Peatland Vegetation Patterns in a Long Term Global Change Experiment Find no Reflection in Belowground Extracellular Enzyme Activities

Abstract

To assess the effects of global change on peatland vegetation and biogeochemistry we used a long term (21 years) in-situ plot scale manipulation experiment comprising nitrogen (N; ambient and 30 kg ha−1 yr−1), temperature (T; ambient and + 3.6 °C during growing season) and sulfur (S; ambient and 20 kg ha−1 yr−1) treatments in an oligotrophic boreal peatland. Vegetation was assessed by plant species cover estimates, while biogeochemical processes were characterized by measuring potential extracellular enzyme activity (EEA) of glucosidase, cellulase, aminopeptidase, phosphatase, and sulfatase in the peat matrix. We hypothesized that the plant communities would change in response to the N and T manipulations, and that belowground EEA would respond distinctively to the applied treatments as well as to changes in plant community. We found vascular plant cover to have strongly increased in the T treatment, whereas the Sphagnum cover collapsed in the high N treatment. Belowground we found enhanced enzymatic C and N acquisition activity in response to the N treatment, but EEA showed no response to the T treatment. No S effects were found, neither aboveground nor belowground. Contrary to our expectations, our data reveal a mismatch between above-ground vegetation patterns and belowground decomposition processes. In particular, the large increase in vascular plant cover in the warming treatment found no reflection in belowground EEA.