The identification of abiotic stress by hydrogen peroxide concentration in submerged macrophyte tissues

Abstract

Submerged macrophytes in natural streams and stagnant waters are exposed to various abiotic stressors, including solar radiation, temperature fluctuations, and mechanical stress caused by water flow. During photosynthesis, carbohydrates are synthesized using electrons produced by absorbed solar radiation. However, surplus electrons, either due to excessive insufficient consumption, often caused by a lack of carbon dioxide (CO₂) or inorganic carbon, can generate reactive oxygen species (ROS), leading to an increase in hydrogen peroxide (H₂O₂) concentrations. Consequently, the intensity of these stressors is often measured by the concentration of H₂O₂ in plant tissues. It's important to note that H₂O₂ production is not necessarily linked to a single stressor but can result from a combination of environmental factors. The primary objective of the tests was to determine how Myriophyllum spicatum responds to stress and produces H₂O₂ in reaction to flow patterns in streams and to high photosynthetically active radiation (PAR) in stagnant water. Observations were made at six stream sites. At each site, the flow velocity of the unidirectional mean flow (MV) and the turbulence velocity (TV) were measured within M. spicatum patches. In stagnant water, observations were conducted both in a moat where M. spicatum patches were located and in outdoor experimental tanks, where the plants were grown under controlled water temperatures and natural sunlight. Myriophyllum spicatum samples were collected alongside PAR measurements, and the H₂O₂ concentration in plant leaves was analyzed using the TiSO₄ method. In streams, H₂O₂ concentrations were high in areas with very low turbulence. When turbulence reached sufficient levels, concentrations initially declined, then increased with further rising turbulence. In stagnant water, H₂O₂ concentrations, which were higher at elevated temperatures, increased proportionally with PAR intensity. In both scenarios, H₂O₂ levels decreased under extremely high stress, likely due to the deterioration of plant shoots. These results suggest that surplus electrons, arising from either limited electron consumption due to a restricted carbon source for synthesizing organic carbon or an excessive electron supply driven by strong PAR intensity, elevate H₂O₂ concentrations. However, with a sufficient carbon source available, H₂O₂ concentrations increase under heightened turbulence, likely as a result of mechanical stress.