REDUCING EMISSIONS OF THE GREENHOUSE GAS NITROUS OXIDE (N₂O) BY ISOLATED BACTERIA STRAINS FROM WHEAT RHIZOSPHERE

Microbial dissimilatory nitrogen metabolism processes are among the main factors negatively affecting nitrogen availability to plants. These include nitrate respiration and denitrification, which result in reduction of plant-available N and emission of N₂O, a highly potent greenhouse gas. These activities are strongly enriched in the rhizosphere, stressing the environmental and agricultural importance. One approach to minimize these effects is plant inoculation by active N₂O reducing bacteria and thus minimizing N₂O emissions.

In this study, bacteria were isolated from wheat roots grown in two different soil types (e.g. clay and sandy loam soils) under ambient and elevated CO₂ atmospheric levels. The procedure included isolation of bacteria under anaerobic atmosphere, enriched with N₂O gas, in the presence and absence of nitrate source. The bacteria that have grown faster in absence of oxygen and nitrate (where N₂O was the sole oxidized nitrogen electron acceptor) compared to their growth in the presence of nitrate, were selected for further experiments. All together five promising isolates were tested while only one of them, representative of Alcaligenes faecalis sp., has shown high N₂O reduction ability rather than nitrate reduction. Bacterial community structure analyses of wheat roots grown at ambient CO₂ atmospheric level revealed that bacteria of the family Alcaligenaceae is present at a very low level (~0.1%). The next step in this research is inoculation of wheat plants with the A. faecalis isolate to validate the possibility to reduce N₂O emission under condition simulating agricultural field.