土壤干旱对真桦和白桦叶片光化学效率的影响

应用叶绿素荧光技术,研究了土壤水分受限对真桦和白桦叶片光反应系统II的光化学效率影响。结果表明:土壤水分受限条件下,桦树叶片光化学效率存在域值反应,重度土壤干旱(土壤含水量13.1%～15.0%)时,两种桦树叶片实际光化学效率(ΦPSII)和表观电子传递速率(ETR)均显著降低,而轻度和中度土壤干旱时,ΦPSII和ETR与对照值差异不显著;重度土壤干旱条件下,两种桦树叶片最大光化学效率(Fv/Fm)和初始荧光(Fo)较对照没有显著差异,说明3周的土壤水分胁迫未对叶片光合机构造成实质性的损伤。土壤干旱影响叶片光化学诱导过程,且两树种间差异显著:重度干旱第3周时,真桦ΦPSII快相诱导速率由0.118 0降低到0.071 5,诱导平衡值(0.46)较对照(0.60)低;而白桦叶片ΦPSII快相诱导速率则由0.093升高到0.117,胁迫叶片和对照叶片光诱导稳定值也较接近。两种桦树叶片ΦPSII光诱导差异主要与非光化学淬灭(qN)诱导过程密切相关。

Effects of Soil Drought on Photochemical Efficiency of Betula maximowicziana and Betula platyphylla Leaves

A study was conducted to investigate the effects of soil water limitation on photochemical efficiency of Betula maximowicziana and Betula platyphylla leaves by using chlorophyll fluorescence technique.Results showed that under the limitation of soil water supply,leaf photochemical efficiency(ΦPSII) presented a significant threshold reaction.Heavy soil drought(soil water content of 13.1%-15.0%) led to significant decreases in ΦPSII and apparent electron transport rates(ETR) of the leaves,whereas light and moderate soil drought had no significant influence on ΦPSII and ETR of the leaves.At heavy soil drought,the maximum photochemical efficiency(Fv/Fm) and the initial fluorescence(Fo) of the treated leaves did not change significantly as compared with the control,which implies that soil drought for three weeks did not damage the photosynthetic apparatus substantially.Moreover,soil drought changed leaf photochemical induction process: for B.maximowicziana leaves after being treated for three weeks,the inducible rate of ΦPSII at the fast phase took on a decreasing tendency(a decrease from 0.118 to 0.0715 for the third week),and the steady induction value(0.46) of the treated leaves was lower than that of the control(0.60).In contrast,the inducible rate of ΦPSII of B.platyphylla showed an increasing trend(from 0.093 to 0.117),and the steady value of the treated leaves was close to that of the control.The difference in the photochemical induction for the two treated species had a close relation with the significant difference in the induction of non-photochemical quenching.