We estimated fine-root biomass (FRB) and production (FRP) and their depth distribution and plant functional type (PFT) composition in four forested boreal peatland site types that varied in soil nutrient and water-table level regimes, ground vegetation and tree stand characteristics. Two were pine-dominated nutrient-poor sites (dwarf-shrub pine bog, tall-sedge pine fen) and two spruce-dominated nutrient-rich sites (Vaccinium myrtillus spruce swamp, herb-rich hardwood-spruce swamp). Measurements were done in two sites per site type: one undrained site and one site that had been drained for forestry. In each of the eight sites, we established three measurement plots. FRB was estimated by separating and visually identifying roots from soil cores extending down to 50-cm depth. The cores were taken in late August, 2016. FRP was estimated using ingrowth cores covering the same depth, and the separated roots were identified using Fourier transform infrared spectroscopy (FTIR). The ingrowth cores were incubated for two years, starting in November 2015 and ending in November 2017. Tree-stand basal area and stem volume per species, and projection cover of ground vegetation per species were determined in summer 2018. We monitored the soil water-table level and soil temperatures in 5 and 30 cm depths with dataloggers. Soil pH, bulk density, and carbon, nitrogen, phosphorus, potassium, calcium, magnesium, iron, manganese, boron, zinc, and copper concentrations were measured from peat cores extending down to 50-cm depth and taken simultaneously with the FRB cores. FRB, FRP and peat properties are presented for 10-cm depth segments. FRB, FRP and peat properties are presented for 10-cm depth segments. Peat cores were taken with a box-shaped 65 mm x 37 mm peat corer, except in the wet TP site where a 60 mm x 60 mm corer was used.

Site types: DP: Dwarf-shrub pine bog (Finnish name isovarpuräme); TP: Tall-sedge pine fen (varsinainen sararäme); VS: Vaccinium myrtillus spruce swamp (mustikkakorpi); HS: herb-rich hardwood-spruce swamp (ruohokorpi); classification follows Laine et al. (2012) Suotyypit ja turvekankaat - opas kasvupaikkojen tunnistamiseen. Metsäkustannus, Helsinki. 160 p., site types described also in Laine et al. (2004) Lakkasuo - a guide to mire ecosystem. University of Helsinki Department of Forest Ecology publications 31: 1-123.Ingrowth cores were prepared as in Laiho et al. (2014; doi:10.1007/s11104-014-2225-3) and Bhuiyan et al. (2018; doi:10.1007/s11104-016-3070-3) and filled with root-free peat: non-fertilized horticultural Sphagnum peat for the nutrient-poor DP sites (bogs), sedge peat from a site representing the same site type for TP sites (fens), and dark swamp peat for the VS and HS sites (swamps).