LI Ping, ZHANG Yong-Jiang, LIU Lian-Tao, SUN Hong-Chun, WANG Qi, LI Cun-Dong
The responses of leaf relative water content, leaf water potential, photosynthetic parameters, and chlorophyll fluorescence parameters were studied with different Bt transgenic cotton cultivars (Nongdamian 8 and Lumianyan 28) under five different water stresses: normal irrigation (CK), light stress (LS), middle stress (MS), severe stress (SS), and extreme stress (ES). The results showed that the growth of cotton seedlings was inhibited significantly. Water stress resulted in a progressive decrease in relative leaf water content, leaf water potential, net photosynthetic rate (Pn), light use efficiency (LUE), maximum photosynthesis efficiency of PS II(Fv/Fm), actual photosynthesis efficiency of PS II in light (φPS II), and photochemical quenching (QP). However, it led to an increase in the limiting value of stomata (Ls), water use efficiency (WUE), and non-photochemical quenching (NPQ). Overall, compared with CK, there were significant differences in Pn and NPQ between LS, MS, SS, and ES: from LS to ES, the average PN decreased by 11.5%, 18.1%, 32.1%, and 38.1%, respectively, whereas NPQ increased by 24.1%, 50.9%, 79.4%, and 145.1%, respectively. The experiments indicated that LS had little effect on photosynthetic characteristics during the cotton seedling stage, but greater water stress (higher than MS) resulted in the decline of photosynthetic capacity and photoinhibition of PS II.
