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

Abstract

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 CH4 fluxes. This study sought to measure CH4 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 {beta}-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 CH4 emissions at the spruce site. Drainage improved soil aeration at the coastal cedar-hemlock site and reduced CH4 emission rates. Fertilization did not affect CH4 emissions from either site. CH4 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.