The features of changes in chlorophyll fluorescence in response to the water status of four woody species of Sophora japonica, Populus x canadensis, Gingkgo biloba and Pinus thunbergii were analysed in terms of their drought resistance. The analysis was carried out with the fast - induction kinetics associated with chlorophyll fluorescence and changes of relevant parameters in leaves of detached twigs during desiccation stress with a Handy PEA chlorophyll fluorometer. The results showed that with the progression of dehydration, the fast-induction kinetics of chlorophyll fluorescence in the four species changed significantly. The maximum primary yield of photochemistry of photosystem II (Fv/Fo) , maximum quantum yield for primary photochemistry (Fv/Fo) , performance index (PI) all declined, with S. Japonica having the fastest decrease, followed by P. X canadensis, G. Biloba and P. Thunbergii, suggesting that their toleration to dehydration was in the same order accordingly. However, the threshold of relative water content (RWC) for the fast-induction kinetics associated with chlorophyll fluorescence was 60% -70% , 40% -50% , 30% -40% and 10% -20% for P. Thunbergii, G. Biloba, P. X canadensis and S. Japonica, respectively, indicating that the resistance of photosystem to dehydration of the plants was in a reversed order. It is concluded that S. Japonica and P. X canadensis have had a higher tolerance to dehydration, but higher rate of water use, suggesting they are not 'suitable for arid environments; whereas P. Thunbergii has had a higher resistance to dehydration, but their inner tissues have had lower tolerance, suggesting it is suitable for semi-arid or dry sub-humid environment; However, G. Biloba is intermediate between the above two types of plants in terms of the adaptability to water regimes.%以自然生长的国槐、加杨、银杏和黑松的离体枝叶为材料,利用连续激发式叶绿素荧光仪测定脱水过程中叶绿素快速荧光动力学曲线及相关参数的变化,以分析4种树木叶绿素荧光特性随体内水分状况的变化规律及其耐旱特点.结果表明:随着脱水的延续,4种树木的叶绿素荧光动力学曲线发生明显的变化,主要荧光参数Fv/Fm,Fv/Fo,PI等逐渐降低,说明PSⅡ的光化学效率、潜在活性和整个光合电子传递链的效率等均随脱水而下降.以离体后脱水时间为横坐标,主要荧光参数Fv/Fm,Fv/F.,PI等的下降表现为国槐最快、杨树次之、银杏较慢、黑松最慢,即4种树木抗脱水能力依次增强;但4种植物叶绿素荧光参数快速降低的RWC阈值分别为国槐10％～20％、杨树30％ ～40％、银杏40％～50％、黑松60％ - 70％,表现为光合系统对脱水的耐力依次降低.可见,国槐和杨树对脱水有较强的耐受力,但失水快、耗水多,难以适应缺水的环境;黑松抗脱水能力强、耗水少,但对体内水分亏缺的耐受力不强,可以适应半干旱和半湿润环境;银杏的适应性介于上述2类之间.
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