Field effect of P fertilization on N2 fixation rate of Ulex europaeus

Free access article

Issue		Ann. For. Sci. Volume 64, Number 8, December 2007


Page(s)		875 - 881
DOI		10.1051/forest:2007066
Published online		22 November 2007

Ann. For. Sci. 64 (2007) 875-881
DOI: 10.1051/forest:2007066

Field effect of P fertilization on N₂ fixation rate of Ulex europaeus

Xavier Cavard^a, Laurent Augusto^a, Etienne Saur^b and Pierre Trichet^c

^a UMR 1220 TCEM (INRA), BP 81, 33883 Villenave d'Ornon Cedex, France
^b UMR 1220 TCEM (ENITAB), 1 cour du Général de Gaulle, BP 201, 33175 Gradignan Cedex, France
^c UR 1263 EPHYSE (INRA), 69 route d'Arcachon, 33612 Cestas Cedex, France

(Received 14 December 2006; accepted 26 April 2007; published online 22 November 2007)

Abstract - European gorse (Ulex europaeus L.) N₂ fixation rate (%Ndfa) was studied in a maritime pine (Pinus pinaster Aït.) oligotrophic forest. Fertilization field trials were carried out on 5 sites with various inputs of phosphorus (0-240 kg P₂O₅.ha^-1). Seven to ten years after pine planting, gorse were sampled to evaluate the effect of P fertilization on gorse %Ndfa, determined using the ¹⁵N natural abundance method. One of the prerequisites of this method is the existence of a significant difference between the ¹⁵N/¹⁴N ratios in the atmospheric N reference and in the stand soil N references. This prerequisite was satisfied for 80 of 120 cases. The average %Ndfa was high (70 $\pm$ 3%) but with high local variability. No significant difference in %Ndfa was detected among P treatments. Nitrogen concentration of gorse was significantly higher in the highest dose treatments compared to the control.

Résumé - Effet in situ de la fertilisation en phosphore sur le taux de fixation de l'azote atmosphérique d'Ulex europaeus. Le taux de fixation de l'azote atmosphérique (%Ndfa) de l'ajonc d'Europe (Ulex europaeus L.) a été étudié dans une forêt oligotrophe de pins maritimes. Des essais de fertilisation ont été établis avec plusieurs niveaux d'apport en phosphore (0-240 kg P₂O₅.ha^-1). Sept à dix ans après la plantation de pins, les ajoncs ont été échantillonnés afin d'évaluer l'effet de la fertilisation en phosphore sur le %Ndfa, calculé par la méthode de l'abondance naturelle en ¹⁵N. Cette méthode nécessite notamment une différence significative entre les rapports ¹⁵N/¹⁴N de la référence atmosphérique et de la référence du sol des peuplements. Cette condition était satisfaite dans 80 cas sur 120. Le %Ndfa moyen était élevé (70 $\pm$ 3 %) mais avec une grande variabilité locale. Aucune différence des %Ndfa n'a été détectée entre les traitements. Les teneurs en azote des ajoncs étaient significativement plus élevées pour les doses maximales que pour les témoins.

Key words: Ulex europaeus / symbiotic N₂ fixation / ¹⁵N natural abundance / P fertilization / Pinus pinaster

Mots clés : Ulex europaeus / fixation symbiotique de l'azote / abondance naturelle en ¹⁵N / fertilisation en phosphore / Pinus pinaster

Corresponding author: laugusto@bordeaux.inra.fr

© INRA, EDP Sciences 2007

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