Etienne Saur

Forest floor contribution to phosphorus nutrition: experimental data

Abstract• Although accumulation of decomposing litter temporarily removes nutrients from active circulation, it creates a medium that is more suitable for nutrient uptake where soil conditions are unfavorable.• A pot experiment was conducted using labeling of isotopically exchangeable phosphate ions of the soil and applying the dilution principle to accurately assess the contribution of the forest floor to P nutrition of maritime pine seedlings (Pinus pinaster Aït.). Three-week-old maritime pine seedlings were planted in pots containing either mineral soil (MS) or mineral soil covered with a forest floor layer (MS+FF).• After 130 d, P uptake was still insignificant in the MS treatment while the P content of the seedlings in the MS+FF treatment increased tenfold with respect to the initial P content. In the latter treatment, the forest floor contributed 99.1% of the P supply to pine seedlings.• The higher P uptake from the forest floor than from the mineral soil may be explained by its lower ability to retain inorganic P, which enabled a higher concentration of inorganic P to be maintained in solution.Résumé• Bien que l’accumulation de litière en décomposition immobilise temporairement une partie des nutriments, elle crée un espace propice au prélèvement des nutriments là où le sol minéral est peu favorable.• La contribution des couches holorganiques à la nutrition en P de semis de pin maritime (Pinus pinaster Aït.) a été estimée sur base d’une expérience en pots combinée à un marquage des ions phosphate du sol minéral. Des semis de trois semaines ont été plantés dans des pots contenant soit uniquement du sol minéral (MS) ou soit du sol minéral recouvert par une couche de litière (MS+FF).• Après 130 jours, le prélèvement en P était toujours insignifiant dans le traitement MS alors que le contenu en P des semis du traitement MS+FF avait été décuplé par rapport au contenu initial. Dans ce traitement, la contribution des couches holorganiques à l’alimentation en phosphore des semis était de 99,1 %.• Le prélèvement en P plus important à partir des couches holorganiques peut être expliqué par leur faible capacité de rétention du P qui permet de maintenir une forte concentration en P dans la solution du sol.

Growth and uptake of mineral elements in response to sodium chloride of three provenances of maritime pine 1

Abstract Effect of sodium chloride (NaCl) on the growth, mineral concentration, and net accumulation of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) was established in one‐year‐old seedlings (Iberique, Landais, Tamjoute provenances) grown in a regulated greenhouse in nutrient solutions. Increasing concentration of NaCl induces a reduced rate of growth and the Iberique provenance was most affected. Accumulation of Na is significantly more intense in the Tamjoute provenance irrespective of the growth response. Macronutrient concentration are markedly modified, as a result of salinity, by increases in the N and K concentrations and decreases in P, Ca and Mg concentrations in the root. The nutrient concentrations in the tissues did not appear to become deficient or toxic under these saline conditions. Total accumulation of most ions was reduced as a consequence of relative growth and provide a good indication of geographic provenance response. The results presente...

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

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 ± 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.RésuméLe 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 ± 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.

Micronutrient composition of xylem sap and needles as a result of P-fertilization in maritime pine

Xylem sap and foliar compositions (P, Cu, Zn, Mn) were examined over 4 months in control and P-fertilized maritime pine in a 7-year-old plantation. The absorption of copper, zinc, and boron appears to be reduced by phosphate fertilization. Manganese concentrations are positively related to P-supply increase. Foliar analysis and sap provides the same type of information in terms of antagonism or synergism between elements but the response to treatment is more often significant with sap throughout the seasons and is completely non-existent on a single classical autumn diagnosis with foliar concentration (i.e. Zn and Cu). In consequence foliar analysis is not sensitive enough for copper or zinc deficiency diagnoses in young plantations where nutritional growth disorders appear in a short period of spring, and xylem chemistry appears to be a convenient tool in monitoring micronutrient disorders in pine plantations.

Interactive effects of P-Cu fertilizers on growth and mineral nutrition of maritime pine

The interaction between copper and phosphorus was studied in a pot experiment involving a factorial combination of three levels of copper and three levels of phosphorus applied to maritime pine seedlings growing in podzolic sand.Biomass measurement showed that a single copper fertilization could be toxic to the plant and that better growth was obtained with a combination of both phosphorus and copper fertilization. Copper toxicity was shown to be dependent on phosphorus levels in the plant, and better growth was obtained with an appropriate balance between phosphorus and copper concentrations. A reciprocal inhibition between phosphorus and copper uptake was assumed to explain this pattern.