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 (H 2 O 2 ) is relatively stable and can be measured accurately. Thus, for the quantification of submerged macrophyte species, H 2 O 2 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 H 2 O 2 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 H 2 O 2 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 H 2 O 2 concentration increased with higher salinity. A change in Chlorophyll a (Chl- a ) concentration is associated with an altering H 2 O 2 concentration, following a unique negative relationship with H 2 O 2 concentration. If H 2 O 2 exceeded 45 μmol/gFW, the homeostasis collapsed, and H 2 O 2 and Chl- a significantly declined afterward. The above findings indicate that H 2 O 2 has a negative effect on the physiological condition of the plant. The increase in H 2 O 2 concentration was prevented by antioxidant activities, which elevated with increasing H 2 O 2 concentration.