Abstract

The main natural source of organic carbon and nutrients into freshwater ecosystems are leaves which have fallen into the water. During the degradation process of leaf litter, many organic and inorganic substances are released, and, under certain conditions, they may aggregate to form humic substances. During the present investigation leaf litter degradation extracts (“new born” humic substances) from Fagus sylvatica (beech) and Quercus robur (oak) were produced, recreating natural leaf decomposition. The impact of leaf litter breakdown products on the antioxidative system and the intracellular hydrogen peroxide content of Nitellopsis obtusa was studied. This was done via Nitellopsis obtusa cells exposure for 2 h to leaf litter degradation extracts during up to a 30 day period. Significant (P<0.05) elevation of soluble glutathione S-transferase and glutathione reductase activity in N. obtusa treated with both extracts from Fagus sylvatica (beech) and Quercus robur (oak) were observed, while there were no statistically significant differences in intracellular hydrogen peroxide content and catalase activity. Results indicate that newly created humic substances (leaf litter degradation extracts) may be an important environmental factor affecting aquatic vegetation in freshwater systems. Keywords: Fagus sylvatica,