Use of a 15N2 labelling technique to estimate exudation by white clover and transfer to companion ryegrass of symbiotically fixed N
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Backgrounds and aims
N rhizodeposition by legumes leads to enrichment of N in soils and in companion plants. N rhizodeposition can be divided into two major components, root exudation and root senescence. Our aim was to quantify N root exudation in white clover (Trifolium repens L.) through an estimation of short-term N rhizodeposition and to assess its impact on N transfer to companion perennial ryegrass (Lolium perenne L.) grown in mixture with clover.
15N2 provided in the root atmosphere for 3 days was used to estimate transfer of symbiotically fixed nitrogen (SFN) to the growing medium by clover grown in pure stand and to ryegrass by clover grown in mixture for 2 months.
The proportion of N rhizodeposited over the 3 days increased from 3.5 % of SFN in pure stand to 5.3 % in mixture. The 15N-enrichment of ammonium from the adhering substrate shows that a part of the rhizodeposited N was released in the form of ammonium. 4 % of the rhizodeposited N was taken up by ryegrass during the labelling period.
This study showed a significant contribution of root N exudation to the total N rhizodeposition of legumes and in the transfer of N to grasses.
KeywordsRhizodeposition Nitrogen Clover Ryegrass Transfer Ammonium
We thank Anne-Françoise Ameline for technical assistance during the labeling experiment and Marie-Paule Bataille for ammonium and isotopic analysis. We are grateful to Dr Laurence Cantrill for English improvement of the manuscript.
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