Decomposing leaf litter: the effect of allochthonous degradation products on the antioxidant fitness and photosynthesis of Vesicularia dubyana.
Leaf litter is one of the major input sources of organic carbon and nutrients in freshwater ecosystems. Throughout the degradation and leaching of leaf litter in freshwater bodies, "new born" substances are continuously generated and may aggregate to form humic substances (HS). Although the effect of HS on the stress physiology of aquatic macrophytes has been case of several investigations, the effect of these "new born" compounds (leaf litter breakdown products) on the stress physiology of aquatic plants has not been studied yet. Our results show that leaf litter degradation extracts (LLDEs) from oak, beech, and mixed oak and beech leaves have deleterious effects on the physiology of the aquatic bryophyte Vesicularia dubyana, decreasing photosynthetic activity and enhancing oxidative stress response. These findings suggest that leaf litter degradation extracts may be an important environmental factor influencing community structure within freshwater ecosystems.