Growth and physiological responses of Scirpus mariqueter to extremely high temperatures.

Extreme weather events are becoming more and more frequent in the context of global climate change, but we know little about the responses of salt marsh plants to extreme weather conditions. In this study, a 7-day controlled greenhouse experiment was conducted to investigate the response of growth, physiology and photosynthetic parameters of Scirpus mariqueter, a typical estuary salt marsh plant species, to extremely high temperatures (40, 45, 50 ?). Results showed that high temperature (45-50 ?) significantly enhanced the root to shoot ratio of S. mariqueter and that more biomass was allocated to underground to cope with the damage induced by the high temperature. The content of chlorophyll a, chlorophyll b and total chlorophyll decreased with the increases of temperature, indicating that high temperature inhibited the synthesis of chlorophylls. High temperature stress affected the physiology of S. mariqueter, malondialdehyde content in leaves and roots decreased significantly when exposed to high temperature (45-50 ?), which indicates that S. mariqueter has a certain heat tolerance. The content of proline was significantly higher in high temperature treatment (40-50 ?) than in control, soluble sugar content decreased significantly in leaves and increased in roots, suggesting that the osmotic adjustment substances produced by S. mariqueter were active in resisting stress. Compared with that in control, net photosynthesis rate of S. mariqueter increased at 40 ?, but decreased significantly at 45 and 50 ?, accompanied by the decreases of stomatal conductivity, intercellular CO₂concentration, transpiration rate, and water use efficiency, suggesting that photosynthesis rate of S. mariqueter can be promoted under a certain range of high temperature but be inhibited under extremely high temperature. Stomatal restriction was found to be the major limiting factor. Our results can provide a reference for understanding the adaptation mechanism of salt marsh plants to extremely high temperature in the context of climate change.