苗木离体叶片水分状况的叶绿素荧光参数定量诊断

以干热河谷区10种主要植被恢复树种为材料，探讨了苗木离体叶片室内自然失水条件下叶绿素荧光参数的响应特征，得到4点主要结论：①小桐子Jatropha curcas与印楝Azadirachta indica的叶片保水力最高，大叶相思Acacia auriculiformis与3种桉树保水力其次，3种合欢的叶片保水力最差，木豆Cajanus cajan保水力居于3种桉树与3种合欢之间。②荧光参数F_o随失水率的变化规律大致可分为主动防御型和被动抵抗型等2种类型，主动防御型树种的叶片保水力较被动抵抗型大，说明保水力越强的树种，其启动热耗散机制保护光合机构免受干旱胁迫伤害的能力越强，且水分胁迫条件下发生可逆性失活的时刻越晚。③荧光参数F_m和F_v随失水率的增大总体上呈显著下降趋势，F_v /F_m和F_mv /F_ms随失水率的增大总体上呈逐渐下降的趋势，下降轨迹近似于一条水平抛物线，在F_v /F_m和F_mv /F_ms下降的过程中，各树种均存在1个突降点，该点为PSⅡ反应中心失活过程中的关键点。④荧光参数F_mv /F_ms比F_v /F_m能更灵敏地指示叶片光合机构遭受水分胁迫的重大伤害状况，荧光参数F_v /F_m和F_mv /F_ms与叶片失水率呈现很强的数量相关关系，具有作为植物叶片水分状况诊断指标的广阔前景。图4表2参17

Fluorescence parameters for drought stress diagnosis in detached leaves of ten tree species

The response to drought stress for fluorescence parameters from detached leaves of 10 tree species used for vegetative restoration in hot, dry valleys was undertaken. Results showed that： 1） Jatropha curcas and Azadirachta indica leaves had the highest water holding capacity followed by Acacia auriculiformis and three Eucalyptus species （E. camaldolensia, E. citriodora and E. globulue）, then followed by Cajanus cajan, Albizia kalkor and Leucaena glauca with Acacia glauca having the lowest. 2） Differences in water-loss rate （WLR） for the fluorescence parameter Fo were divided into two types： initiative and passive resistance types. The initiative resistance type had a higher leaf water holding capacity than the other type, meaning the tree species with high leaf water holding capacity had a greater capacity to avoid harm from drought-stress by starting a heat dissipation mechanism to protect photosynthetic organs and by delaying the reversible vitality loss which occurred with water stress. 3） Fluorescence parameters Fm and Fv either decreased as WLR increased; Fv /Fm and Fmv /Fms had a predominantly linear decrease. For each species the decrease in Fv /Fm and Fmv /Fms had a sharp downward dip, which could be the key point where the PSⅡ reaction centre lost its vitality. 4） Fmv /Fms could be more sensitive to damage of the PSⅡ reactioncentre than Fv /Fm; however, both parameters showed a significantly quantitative relationship to the leaf WLR. Thus, Fv /Fm and Fmv /Fms offered a possible diagnostic index for a plant’s leaf water status.