AOBPreview originally published online on July 15, 2005
Annals of Botany 2005 96(4):639-646; doi:10.1093/aob/mci216
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The Potential for Nitrification and Nitrate Uptake in the Rhizosphere of Wetland Plants: A Modelling Study
1 National Soil Resources Institute, Cranfield University, Silsoe, Beds MK45 4DT, UK and 2 Department of Life Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada
* For correspondence. E-mail g.kirk{at}cranfield.ac.uk
Received: 18 October 2004 Returned for revision: 11 February 2005 Accepted: 3 March 2005 Published electronically: 15 July 2005
• Background and Aims It has recently found that lowland rice grown hydroponically is exceptionally efficient in absorbing 
, raising the possibility that rice and other wetland plants growing in flooded soil may absorb significant amounts of formed by nitrification of 
in the rhizosphere. This is important because (a) this is otherwise lost through denitrification in the soil bulk; and (b) plant growth and yield are generally improved when plants absorb their nitrogen as a mixture of and compared with growth on either N source on its own. A mathematical model is developed here with which to assess the extent of absorption from the rhizosphere by wetland plants growing in flooded soil, considering the important plant and soil processes operating.
• Methods The model considers rates of O2 transport away from an individual root and simultaneous O2 consumption in microbial and non-microbial processes; transport of towards the root and its consumption in nitrification and uptake at the root surface; and transport of formed from towards the root and its consumption in denitrification and uptake by the root. The sensitivity of the model's predictions to its input parameters is tested over the range of conditions in which wetland plants grow.
• Key Results The model calculations show that substantial quantities of can be produced in the rhizosphere of wetland plants through nitrification and taken up by the roots under field conditions. The rates of uptake can be comparable with those of . The model also shows that rates of denitrification and subsequent loss of N from the soil remain small even where production and uptake are considerable.
• Conclusions Nitrate uptake by wetland plants may be far more important than thought hitherto. This has implications for managing wetland soils and water, as discussed in this paper.
Key words: Ammonium, flooded soil, modelling, nitrate, nitrification–denitrification, rice, rhizosphere, root aeration, soil aeration, wetland plants
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