Elevated Temperature during Seedling Stage in Different Maize Varieties: Effect on Seedling Growth and Leaf Physiological Characteristics

Due to climate change, extreme high temperature weather is occurred frequently, which may cause a serious decline in crop yield. The growth status of maize seedlings directly affects the formation of later yield. However, there are insufficient understanding and studies on the maize seedling growth and physiological characteristics of leaves under high temperature stress at present. Hence, this experiment was designed to investigate the effects of heat stress on the plant biomass, photosynthetic characteristics, antioxidant enzyme activities and osmotic adjustment substances in the two maize varieties (heat-resistant variety ZD958 and heat-sensitive variety HSV20), with its clear the response mechanism of heat stress to the physiological metabolism changes at seedling stage. The results showed that the plant height increased, while the photosynthetic green leaf area, dry matter accumulation, root surface area and total root length significantly decreased under heat stress. High temperature treatment reduced the Pn, Gs, Tr, Fv/Fm, Fv/F0, qP and SPAD, and increased the Ci and NPQ. As heat stress time increased, the antioxidant enzyme activities first increased and then decreased, while the MDA content continued to increase. Additionally, the free proline content first increased and then decreased. Comparatively, we revealed that ZD958 has stronger antioxidant enzyme activities and osmotic regulation abilities, stable chlorophyll content, higher photosynthetic rate and maximal photochemical efficiency under heat stress, which may be the reasons why the root and shoot growth of seedlings has slighter changes and greater adaptability to heat stress.