Microbial functional groups involved in greenhouse gas fluxes following site preparation and fertilization of wet low-productivity forest ecosystems

Forest site preparation and fertilization can improve stand productivity, but can alter the efflux rates of greenhouse gases (GHGs), CO2, CH4 and N2O, from wet soils. This study investigated the effects of these management practices on GHG fluxes (using static closed chambers), soil physico-chemical parameters, microbial community structure (using terminal-restriction fragment length polymorphism (TRFLP) of bacterial 16S and fungal ITS targets) and microbial functional group abundance (methanogens, methanotrophs, nitrifiers, denitrifiers, sulphate-reducing bacteria, using quantitative PCR) in both forest floor and mineral soils. The research took place in British Columbia (BC), Canada, at the Aleza Lake Research Forest (ALRF), near Prince George, in a hybrid spruce stand subject to mounding and at the Suquash Drainage Trial (SDT) site near Port McNeill, Vancouver Island, in a western redcedar‒western hemlock‒yellow cedar stand subject to drainage. Mounding reduced CO2 fluxes and carbon (C) concentrations, but created anaerobic hot-spots of CH4 and N2O fluxes. Ditch drainage increased soil C about 20% after 15 years and did not affect respiration rates, though CH4 fluxes were reduced. Fertilization transiently increased N2O fluxes up to a maximum of 209 µg m-2 h-1, two months following fertilization. Bacterial and fungal T-RFLP profiles showed distinct patterns based on soil layer, and were altered by mounding, drainage and fertilization. Up to 84.4% of variation in CO2 emissions could be explained, with almost 50% of explained variation allocated to soil temperature. CH4 flux variation was explained by soil water content, soil temperature, methanogen (mcrA) and methanotroph (pmoA) functional gene abundance. Variation in N2O fluxes were significantly explained by soil water content, soil pH, NH4-N concentration, AOB amoA, nitrate reductase (narG) gene and nirSK gene abundance. In addition to denitrification genes, these data highlight AOB as important determinants of denitrification either by mediating nitrification or by direct nitrifier denitrification. This study elucidates the influence of different microbial functional groups on GHG flux rates in forest ecosystems.Forestry, Faculty ofGraduat