Nitrification and denitrification in the rhizosphere of rice: the detection of processes by a new multi-channel electrode |
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| Authors: | I Arth P Frenzel |
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| Institution: | (1) Max-Planck-Institut für terrestrische Mikrobiologie, Karl von Frisch Strasse, 35043 Marburg, Germany e-mail: frenzel@mailer.uni-marburg.de Tel.: +49-6421-178821 Fax: +49-6421-178809, DE |
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| Abstract: | N turnover in flooded rice soils is characterized by a tight coupling between nitrification and denitrification. Nitrification
is restricted to the millimetre-thin oxic surface layer while denitrification occurs in the adjacent anoxic soil. However,
in planted rice soil O2 released from the rice roots may also support nitrification within the otherwise anoxic bulk soil. To locate root-associated
nitrification and denitrification we constructed a new multi-channel microelectrode that measures NH4
+, NO2
–, and NO3
– at the same point. Unfertilized, unplanted rice microcosms developed an oxic-anoxic interface with nitrification taking place
above and denitrification below ca. 1 mm depth. In unfertilized microcosms with rice plants, NH4
+, NO2
– and NO3
– could not be detected in the rhizosphere. Assimilation by the rice roots reduced the available N to a level where nitrification
and denitrification virtually could not occur. However, a few hours after injecting (NH4)2HPO4 or urea, a high nitrification activity could be detected in the surface layer of planted microcosms and in a depth of 20–30 mm
in the rooted soil. O2 concentrations of up to 150 μM were measured at the same depth, indicating O2 release from the rice roots. Nitrification occurred at a distance of 0–2 mm from the surface around individual roots, and
denitrification occurred at a distance of 1.5–5.0 mm. Addition of urea to the floodwater of planted rice microcosms stimulated
nitrification. Transpiration of the rice plants caused percolation of water resulting in a mass flow of NH4
+ towards the roots, thus supporting nitrification.
Received: 23 July 1999 |
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| Keywords: | Rice Nitrification Denitrification Rhizosphere Microelectrode |
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