Interactions between mycorrhizal colonisation, nodulation and growth of Calliandra calothyrsus seedlings supplied with different concentrations of phosphorous solution

Interactions between arbuscular mycorrhizal colonisation, nodulation and growth of Calliandra calothyrsus were investigated in an experiment in which mycorrhizal and non-mycorrhizal seedlings were grown in a glasshouse environment, in pots containing a sterilised substrate and supplied with four different concentrations of phosphorus solution (0, 7.5, 15 and 30 mg l(-1) P). All seedlings were inoculated with Rhizobium. After eight weeks growth, assessments were made of stem, leaf and root growth, nodule dry mass and percentage mycorrhizal colonisation. Mycorrhizal colonisation was highest at 0 mg l(-1) P and was reduced with increasing phosphorus application. Mycorrhizal inoculation increased seedling growth and nodulation most at lower concentrations (0 and 7.5 mg l(-1) P) of phosphorus application. Phosphorus application improved growth and nodulation at 7.5 mg l(-1) P compared with 0 mg l(-1) P, but further increase in phosphorus application did not result in further growth benefits. Seedling growth was positively correlated with mycorrhizal colonisation and nodule dry mass with strongest relationships occurring far nodule dry mass. Growth response of seedlings to greater nodulation was maintained in mycorrhizal plants but not in nonmycorrhizal plants, even at high levels of P application when available P was not limiting. It is concluded that C, calothyrsus is dependent on mycorrhizal association in P-deficient soils, and that mycorrhizal inoculation has the potential to enhance its growth and nodulation under these conditions.