中文摘要：

在新疆气候生态条件下，采用膜下滴灌植棉技术，设置不同滴灌水分处理，研究了不同滴灌量条件下棉花（Gossypiumhirsutum）苞叶和叶片碳同化、光呼吸作用、光系统II（PSII）热耗散作用及其光破坏防御机制的差异，以揭示滴灌节水条件下棉花苞叶缓解光抑制的机理及与棉花抗旱特性的关系。结果表明：棉花开花后苞叶及叶片在高温强光下实际光化学效率（ФPSII）显著降低，发生明显的光抑制现象，但苞叶的光抑制程度较叶片轻；与正常滴灌量处理相比，节水滴灌条件下棉花水分亏缺，叶片净光合速率（Pn）、ФPSII、光呼吸（Pr）、光化学猝灭系数（qp）降低，非光化学猝灭系数（NPQ）升高，叶片光抑制程度加重，而苞叶Pn、ФPsII、pr、Pr、NPQ变化不大，与正常滴灌量处理相比，光抑制程度无显著差异。苞叶光呼吸速率与光合速率的比值（Pr／Pn）显著高于叶片；滴灌节水条件下棉花适度水分亏缺对苞叶光呼吸及Pr/Pn无显著影响。高温强光下，棉花节水滴灌对叶片PSII量子产量的转化与分配影响显著，但对苞叶的影响不显著；苞叶非调节性能量耗散的量子产量（Y（NPQ））高于叶片，因此能有效地将PSII的过剩光能以热的形式耗散。综上所述，与叶片相比，苞叶对轻度水分亏缺不敏感，是棉花适应干旱逆境较强的器官，苞叶光呼吸和热耗散作用对光破坏防御具有重要意义。

英文摘要：

Aims Photorespiration and non-photochemical quenching of chlorophyll fluorescence in photosystem II （PSII） were studied in bracts and leaves of cotton （Gossypium hirsutum） plants, in order to investigate the photoprotec- tive mechanisms and drought tolerance in cotton bracts under field conditions of water-saving drip irrigations. Methods Gas exchange and chlorophyll fluorescence parameters of PSII were analyzed in bracts and leaves of cotton plants after anthesis. The study was conducted with two treatments comprising normal drip irrigation （5 228.5 m3.hm-2） and water-saving drip irrigation （3 874.1 m3.hm-2） under field conditions. Important findings The actual photochemical efficiency of PSII （ФPSII） decreased in both bracts and leaves of cotton plants after anthesis under water-saving drip irrigation, but the magnitude of decrease was less in bracts than in leaves. Results showed the bracts experienced less severe photoinhibition than leaves. The rate of net photosynthesis （Pn）, ~sn, net photorespiration （Pr）, photochemical quenching （qp）, and non-photochemical quench- ing （NPQ） decreased in the leaves of cotton plants under water-saving drip irrigation, but no significant difference was observed in the bracts. With decreasing water supply, the Pr/Pn in bracts was much higher than that in leaves and water deficit had no significant effect on the Pr/Pn in bracts. The results of chlorophyll fluorescence parame- ters showed that the quantum yield of regulated energy dissipation （Y（NPQ）） was higher in bracts than in leaves under high irradiance and temperature conditions, and that the thermal dissipation in bracts was not susceptible to water deficit, thus protecting the photosynthetic apparatus against photodamage. Overall, both photorespiration and energy dissipation in bracts were found to alleviate photoinhibition and played important roles in protecting PSII in cotton plants.