Tannins can slow-down but also speed-up soil enzymatic activity in boreal forest

- Tannins can directly decrease but also increase enzymatic activity.
- Extent to which tannins modified activity is enzyme-specific.
- Mechanically, tannins affect enzyme conformation resulting in changes of activity.
- Tannin-enzyme complexes can exert residual activity.
- Enzyme inhibition/acceleration was observed also in soil studies.

The boreal forest ecosystem stores substantial amounts of soil organic matter (SOM), which may act either as a source or as a sink for atmospheric CO2 under climate change and that is why enzymatic SOM degradation is gaining increasing attention. The boreal forest ecosystem is rich in plant secondary compounds and in particular tannins which are seen as enzyme inhibitors. We studied changes in enzymatic activity after the addition of tannins. Our experimental design combined direct studies of the tannin effects on enzymes with laboratory soil mesocosm experiments. Our results showed that the addition of tannins directly led to both decreases and increases in the catalytic activity of enzymes, however, some differences between enzymes were observed. Overall, low concentrations of tannins increased the coiled structures of the enzymes boosting their catalytic activity. High concentrations of tannins acted in the opposite way, thereby diminishing the catalytic activity. We observed that tannins caused a similar change in enzymatic activity in soil mesocosm experiments. Tannin-enzyme synergy needs more study as these interactions can potentially play an important role in SOM decomposition of future climate, especially in the tannin-rich ecosystems.