Water Table Affects Root Production and Viability Differently Among Plant Functional Types in a Northern Peatland Mesocosm Study.

Fine roots of peatland plants play an important role in regulating biogeochemical cycles in nutrient-limited peatlands, impacting the production of the greenhouse gases methane and CO₂. The response of roots to water levels can impact vertical distribution of functional roots of differently among plant functional types. For example, ericaceous shrubs are typically have active roots above the saturated layer pf peat, while sedges and other graminoids have deep aerenchymous roots that transport oxygen below the water table to sustain root functioning. 

We manipulated water table levels in peat mesocosms to simulate drier climatic conditions, and measured root production across the growing season (May−Oct) in 2013 using monthly minirhizotron imaging alongside novel image processing approaches.  At the conclusion of the experiment, we harvested roots in 10-cm depth increments from the top 40 cm and estimated biomass of functional roots from each plant type using a rapid fluorescence assay to quantify cell viability. Results show that sedges, while a having lower aboveground biomass, had comparable amounts of root production compared to ericoid shrubs. Water table manipulations reduced root productivity of shrubs, but did not have a significant effect on sedge root production. Likewise, sedges had viable roots to below 40 cm soil depth and were not affected by lowered water tables, while ericoid shrubs had functional roots restricted to above the water table, and therefore had greater biomass of functional roots with lowered water tables.