Linking Root Productivity and Rhizosphere Processes of Different Plant Functional Types to Biogeochemical Processes in Northern Peatlands.

Fine roots of peatland plants play an important role in regulating biogeochemical cycles in nutrient-limited peatlands, impacting the production of the greenhouse gases (GHG) methane and CO₂. The response of belowground productivity to water levels can impact vertical root distribution of plant functional types differently. Ericaceous shrubs are shallow-rooted, with long-lived mycorrhizal roots; in contrast, sedges and other graminoids have deeper roots that develop aerenchyma and transport oxygen below the water table to sustain root functioning.  Radial oxygen loss from aerenchymous roots can change oxidation-reduction potential of the rhizosphere, and impact C cycling pathways and the ratio of methane to CO₂ production.

Using mesocosms and root windows, we sought to quantify the root and rhizosphere dynamics of three peatland plant community types consisting of either unmanipulated plots containing both ericaceous shrubs and graminoids, plots with only ericaceous shrubs, or plots with only graminoids. We evaluated the impacts of high and low water tables and plant community type   to investigate the impacts on root dynamics, belowground gas bubble production, and methane and CO₂ fluxes. Root production and gas bubble area were quantified using minirhizotrons down to 45 cm below the peat surface, while efflux of methane and CO₂ were quantified using static chambers. Using root windows, planar optode sensors were used to visualize the increase in fine-scale rhizosphere oxygen concentrations below the water table from sedge roots. Results from these studies show that both water table levels and plant functional type effect vertical distribution of root production and GHG fluxes, while rhizosphere oxygenation resulting from graminoid roots likely has important consequences for belowground C cycling pathways.