3对树木蒸腾耗水和水分传导的影响机制仍未明晰。阐明O3浓度升高对树木整株水分平衡的影响程度和机制，对于认识与应对O3污染对森林生态系统的负作用具有重要意义。本研究以长白山森林不同敏感性树种（白桦、黄菠萝、水曲柳、蒙古栎）为对象，研究冠层蒸腾作用和气孔导度对O3浓度升高的响应动态和规律；将叶片的水力学性状与植株茎干、根部的木质部导管结构和导水能力相结合，揭示O3浓度升高对树木整体水分传导和水分平衡的影响机理，考虑到气态水蒸腾和液态水分传导之间的耦联作用，探讨不同O3浓度条件下树木水力结构特征和光合生理特征之间的关联关系，阐明长期生长在高浓度O3下的树木应对偶然极端干旱事件的响应差异及机制，从水分生理角度为理解O3浓度升高对森林树木生理学功能的影响提供参考，为合理预测未来森林群落组成和演替提供理论基础。

近地层臭氧（O3）浓度升高改变了温带森林树木水分利用和蒸腾作用，阐明O3浓度升高对树木整株水分平衡的影响程度和机制，对于认识与应对O3污染对森林生态系统的负影响具有重要的科学意义。本研究采取模拟实验与定点监测相结合的方法，研究O3浓度升高对长白山森林典型树种树木冠层蒸腾作用和气孔导度的影响规律，考虑到气态水蒸腾和液态水分传导之间的耦联作用，探讨O3浓度升高条件下树木水力结构特征和光合生理特征之间的关联关系。研究结果为：O3浓度升高对气态水分散失与液态水分传导过程、生物量分配均可造成显著影响。与环境大气相比，O3浓度升高显著降低了树木整株水平的水力导度、单位根重与单位叶面积的根系水力导度。这表明植物末端组织根系的木质部导水功能更易受到O3浓度升高的影响。并且O3浓度升高引起的气体交换参数的变化与根系水力导度的变化均呈显著正相关关系（P < 0.05），说明根系水分传输与植物光合响应之间在应对O3浓度升高时出现了强烈的协同作用。在水分传输安全方面，O3浓度升高造成不同树种在自然干燥过程中气孔导度变化模式发生改变，影响植物水分蒸腾和散失。同时，O3浓度升高显著增加了木质部气穴化栓塞程度、降低水分利用效率和叶片持水能力，这可能会造成植物无法保持足够高的水势，正如在自然干旱过程中观察到O3浓度升高处理下植物叶片更容易萎蔫和脱落。此外，研究结果证实比叶重较小的树种其气孔对臭氧的响应更为敏感，冠层中上层受到的氧化伤害较新叶和底层老叶更大，H2O2累积较多。O3浓度升高不仅会影响植物光合作用，也会造成叶片木质部水分传输功能丧失，直接和/或间接影响植物光合-水分关系，影响植物对其他环境因子的应对能力。本项目从水分生理角度为理解O3浓度升高对森林树木生理学功能的影响提供参考，为合理预测未来森林群落组成和演替提供理论基础。