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

Abstract

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.