The phosphorus requirement of N2-fixing and urea-fed Acacia mangium

Authors

  • JÉRǑME RIBET,

    1. Laboratoire de Recherche sur les Symbiotes des Racines, INRA, Place Viala, 34060 Montpellier Cedex, France
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  • JEAN-JACQUES DREVON

    Corresponding author
    1. Laboratoire de Recherche sur les Symbiotes des Racines, INRA, Place Viala, 34060 Montpellier Cedex, France
    • *To whom correspondence should be addressed.

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summary

The fast-growing leguminous tree Acacia mangium Willd, was grown for at least 22 wk in aerated solution culture either under N2-fixing conditions or with 2 mmol urea per plant per wk. Inorganic phosphorus was supplied at between 1 and 100 μmol P1 per plant per wk: the latter was determined to be the optimum P supply for growth. The external P requirement for growth and the efficiency of utilization of internal P were similar for both N sources. However, shoot growth and the concentrations of N and P in leaves were decreased by P deficiency to a slightly higher extent in N2-fixing plants than in urea-fed plants. Even though P deficiency limited nodule growth more drastically than it did shoot growth, the fraction of P allocated to both nodules and nodule nitrogenase activity (acetylene reduction) increased with P deficiency. It is concluded that this increase in nitrogenase activity reflects a higher N requirement per unit nodule mass in P-deficient plants and that, once nodules are fully functional the efficiency of utilization of internal P in N2-fixing A. mangium is high compared with that of other N2-fixing legumes.

Abbreviations
ARA

acetylene-reducing activity

C2H2-ID

acetylene-induced decline of nodule nitrogenase ARA

PUE

phosphorus utilization efficiency

WAT

weeks after transplanting

Ancillary