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

Abstract

-European gorse (Ulex europaeus L.) N 2 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 P 2 O 5 .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 15 N natural abundance method. One of the prerequisites of this method is the existence of a significant difference between the 15 N/ 14 N 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 ± 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.Ulex europaeus / symbiotic N 2 fixation / 15 N natural abundance / P fertilization / Pinus pinaster 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 P 2 O 5 .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 15 N. Cette méthode nécessite notamment une différence significative entre les rapports 15 N/ 14 N 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 ± 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.Ulex europaeus / fixation symbiotique de l'azote / abondance naturelle en 15 N / fertilisation en phosphore / Pinus pinaster

Weak Evidence of Regeneration Habitat but Strong Evidence of Regeneration Niche for a Leguminous Shrub

“…Such a pattern in 2011 might be the consequence of a small sample size during a period of variable and increasing fixation rate from the seedling stage to the adult stage. Indeed, in an additional sample made in 2013, there was no difference of fixation rate between fertilised plants and control plants (unpublished data) and this later result is consistent with the low limitation of nitrogen fixation rate by phosphorus availability found for the mature legumes of this forest [ 40 ] as well as in most regions of the world [ 9 ]. Overall P fertilisation did not have much influence on the functioning of the symbiosis (see also S2 File ).…”

Effects of fire and three fire-fighting chemicals on main soil properties, plant nutrient content and vegetation growth and cover after 10 years

“…For the leguminous species (P. tridentatum and U. micranthus) there was a positive correlation between plant total N and P (r = 0.621 to 0.691; p b 0.005). Although contradictory results have been reported about the effects of P fertilization on N 2 fixation rates in legumes (see Cavard et al (2007) and references therein), the N-P correlation we found could be due to an enhanced N 2 fixation due to P fertilization because biological N 2 -fixation is a P-demanding process (Rodríguez-Echeverría et al, 2009).…”

Global assessment of limitation to symbiotic nitrogen fixation by phosphorus availability in terrestrial ecosystems using a meta‐analysis approach

“…The discrepancy between the results presented here (i.e., experiments based on nutritive solutions versus experiments using soils) is in line with the occasional controversy reflected in the scientific literature [e.g., Israel , ; Robson et al ., ]. The discrepancy would be explained if soil available P was most of the time high enough to enable a high fixation rate [ Cavard et al ., ]. We could not test this hypothesis because soil P availability data were very scarce, and the few studies in which soil P availability was measured used different soil P extraction methods.…”