Role of Acacia Spp. In Nutrient Balance and Cycling in Regenerating Eucalyptus regnans F. Muell. Forests. II. Field Studies of Acetylene Reduction

Abstract

Rates of C₂H₂ reduction by nodules of Acacia dealbata growing in 2-year-old Eucalyptus regnans regeneration were determined at monthly intervals for 1 year under field conditions. Intact soil cores containing roots and nodules showed maximum values of 7.1 μmol h^-1 g^-1 fresh weight of nodules with a mean value of 4.4 μmol h^-1 g^-1 fresh weight. Nodule mass was clearly related to climatic conditions, being greatest when both temperature and moisture levels were favourable, and was probably depressed during the sampling period by the prevailing severe drought. From the measured rates of C₂H₂ reduction, estimated N₂ fixation was 12-32 kg ha^-1 year^-1. Rates of N₂ fixation as high as this confirm the role of acacias as fast-growing pioneer species important in maintaining the nitrogen pool of the forest ecosystem.