Legacy effects of altered flooding regimes on decomposition in a boreal floodplain

Abstract

Background and aims: Since long-term experiments are scarce, we have poor understanding of how changed flooding regimes affect processes such as litter decomposition. Methods: We simulated short- and long-term changed flooding regimes by transplanting turfs between low (frequently flooded) and high (in-frequently flooded) elevations on the river bank in 2000 (old turfs) and 2014 (young turfs). We tested how incubation elevation, turf origin and turf age affected decomposition of standard litter (tea) and four types of local litter. Results: For tea, we found that the initial decomposition rate (k) and stabilization (S) of labile material during the second decomposition phase were highest at high incubation elevation. We found intermediate values for k and S in young transplanted turfs, but turf origin was not important in old turfs. Local litter mass loss was generally highest at high incubation elevations, and effects of turf origin and turf age were litter-specific. Conclusion: We conclude that incubation elevation, i.e., the current flooding regime, was the most important factor driving decomposition. Soil origin (flooding history) affected decomposition of tea only in young turfs. Therefore, we expect that changes in flooding regimes predominantly affect decomposition directly, while indirect legacy effects are weaker and litter- or site-specific.