Interactive effects of solar UV-B-radiation and nutrient supply on the formation and detoxification of oxidative stress and its consequences to growth of green marine macroalgae

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The eutrophication of coastal ecosystems resulting from anthropogenic land-use is an increasingly growing problem worldwide. Thus, the rapid growth of opportunistic green macroalgae is promoted, which can lead under appropriate environmental conditions to large macroalgal blooms. In contrast, disproportionately high solar ultraviolet B (UV-B) radiation in the hydrosphere, which increases locally and seasonally as a consequence of anthropogenic stratospheric ozone depletion, impairs macroalgal growth significantly. The aim of this research is to characterize the interactive effects between the two antagonistic environmental factors in spatial and temporal resolution and to elucidate the underlying physiological mechanisms. A bloom-forming green macroalga of the genus Ulva is intended to serve as a model organism. The impact of nitrogen assimilation on the formation and detoxification of reactive oxygen species (ROS) is the central subject of the investigation. The resulting implications for the growth of the macroalga can provide explanations for its survival under adverse conditions in the field. The competition between nitrogen assimilation and the Mehler reaction for electrons, which originate from the photosynthetic electron transport, is investigated in physiological laboratory studies. The potential of nitrogen assimilation in order to avoid UV-B-induced oxidative stress is the main subject of these studies. To understand these processes under natural conditions, UV-B-experiments are conducted in relation to the seasonally fluctuating nitrogen availability. Furthermore, the impact of different inorganic nitrogen histories on macroalgal oxidative stress caused by high summer UV-B-radiation is thoroughly investigated under field conditions in Ulva sp.