Oxygen control prevents denitrifiers and barley plant roots from directly competing for nitrate |
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Authors: | Sø ren Christensen,James M. Tiedje |
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Affiliation: | Copenhagen University, Institute of Population Biology, Copenhagen, Denmark;Michigan State University, Dept. Crop and Soil Sciences Plant and Soil Sciences Building, East Lansing, MI, U.S.A. |
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Abstract: | Abstract Two denitrifying bacteria ( Pseudomonas chlororaphis and P. aureofaciens ) and a plant (barley, Hordeum vulgare ) were used to study the effect of O2 concentration on denitrification and NO3− uptake by roots under well-defined aeration conditions. Bacterial cells in the early stationary phase were kept in a chemostat vessel with vigorous stirring and thus a uniform O2 concentration in the solution. Both Pseudomonads lacked N2O reductase and so total denitrification could be directly measured as N2O production. Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O2 saturation (0.14 μM O2) and was totally inhibited at 0.04% O2 saturation (0.56 μM O2). In this well-mixed system denitrification was 10-times more oxygen sensitive than stated in earlier reports. Uptake of nitrate by plants was measured in the same system under light. The NO3− uptake rate decreased gradually from a maximum in 21% O2-saturated medium (air saturated) to zero at 1.6% O2 saturation (22.4 μM O2). Owing to the very different non-overlapping oxygen requirements of the two processes, direct competition for nitrate between plant roots and denitrifying bacteria cannot occur. |
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Keywords: | Pseudomonas chlororaphis Pseudomonas aureofaciens Competition Denitrification Oxygen Nitrogen |
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