Short term grazing increased growing-season N2O production and decreased its reduction potential by reducing the abundance and expression of nosZ clade II gene in a semi-arid steppe

Abstract

Understanding nitrous oxide (N₂O) production as well as reduction in response to grazing and mowing is essential for designing better management strategies to improve sustainability of grassland ecosystems. We evaluated how four years of grazing or mowing altered N₂O production and reduction potential, gene abundance, and expression of microbial functional groups pertinent to N₂O production in situ on a typical grassland in Inner Mongolia. In our study, we found that grazing dramatically raised soil ammonium (NH₄⁺-N) and nitrate (NO₃^--N) concentrations, AOB gene abundance and potential of N₂O production through nitrification (N_N2O) and denitrification (D_N2O) in summer, but lessened the expression of nosZ clade II gene in all seasons. Mowing had minor effect on soil inorganic nitrogen (N) concentrations. Mowing diminished the quantity of denitrification genes (narG and nosZ), expression of nosZ and nosZ clade II genes, and D_N2O concentration. The expression and abundance of nosZ clade II gene were related to D_N2. These results suggested that short-term grazing could enhance N₂O production potential in peak growing season, while the reduction in abundance and expression of nosZ calde II gene might be an important contributor to the enhanced N₂O production of semi-arid typical steppe grasslands.

Keywords: Denitrification; Nitrification; Nitrous oxide; Reduction; mRNA.