Yitzhak Hadar  -Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem

Nitrous oxide (N₂O) is a greenhouse gas and a potent ozone-depleting substance in the stratosphere. Agricultural soils are one of the main global sources of N₂O emissions, particularly from cereal fields due to their high areal coverage. The aim of this study was to isolate N₂O-reducing bacteria able to mitigate N₂O emissions from the soil after inoculation. We isolated several bacteria from wheat roots that were capable of N₂O reduction in vitro and studied their genetic potential and activity under different environmental conditions. Three of these isolates- all carrying the nitrous oxide reductase-encoding clade I nosZ, able to reduce N₂O in vitro, and efficient colonizers of wheat roots- presented different N₂O-reduction strategies when growing in the root zone, possibly due to the different conditions in situ and their metabolic preferences. Each isolate seemed to prefer to operate at different altered oxygen levels. Isolate AU243 (related to Agrobacterium/Rhizobium) could reduce both nitrate and N₂O and operated better at lower oxygen levels. Isolate AU14 (related to Alcaligenes faecalis), lacking nitrate reductases, operated better under less anoxic conditions. Isolate NT128 (related to Pseudomonas stutzeri) caused slightly increased N₂O emissions under both anoxic and ambient conditions. These results therefore emphasize the importance of a deep understanding of soil–plant–microbe interactions when environmental application is being considered.