| Soilless-substrate naked-seedling and transplanting, a simplified high-yielding and high quality cotton cultivation technology, adjusts to the development of modern agriculture, and therefore has become the main simplified cotton cultivation technology in China. Two experiments were designed in this study according to two key factors (water and temperature) influencing cotton growth. The first experiment was conducted to study the variation rules of leaf shape and support theoretical basis for industrial seedling nursery. Bare-root seedlings with consistent age were gradually dehydrated and rehydrated in illumination incubator. 13 dehydration treatments with 3 replications were included in this experiment:dehydrated for 0h,2h,4h,6h,8h,12h,24h,36h,48h,12h followed by rehydrated for 2h,24h followed by rehydrated for 2h, 36h followed by rehydrated for 2h,dehydrated for 48h followed by rehydrated for 2h. The second experiment was conducted to investigate the effects of temperature on physiological and biochemical indices during recovering stage. The temperature differences were achieved by using 3 cultivation technologies: open cultivation, film-mulched and plastic tunnel in film-mulched. Field experiment was designed as a randomized blocks with 3 replications. Adjusting osmotic substances, antioxidant enzyme activities and several morphological indicators were determined. Results of the first experiment:(1)Relative water content in leaves gradually decreased with increasing time under water stress. The effect of 2 hours'rehydration was obvious for 12 hours'dehydration and was diminished with extended dehydration time. For untreated leaves, stomata were open and convex; no strip was occurred on the cell surface, and cells can be distinguished clearly with obvious intercellular gaps. With increased time and degree of dehydration, stomata gradually closed and turned to subside from convex. Moreover, the cells shrink and intercellular gaps were less clear. 2 hours'rehydration resulted in swelled epidemic cells due to imbibing water (cell shrink was broken); however the stomata were not turned to open.(2)Compared with untreated, MDA content of root and leaf and Pro content of leaf in dehydration treatments were obviously increased. Especially, MDA content in root and Pro content in leaf are similar in variation trends, which increased slowly in the early stage, and then sharp increase occurred, but different in the turning point(one is 12h, and the other is 24h). 2 hours'rehydration can reduce MDA content in root to a low level, while only small effect in leaves was observed. MDA content in root is lower than that in leaves.(3)In the whole dehydration process, activities of antioxidant protection enzymes, including SOD, CAT and POD, tended to rise with the increased degree of water stress, but the effect of rehydrated for 2h is not obvious. SOD activity showed sharp increase from 12h to 24h. POD activity changed slowly before 12h dehydration and changed sharply afterwards. It is concluded that transplanted cotton seedlings can survive if rehydration promptly after less than 24h dehydration in the cotton seedlings transplant season. Results of the second experiment:(4)There was no significant difference in chlorophyll content of cotton seedling between different temperature treatments. MDA and proline content were all going up at first, and then descending with growing process. The contents of MDA and proline with respect to film-mulched and plastic tunnel in film-mulched treatment were lower than those with respect to open cultivation treatment. Higher temperature is in favor of relieving the environment stress to cotton seedling.(5)SOD and POD activities were all going up in early recovering stage for three different treatments. In late stages, SOD and POD activities for 3 treatments fit the relationship below: open> film mulching>plastic tunnel in film-mulching. POD was more sensitive to the stress environment than SOD.(6)Three treatments showed the same variation trends in root vigor (decline, increase and then decline), but different in the time of turning point. In recovering stage, there was no significant difference in cotton seedling qualities among treatments; however, after recovering stage, the fresh weight and leaf area per plant for plastic tunnel in film-mulched cotton were greater than the other two treatments. The results showed that: Higher temperature is beneficial to shorting the recovering stage and promoting the cotton seedling delivery early.
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