Short-Term Soil Waterlogging Improves Cotton Tolerance to High Temperature by Triggering Antioxidant Defence System in Cotton Seedlings

Soil waterlogging and high temperature (HT) are serious abiotic stresses that negatively affect cotton growth and yield. Yet effects of prewaterlogging to HT subsequently in cotton seedlings have not been obtained. To address this, two temperature conditions (30/20°C and 35/25°C) and two soil waterlogging levels (0 and 3 days) were established during the cotton seedling stage. Results showed that indexes of plant performance were decreased markedly under HT. Unexpectedly, plant performance for the treatment of HT combined with 3 days of soil waterlogging (HW) was better than HT treatment (specifically, increase of 7.9%, 9.0%, 10.2%, 5.4% and 4.6% in leaf area, plant height, belowground biomass, aboveground biomass and root-to-shoot ratio was detected). Decreases in MDA (malondialdehyde), H₂O₂ (hydrogen peroxide) contents and $O_2^{-}$ (superoxide radicals) generation rate under HW treatment were observed by 14.1%, 7.7% and 14.1%, respectively, compared with HT. Moreover, ASA (ascorbic acid) content and DHAR (dehydroascorbate reductase) activity were improved by 19.7% and 13.8% for HW treatment relative to HT, however, the opposite situation for activities of APX (ascorbate peroxidase) and GR (glutathione reductase). Besides, activities of SOD (superoxide dismutase), CAT (catalase) and POD (peroxidase) in HW treatment were increased by 16.7%, 8.3% and 18.4%, separately. Thus, we concluded that short-term soil waterlogging improved cotton cross-tolerance to the continued high-HT stress by enhanced SOD, CAT, POD and DHAR activities, increased ASA content in cotton seedlings. These results were expected to provide a theoretical basis for understanding cotton's cross-tolerance to abiotic stress.