Effect of mounding, drainage and fertilization on CH4 fluxes and methane-cycling functional genes in waterlogged forest stands

Site preparation techniques including mounding, drainage and nitrogen (N) fertilization can enhance seedling survival and site productivity, particularly in waterlogged, low-productivity forest stands. However, practices that alter soil conditions and site hydrology can lead to the unintended alteration of biogeochemical process rates, such as CH 4 fluxes. This study sought to measure CH 4 fluxes measured using static closed chambers at a sub-boreal spruce site and a coastal cedar-hemlock site that underwent mounding and drainage, respectively, to manipulate water table depth relative to planted seedlings, as well as fertilization. The abundance of methyl coenzyme M reductase ( mcrA ) gene found in methanogenic archaea and the particulate methane monooxygenase ( pmoA ) gene found in methane-oxidizing bacteria (MOB) were examined. The use of sulphate as a potential method to stimulate sulphate-reducing bacteria (SRB) and reduce methanogen activity was also investigated using the dissimilatory sulfite reductase β-subunit ( dsrB ) gene. qPCR was used to link mcrA,pmoA and dsrB gene abundance to soil factors and GHG fluxes. Mounding created hot-spots of CH 4 emissions at the spruce site. Drainage improved soil aeration at the coastal cedar-hemlock site and reduced CH 4 emission rates. Fertilization did not affect CH 4 emissions from either site. CH 4 rates were influenced by soil water content and mcrA abundance. Measurements of microbial functional genes can elucidate the effects of site preparation on GHG fluxes in waterlogged forest stands.