Impact of regulated water levels on willows (Salix subfragilis) at a flood-control dam, and the use of hydrogen peroxide as an indicator of environmental stress

摘要

Plants are subjected to various environmental stressors, both natural and artificial. Environmental stressors that lead to an excessive generation of reactive oxygen species (ROS) may adversely affect physiology and well-being of organisms. The amount of ROS, therefore, could potentially be used to quantify environmental stresses in plants. In this study, the effect of changes in the water levels and elevation at which plants are located was examined in the drawdown zone of a flood control dam (Miharu dam), located in Fukushima in northern Japan. The Salix subfragilis willows are an important plant species in the reservoir as these plants are resistant to prolonged submerged conditions and provide the most suitable habitat for the growth and reproduction of many aquatic organisms. S. subfragilis growing in the drawdown zone exhibited high mortality rates from 2008 to 2016. Leaf samples of S. subfragilis were collected in the drawdown zone at different elevations shortly after drawdown (June), and several months after drawdown (August and October). The samples were taken under light exposure; additionally, dark-adapted (30 min) samples were collected in order to evaluate photosystem-induced ROS generation. The mortality rate of S. subfragilis trees was abnormally high over the previous years, particularly at higher elevated sites. Foliar H2O2 concentrations were significantly increased in samples collected at August and October samples, compared to June samples. Catalase, ascorbate peroxidase, and guaiacol peroxidase activities were also increased, corresponding with the H2O2 content. No significant difference in H2O2 concentrations was found between samples from the lower edge of the drawdown zone and those collected at constantly inundated sites. The H2O2 concentration of light-and dark-treated samples indicated that there was no additional ROS accumulation due to photosynthesis. The results indicated that the high mortality of the trees was associated with long-term exposure to drought conditions due to the drawdown, although this was not confirmed by conventional monitoring. These findings support the use of H2O2 as an environmental stress indicator in vegetation management.