Peatland ditching as a driver of dissolved organic matter mobilization - the role of fungal communities

Ditching of peatlands has been used extensively in Scandinavia with the purpose to promote tree growth. Studies show that concentrations of dissolved organic matter (DOM) are higher in waters exported from ditched peatlands compared to pristine systems, suggesting that ditching may contribute to browning observed in surface waters in forested regions.

After ditching and when trees are established, the peat will be colonized by ectomycorrhizal (EM) fungi, which supply the trees with nutrients. We hypothesize that EM-fungi will mobilize DOM to the soil water while mining the peat for nutrients and saprotrophic fungi will become more active when the peat gets aerated, which will also result in mobilization of DOM. In the current project we are exploring the link between fungal communities and DOM mobilization in a peatland gradient, spanning from pristine conditions with high water level and lack of trees, to strongly drained conditions with low water level and established pine forest. Along this gradient, soil water was sampled from ground water tubes. Water and peat samples were analyzed for organic matter concentrations and the fungal community was characterized by metabarcoding.

DOM concentrations in the soil water were increasing towards the ditch - where the water level was lower and the tree growth higher - as was the fungal biomass. While these results are in line with our hypothesis, the results on fungal community composition will provide important information to assess the link between fungal processes and DOM mobilization.

This study will bring much needed information on succession of fungal communities with different decomposition strategies along peatland ditching gradients and potential links to DOM mobilization and surface water browning.