花铃期土壤持续干旱对棉铃对位叶气体交换参数和叶绿素荧光特性的影响

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(P_n)、气孔导度(g_s)、胞间CO₂浓度(C_i)下降,气孔限制值(L_s)上升,叶绿素荧光参数无显著变化,P_n下降的主要原因是气孔限制;处理21～49 d棉铃对位叶P_n持续下降,C_i上升,L_s下降,同时最大光化学效率(F_v/F_m)、实际光化学效率(Φ_PSII)和光化学猝灭系数(q_P)显著降低,非光化学猝灭系数(NPQ)先升后降,P_n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P_n、g_s、C_i显著下降,L_s急剧上升,F_v/F_m、Φ_PSII、q_P无显著变化,P_n下降主要由气孔限制引起;处理14～49 d,棉铃对位叶P_n缓慢下降,C_i上升,L_s下降,F_v/F_m、Φ_PSII和q_P不断降低,而NPQ先升后降,表明P_n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.

Effects of soil progressive drought during the flowering and boll-forming stage on gas exchange parameters and chlorophyll fluorescence characteristics of the subtending leaf to cotton boll.

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 (P_n), stomatal conductance (g_s) and leaf intercellular CO₂ concentration (C_i) decreased while L_s increased 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)%, P_n kept decreasing, while C_i began to increase and L_s began to decrease. Potential photochemical efficiency (F_v/F_m), quantum yield of photo system II (Φ_PSII) and photochemical quenching coefficient (q_P) reduced significantly, but non photochemical quenching coefficient (NPQ) first rose then decreased. Thus, non stomatal limitation was the main reason why the photosynthesis of cotton reduced. Photosynthetic organization and photosynthetic enzyme system were destroyed, 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 P_n, g_s and C_i, whereas L_s obviously increased. There was no significant change in F_v/F_m, Φ_PSII, q_P, indicating stomatal limitation was the main reason why the photosynthesis of cotton reduced. P_n decreased slowly, while C_i began to rise and L_s began to decline under SRWC (45±5) % treatment for 14-49 days. F_v/F_m, Φ_PSII, q_P  decreased while NPQ rose first then declined, which indicated that non-stomatal limitation worked to reduce the cotton photosynthetic performance. The boll setting intensity reduced significantly and the number of boll and yield declined. The critical stress time of cotton growth in current study was 21 and 14 days respectively under SRWC (60±5) % and SRWC (45±5) % treatments during the flowering and boll-forming stage.