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

The responses of seedlings of four species of southwestern Australiansandplain Epacridaceae to added phosphate (P), added NH₄N0₃(N) or Complete nutrients were studied in glasshouse pot cultureusing cores of habitat soil as rooting substrate. Positive responsesto N and Complete nutrients were evident for three species interms of shoot height and shoot dry weight in comparison withControl plants supplied only with deionized water, but no speciesresponded significantly in its shoot growth to P. Root dry weightwas generally less in Complete and N treatments compared toP and Control, leading to considerably higher shoot: root ratiosin the former two treatments. There was no effect of treatmenton infection intensity of hair roots. Root xylem sap compositionshowed greatly elevated levels of nitrogen in the Complete andN treatments and of phosphate in the P treatment. Ammonium comprisedthe major nitrogenous solute of xylem in Control and P treatmentswhile nitrate levels exceeded ammonium in Complete and N treatments.Glutamine levels were particularly high in the P treatments.Labelling of the Complete or N treatments with ¹⁵NH₃ or ¹⁵NO₃(supplied as single labelled ammonium nitrate) indicated thatboth forms of N were taken up and incorporated into plant insolubleN. Key words: Epacridaceae, nitrogen, phosphorus, mycorrhiza, south-west Western Australia