Response of mycorrhizal seedlings of SW Australian sandplain Epacridaceae to added nitrogen and phosphorus

The responses of seedlings of four species of southwestern Australian sandplain Epacridaceae to added phosphate (P), added NH4NO3 (N) or Complete nutrients were studied in glasshouse pot culture using cores of habitat soil as rooting substrate. Positive responses to N and Complete nutrients were evident for three species in terms of shoot height and shoot dry weight in comparison with Control plants supplied only with deionized water, but no species responded significantly in its shoot growth to P. Root dry weight was generally less in Complete and N treatments compared to P and Control, leading to considerably higher shoot: root ratios in the former two treatments. There was no effect of treatment on infection intensity of hair roots. Root xylem sap composition showed greatly elevated levels of nitrogen in the Complete and N treatments and of phosphate in the P treatment. Ammonium comprised the major nitrogenous solute of xylem in Control and P treatments while nitrate levels exceeded ammonium in Complete and M treatments. Glutamine levels were particularly high in the P treatments. Labelling of the Complete or N treatments with (NH4)-N-15 or, or (NO3)-N-15, (supplied as single labelled ammonium nitrate) indicated that both forms of N were taken up and incorporated into plant insoluble N.