Effects of persistent water-table level drawdown on fine-root biomass and production in different site types of a boreal forested peatland

Purpose In peatlands, fine-root biomass (FRB) and production (FRP) and their depth distribution and plant functional type (PFT) composition are poorly known. We studied the effects of persistent water-table level drawdown on these characteristics in four forested boreal peatland site types that varied in soil nutrient and WTL regimes, ground vegetation and tree stand characteristics. Methods FRB was estimated by separating and visually identifying roots from soil cores extending down to 50-cm depth. FRP was estimated using ingrowth cores covering the same depth and the separated roots were identified using infrared spectroscopy. Results In both FRB and FRP, the differences between undrained and drained sites were small. In FRB, the clearest differences were seen in the originally wettest site, oligotrophic tall-sedge pine fen, and in the most-nutrient-rich site, herb-rich spruce swamp: in the pine fen FRB was smaller, and in the spruce swamp greater in the drained than in the undrained site. FRP was generally higher in nutrient-poor, pine-dominated sites. The depth distribution of FRB was more superficial than that of FRP, except for the most nutrient-rich spruce swamp. Tree and shrub roots dominated both FRB and FRP, except for the undrained pine fen, where graminoids and forbs dominated. Even there, these PFTs were replaced by trees and shrubs at the drained site. Conclusion Fine-root biomass and production vary widely both within and among different types of boreal forested peatlands. Lowering of WTL large enough to support greater-volume tree stands affects FRB and FRP relatively little.