Nitrogen Fixation by Native Australian Legumes

Abstract

Nitrogen fixation was studied by the acetylene-reduction technique in root nodules of 10 native Australian legumes in three habitats in Victoria: low open-forest. sandy heathland and coastal sand dunes. Nodular activity reached a maximum in spring (and in autumn in sand-dune species), declined to a minimum in late summer and continued at a low level throughout winter. Mean nitrogenase activity was 1.73 μmol C₂H₂ reduced g^-1 fresh wt nodules h^-1, with spring maxima 8-250 times summer minima. It is suggested that variations in rainfall and temperature were the major factors influencing seasonal variations in nodular activity. Estiniates of minimum acetylene reduction per hectare per year were derived from measurements of seasonal and diurnal variations in acetylene reduction and abundance of nodules per hectare, and were used to derive approximate minimum values for nitrogen fixation of 0.004-0.746 kg ha^-1 yr^-1. The quantities of nitrogen fixed are compared with other reports and the significance of nitrogen fixation by these native legumes is discussed.