Plant and Soil

, Volume 290, Issue 1–2, pp 245–257

NH4+ triggers the synthesis and release of biological nitrification inhibition compounds in Brachiaria humidicola roots

  • G. V. Subbarao
  • H. Y. Wang
  • O. Ito
  • K. Nakahara
  • W. L. Berry
Original Paper

DOI: 10.1007/s11104-006-9156-6

Cite this article as:
Subbarao, G.V., Wang, H.Y., Ito, O. et al. Plant Soil (2007) 290: 245. doi:10.1007/s11104-006-9156-6

Abstract

The release of chemical compounds from plant roots that suppress soil nitrification is termed biological nitrification inhibition (BNI). Determining the environmental factors that control the synthesis and release of BNI-compounds from Brachiaria humidicola (Rendle) Schweick, a tropical pasture grass that thrives on acid soils, is the focus of this investigation. Because the BNI trait is related to the N status of the plant, we investigated the possibility that the expression of this trait would be related to the forms of N found in the root environment. Plants were grown with two sources of N, NH4+ or NO3 for 60 days and the release of BNI-compounds monitored. Only plants grown with NH4+ released BNI-compounds from roots. The presence of NH4+ and possibly the secondary effect of its uptake (i.e., acidic pH) in the root environment significantly enhanced the release of BNI-compounds. Both the NH4+ and NO3 grown plants responded to the stimulus from NH4+ in the root environment. BNI-compounds found in root tissue and their release were nearly three times greater in NH4+ grown than from NO3 grown plants. The BNI-compounds released from roots composed of at least three active components—Type-I (stable to pH changes from 3.0 to 10), Type-II (temporarily loses its inhibitory effect at a pH higher than a threshold pH of 4.5 and the inhibitory effect is reestablished when the root exudate pH is adjusted to <4.5) and Type-III (inhibitory effect is irreversibly lost if the pH of the root exudate reaches 10.0 or above). A major portion of BNI-compounds released in the presence of NH4+ is of Type-I. In the absence of NH4+, mostly Type-II and Type-III BNI-compounds were released. The BNI-compounds inhibited the function of Nitrosomonas europaea through the blocking of both ammonia monooxygenase and hydroxylamino oxidoreductase pathways. These results indicate that the release of BNI-compounds from B. humidicola roots is a regulated function and that presence of NH4+ in the root environment is necessary for the sustained synthesis and release of BNI.

Keywords

Biological nitrification inhibition BNI-compounds Bioluminescence assay Nitrogen forms 

Copyright information

© Springer Science+Business Media B.V. 2006

Authors and Affiliations

  • G. V. Subbarao
    • 1
  • H. Y. Wang
    • 2
  • O. Ito
    • 1
  • K. Nakahara
    • 3
  • W. L. Berry
    • 4
  1. 1.Crop Production and Environment DivisionJapan International Research Center for Agricultural Sciences (JIRCAS)IbarakiJapan
  2. 2.The State Key Laboratory of Soil and Sustainable AgricultureNanjingChina
  3. 3.Food Science and Technology DivisionJapan International Research Center for Agricultural Sciences (JIRCAS)IbarakiJapan
  4. 4.Department of Ecology and Evolutionary BiologyUniversity of CaliforniaLos AngelesUSA

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