中文摘要：

在盆栽条件下,以杂交棉泗杂3号为材料,以花铃期正常灌水[土壤相对含水量（SRWC）（75±5）%]为对照,设花铃期SRWC（60±5）%和SRWC（45±5）%持续干旱50 d两个处理,研究棉铃对位叶气体交换参数和叶绿素荧光参数在持续干旱过程中的动态变化和响应机制.结果表明：SRWC（60±5）%处理0~21 d棉铃对位叶的净光合速率（Pn）、气孔导度（gs）、胞间CO2浓度（Ci）下降,气孔限制值（Ls）上升,叶绿素荧光参数无显著变化,Pn下降的主要原因是气孔限制;处理21~49 d棉铃对位叶Pn持续下降,Ci上升,Ls下降,同时最大光化学效率（Fv/Fm）、实际光化学效率（ΦPSII）和光化学猝灭系数（qP）显著降低,非光化学猝灭系数（NPQ）先升后降,Pn下降的主要原因是非气孔限制;此时叶片PSII系统受到损伤,光合机构及光合酶系统被破坏,同时成铃强度急剧下降,成铃数降低,导致产量下降.SRWC（45±5）%处理0~14 d棉铃对位叶Pn、gs、Ci显著下降,Ls急剧上升,Fv/Fm、ΦPSII、qP无显著变化,Pn下降主要由气孔限制引起;处理14~49 d,棉铃对位叶Pn缓慢下降,Ci上升,Ls下降,Fv/Fm、ΦPSII和qP不断降低,而NPQ先升后降,表明Pn下降主要由非气孔限制引起,同时成铃强度急剧下降,成铃数减少,产量降低.本试验条件下,SRWC（60±5）%和SRWC（45±5）%处理下棉花生长的临界胁迫时间分别为21和14 d.

英文摘要：

To investigate the dynamic changes and response mechanisms of gas exchange parameters and fluorescence indices of the subtending leaf to cotton boll under soil progressive drought stress, pot experiments of the hybrid cotton No. 3 were conducted with soil relative water content （SRWC） （75±5） % as control group, SRWC （60±5） % and SRWC （45±5） % as experimental groups dealt with progressive drought for 50 days. Results showed that, the net photosynthetic rate （Pn） , stomatal conductance （ gs ） and leaf intercellular CO2 concentration （ Ci ） decreased while Ls in- creased under SRWC （60±5） % for 0-21 days. Furthermore, there was no significant change in chlorophyll fluorescence indices. This indicated that stomatal limitation was the main reason for the reduction of photosynthesis of cotton. In addition, when drought for 21-49 days under SRWC （60± 5 ）%, Pnkept decreasing, while Ci began to increase and Ls began to decrease. Potential photo- chemical efficiency （Fv/Fm ）, quantum yield of photo system II （~PSII） and photochemical quenching coefficient （qp） reduced significantly, but non-photochemical quenching coefficient （NPQ） first rose then decreased. Thus, non-stomatal limitation was the main reason why the photo- synthesis of cotton reduced. Photosynthetic organization and photosynthetic enzyme system were de-stroyed, boll setting intensity reduced and the number of boll and yield reduced significantly. Drought for 0-14 days under SRWC （45±5） % treatment led to sharp decrease in Pn, gs and Ci, whereas Ls obviously increased. There was no significant change in Fv/Fm, ФPSⅡ, qP, indicating stomatal limitation was the main reason why the photosynthesis of cotton reduced. Pn decreased slowly, while Ci began to rise and Lsbegan to decline under SRWC （45±5） % treatment for 14-49 days. Fv/Fm, ±psⅡ, qp decreased while NPQ rose first then declined, which indicated that non- stomatal limitation worked to reduce the cotton photosynthetic performance. The