ACTA ECOLOGICA SINICA Volume 26, Issue 3, March 2006 Online English edition of the Chinese language journal Cite this article as: Acta Ecologica Sinica, 2006, 26(3), 823−829. Received date: 2005-07-27; Accepted date: 2006-02-08. *Corresponding author. E-mail:wangxk@rcees.ac.cn Copyright © 2006, Ecological Society of China. Published by Elsevier BV. All rights reserved. RESEARCH PAPER Response of gas exchange of rape to ozone concentration and exposure regime Feng Zhaozhong 1 , Wang Xiaoke 1, * , Zheng Qiwei 1 , Feng Zongwei 1 , Xie Juqing 2 , Chen Zhan 1 1 State Key Lab of System Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 2 North-western Sci-Tech University of Agriculture and Forestry, Yangling 712100, China Abstract: Gas exchange characteristics, Pn-PAR and/or Pn-CO 2 response parameters of rape (Brassica napus L) were studied in the field under different O 3 concentrations (CF, 50 nl·L －1 and 100 nl·L －1 ) and fumigation regimes (constant concentration and dynamic varying concentrations) with a portable photosynthetic system (CIRAS-1). Results indicated: (1) Relatively to CF, higher ozone con- centration decreased in Tr and increased in WUE under a constant concentration fumigation regime. In addition, an increase in Tr and decreases in Pn, Gs and WUE were found in the dynamic ozone exposure regime; (2) In the constant concentration exposure re- gimes, AQY, LSP and P max were markedly reduced and Rp and Г were enhanced with an increase in ozone concentration (100 nl·L －1 ). There were significant differences in the parameters such as Rd, LCP, LSP, P max and CE between O 3 exposure regimes; (3) Regard- less of the exposure regimes which were imposed, the increase of O 3 concentration induced significant decreases in Fv/Fo and Fv/Fm of the eighth leaves from the top canopy, but it had no effect on the fifth full-spread leaves. It can be concluded that the dy- namic ozone exposure regime has greater detrimental effects on the photosynthesis of rape in spite of equal exposure dose, and thus is unfavorable for plant growth and the accumulation of dry matter. Key Words: ozone; rape; photosynthetic characters; carboxylation efficiency; apparent quantum yield; chlorophyll a fluorescence In recent decades, ambient ozone has increased at an annual rate of 0.5%–2.5% because of the overuse of fossil fuels. Ozone pollution episodes occurred frequently and their duration, intensity and detrimental effects increased continuously [1－2] . As predicted by IPCC (2002), if current levels of anthropogenic activity were maintained, ambient ozone average concentra- tion in the summer would exceed 70nl·L －1 in the Northern Hemisphere mainland at the end of the century [3] . In China, ambient ozone increased rapidly, with its average concentra- tion reaching 50–60nl·L －1 , which exceeds the national air quality criterion. The ozone level in developed eastern regions was 20nl·L －1 higher than in western regions [4] . Ozone pollu- tion has been diffused to non-urban areas due to long-distance transport [5] . It has been demonstrated that a high ozone level in the tro- posphere was the most important phytotoxic gaseous pollutant in many parts of the world, leading to a reduction in the yield of many crops along with a decline in forests [4, 6－9] . In 1956, Erickson et al. found that ozone could restrain the photosyn- thesis rate of the hydrophyte Lemna minor [10] . Subsequently, the fact that ozone significantly reduced the photosynthesis rate, was also found in many crops such as wheat, rice, beans, potatoes and spinach [4,11－13] . Moreover, the influence of ozone on the photosynthesis rate was related with stages of plant growth [14] . However, the above results were based on a con- stant concentration fumigation regime. In fact, ozone has a marked diurnal and seasonal change pattern in the atmos- phere [15] . It is obvious that a dynamic fumigation regime can really simulate the response process of plants to increasing ambient ozone (diurnal change), and more scientifically evaluate the yield loss of crops. Therefore, this experiment was carried out with rape to compare the response of gas ex- change characteristics of rape to different O 3 concentrations and fumigation regimes (constant concentration compared to dynamic varying concentration with equal ozone dose) in the field, and to clarify the possible mechanism of a reduced pho- tosynthesis rate by ozone from the response of light intensity and CO 2 concentration.