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Evidence of short-term belowground transfer of nitrogen from Acacia mangium to Eucalyptus grandi trees in a tropical planted forest

Ribeiro Paula R., Bouillet J.P., Trivelin P.C.O., Zeller B., De Moraes Gonçalves J.L., Nouvellon Y., Bouvet J.M., Plassard C., Laclau J.P.. 2015. Soil Biology and Biochemistry, 91 : p. 99-108.

DOI: 10.1016/j.soilbio.2015.08.017

The short-term belowground transfer of nitrogen from nitrogen-fixing trees to companion trees has never been studied in the field. A 15N pulse-labeling study was conducted in a mixed plantation of Acacia mangium and Eucalyptus grandis at the peak of leaf area, 26 months after planting. 15N¿NO3- was injected into the stem of one big Acacia tree in three plots. 15N was traced over 2 months in the labeled Acacia tree as well as in neighboring Eucalyptus trees. For both species, young leaves were sampled, as well as fine roots and the rhizosphere at a distance of 0.75 m and 2.25 m from the labeled tree. The 15N atom% was also determined in the wood, bark, branches and total foliage of the 3 labeled Acacia trees and 9 Eucalyptus trees, 60 days after labeling. Most of the leaves, fine roots and rhizosphere samples of both species were 15N enriched from 5 days after labeling. The d15N values were higher at a distance of 0.75 m than at 2.25 m in Acacia roots, but were similar at both distances in Eucalyptus roots and the rhizospheres. The wood and bark of Eucalyptus trees sampled at a distance of 6.2 m from the labeled Acacia trees were 15N enriched. This shows belowground N transfer from Acacia to Eucalyptus trees in the field during the first few days after labeling. This facilitation process may provide a significant amount of the nitrogen requirements of trees close to N-fixing trees in mixed forests.

Mots-clés : forêt mélangée; plantation forestière; acacia mangium; eucalyptus grandis; arbre fixateur d'azote; injection d'arbres; fixation de l'azote; rhizosphère; mycorhization; espacement; racine; analyse de tissu foliaire; bois; Écorce; brésil

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