Nitrogen fixation (acetylene reduction) by Acacia pellita on areas restored after mining at Groote Eylandt, Northern Territory
Australian Journal of Botany
27(4) 353 - 361
Factors affecting the reduction of acetylene to ethylene by nodules of Acacia pellita O. Schwarz were studied on 3-year-old trees in the field. The specific activity of rooted nodules (22.8 ± 3.3 nmol mg-1 fresh wt h-1) was greater than that of detached nodules alone (13.5 ± 2.1 nmol mg-1 h-1). Acetylene reduction started without a lag phase and remained linear for about 4 h. The apparent Km value for acetylene was derived to be 11.2 x 10-3 atm. Nodule material could be kept successfully without loss of activity when moist and shaded from direct sunlight for periods of up to 1 h. Acetylene reduction ceased when the assay temperature was 0°C, activity increasing to 20.3 ± 2.3 nmol mg-1 h-1 at 22°. The Acacia plants exhibited a diurnal cycle of nitrogen (acetylene) fixation; the greatest specific activity at midday was 27.7 ± 4.8 nmol mg-1 h-1 when the shaded soil temperature was 32°C and photosynthetically active radiation was 2550 μE m-2 s-1. By using a regression of nodule number per tree on stem diameter to obtain the total number of nodules per hectare, the total nitrogen fixation per wet season was estimated to be 12 ± 4 kg ha-1 where the planting density in the study area was 1110 trees ha-1.
The work is discussed with reference to its implications for management of the restored areas and the role of acacias as nitrogen-fixing plants in the pre-mining native Eucalyptus tetrodonta open-forest.
© CSIRO 1979