Environmental manipulation treatment effects on the reactivity of water-soluble phenolics in a subalpine tundra ecosystem

Subalpine tundra ecosystems are characterised by a multitude of ecological stresses such as nutrient poor conditions and low pH, and are dominated by plants producing high levels of phenolic compounds. The aim of this study was to assess how alleviation of those stresses affects the reactivity (oxidation and complexation) of water-soluble phenolics in plant tissue, humus and mineral soil. We used a field manipulation experiment that was set up in 1989 in which plots dominated by the ericacious dwarf shrub Empetrum hermaphroditum Hagerup have been subjected to additions of inorganic and organic nitrogen (N), charcoal, and lime. From these plots we collected senescent leaves of E. hermaphroditum, humus, and mineral soil and determined the levels of redox-active phenolics and complexation activity (e.g., complexation towards phenol, L-tryptophan, and proteins) in water extracts of those samples. Addition of charcoal to the soil increased redox-active phenolics in E. hermaphroditum senescent leaves while the other treatments had no significant effect. Most of the treatments did not significantly affect the levels of redox-active phenolics in the humus and mineral soil water extracts. However, inorganic N amendments slightly increased the concentration of redox-active phenolics in humus. There were strong positive effects of addition of inorganic and organic N on the complexation activity towards phenol, L-tryptophan and proteins in humus water extracts. In addition, charcoal amendments increased complexation towards proteins (measured as lipase activity). In general, our results show that environmental manipulation treatments can have differential effects on redox-active phenolics and complexation activity of phenolics present in senescent leaves and humus. This is important knowledge for a better understanding of how environmental changes can affect humification processes and N cycling.