典型城市绿化树种的臭氧敏感性差异及生物学机制研究

With the acceleration of urbanization, urban atmospheric pollution is becoming a worsening problem; especially, the increasing summer ozone (O3) concentrations have directly impact on the growth and development of urban greening trees and their ecological services. Therefore, scientific evaluation troposphere O3 pollution impact on ecological processes of urban greening tree species has the vital theoretical and practical significance. Using the open-top chamber system, the project studies on the sensitivity response of the native greening tree species widely planted in Beijing on the increasing atmospheric O3 concentrations by the fumigation experiments of short-term high O3 concentration and long-term low O3 concentration. The aim is quantitatively screening the O3 sensitivity of the trees by observing tree damage symptoms and their occurrence time, photosynthetic rate and the change of leaf tissue structure; and further systematically reveals the eco-physiological mechanisms of the differences O3 influence on the greening trees from the aspects of leaf stomatal characteristics, antioxidant system, leaf character attributes and 13C isotope abundance, and establish the effective evaluation index of urban tree species O3 sensitivity. Also, we develop stomatal O3 flux model, establish the response relationship of differently sensitive trees between stomatal O3 absorption flux and biomass of plant and the water use efficiency. The project could comprehensively provide theoretical reference for the selection both anti-O3 pollution and efficient utilization of water resources of urban greening tree species, and also provide quantitative scientific basis for the development of the standards of protecting air quality of urban forest in our country.

随着城市化进程的加快，大气污染日益加重，尤其是夏季臭氧浓度的不断增加直接影响到城市绿化树木的生长发育和生态服务功能。因此科学评价近地层O3污染对我国典型城市绿化树种生态过程的影响具有重要的理论和现实意义。本项目利用开顶式熏气系统，通过高O3浓度短期和低O3浓度长期熏蒸，研究北京市广为栽植的乡土绿化树种对大气O3浓度增加的敏感性响应差异及机制。通过观测叶片的伤害症状出现时间、光合速率和叶片组织结构，定量筛选出城市绿化树种的O3敏感性；从叶片气孔特征、抗氧化系统、叶片性状属性和13C同位素丰度方面系统揭示O3对绿化树种影响差异的生理生态学机制，建立城市绿化树种的O3敏感性有效评价指标。开发气孔O3通量模型，建立不同敏感性树种的气孔O3吸收通量与植物生物量及水分利用效率的响应关系，为北京筛选抗O3且高效利用水分的城市园林绿化树种提供理论参考，为制定保护我国城市森林空气质量标准提供定量的科学依据。

随着我国城市化进程的加快，城市大气O3污染日益加重。夏季O3浓度高发期（6-8月）与植物的生长季同步，严重威胁城市森林的生态系统健康。因此科学评价地表O3污染对典型城市绿化树种生态过程的影响具有重要的理论和现实意义。本项目利用野外开顶式熏气系统（OTCs），设置对照CF（过滤大气，[O3]＜20ppb）和高浓度NF80（环境大气+80ppb[O3]）2个处理，对21种落叶和常绿木本植物的一年生树木的叶片伤害症状、解剖结构、气体交换、抗氧化生理生化指标和比叶重等进行了研究。包括珍珠梅、木槿、白蜡、杨树、榉树、金银木、复叶槭、榆树、合欢、珍珠绣线菊、暴马丁香、水蜡、天目琼花、西府海棠、胶东卫矛、金叶女贞、冬青、法桐、国槐、刺槐和臭椿。通过观测叶片的伤害症状及首次症状出现时间，定量了21种木本植物的O3敏感性，发现珍珠梅、木槿和白蜡是对O3最敏感的树种，并且落叶树种的O3敏感性高于常绿树种。通过测定光合速率、气孔导度、比叶重、组织解剖结构和抗氧化物质，发现树种的O3敏感性差异是由叶片功能属性比叶重以及基于面积的抗氧化水平所决定，而非基于质量的抗氧化水平或者气体交换参数。比叶重越大（栅栏组织和海绵组织越厚）的树种其抗性越强。因此，木本植物对O3浓度升高的敏感性响应差异是由比叶重和基于面积的抗氧化水平决定。作为简便易测的指标比叶重，可用来作为筛选城市抗O3污染绿化树种的有效评价指标。