The distribution of submerged macrophytes in response to intense solar radiation and salinity reveals hydrogen peroxide as an abiotic stress indicator.

The feasible condition for submerged macrophyte growth is hard to understand as many environmental factors contribute to establishing macrophyte distribution with different intensities generating excess reactive oxygen species (ROS). Among various kinds of ROS, hydrogen peroxide (H2O2) is relatively stable and can be measured accurately. Thus, for the quantification of submerged macrophyte species, H2O2 can be used to evaluate their distribution in a lake. Submerged macrophytes, such as Potamogeton anguillanus, were abundant in Lake Shinji. The largest biomass distribution was around 1.35 m deep, under low solar radiation intensity, and nearly no biomass was found less than 0.3 m deep, where solar radiation was high. Tissue H2O2 concentrations varied in response to the diurnal photosynthetically active radiation (PAR) intensity, which was followed by antioxidant activities, though slightly delayed. Laboratory experiments were conducted with different PAR intensities or salinity concentrations. A stable level of H2O2 was maintained up to about 200 µmol m-2 s-1 of PAR for 30 days, followed by a gradual increase as PAR increased. The H2O2 concentration increased with higher salinity. A change in Chlorophyll a (Chl-a) concentration is associated with an altering H2O2 concentration, following a unique negative relationship with H2O2 concentration. If H2O2 exceeded 45 µmol/gFW, the homeostasis collapsed, and H2O2 and Chl-a significantly declined afterward. The above findings indicate that H2O2 has a negative effect on the physiological condition of the plant. The increase in H2O2 concentration was prevented by antioxidant activities, which elevated with increasing H2O2 concentration.

Measurement of foliar H2O2 concentration can be an indicator of riparian vegetation management.

Riparian vegetation is frequently exposed to abiotic stress, which generates reactive oxygen species (ROS) caused by strong differences in a river's hydrological conditions. Among different ROS, hydrogen peroxide (H2O2) is relatively steady and can be measured appropriately. Thus, the quantification of plant H2O2 can be used as a stress indicator for riparian vegetation management. The current study examines the spatial distribution of plants by riparian vegetation communities across the elevation gradient of riparian zones through quantification of environmental stress using foliar H2O2 concentration. The trees Salix spp., Robinia pseudoacacia, Ailanthus altissima with Juglans mandshurica, and the herbs Phragmites australis, Phragmites japonica, and Miscanthus sacchariflorus were selected for this study. Leaf tissues were collected to analyze H2O2 concentration, meanwhile riparian soil was sampled to measure total nitrogen (TN), total phosphorus (TP), and moisture content. The H2O2 concentration of tree species increased with higher soil moisture content, which was negatively correlated for Salix and herb spp., in which H2O2 concentration always decreased with high soil moisture. In this study, we found a unique significant interaction between soil moisture content and H2O2 concentration, both positively or negatively correlated relationships, when compared with other parameters, such as TN or TP concentrations or TN: TP in riparian soil. The species-specific distribution zones can be explained by the H2O2 concentration in the plant for gravelly and sandy channels on a theoretical range of soil moisture. Each species' H2O2 concentration was estimated through derived equations and is directly related to an elevation above the channel. The comparison with the observed distribution of plant elevations in the field indicated that all species showed a spatial distribution that acts as species-specific elevations where H2O2 concentrations stayed below 40 µmol/gFW. Hence, the present study suggests that foliar H2O2 concentration can be a useful benchmark for the distribution potentiality of riparian vegetation.

Evaluation of Habitat Preferences of Invasive Macrophyte Egeria densa in Different Channel Slopes Using Hydrogen Peroxide as an Indicator.

Egeria densa is an often-found invasive species in Japan, which has spread widely in the past two decades in rivers where no macrophytes had previously been found. As a result, these ecosystems have now become dominated by E. densa. The habitat preference for E. densa colony formation was investigated using the tissue concentrations of hydrogen peroxide (H2O2: a reactive oxygen species) under varying conditions in rivers and laboratory conditions. The empirical equations that can describe the macrophyte tissue H2O2 formation under various velocity and light conditions were produced. The H2O2 concentrations of dark-adapted plants are proportional to the flow velocity, and the surplus H2O2 concentration in the light-exposed condition corresponded to the photosystems produced H2O2. When the H2O2 concentration exceeds 16 µmol/gFW, plant tissue starts to deteriorate, and biomass declines, indicating the critical values required for long-term survival of the plant. The empirically obtained relationships between flow velocity or light intensity and the analysis of H2O2 concentration for different slopes and depths of channels found that the H2O2 value exceeds the critical H2O2 concentration in channels with above 1/100 at around 0.6 m depth. This agrees with the observed results where colonies were not found in channels with slopes exceeding 1/100, and biomass concentration was the largest at depths of 0.6 to 0.8 m. H2O2 concentration is quite applicable to understanding the macrophyte condition in various kinds of macrophyte management.