Nitrogen fixation associated with bryophytes colonizing burnt sites in Southern Tasmania, Australia

Abstract

Soil cores containing bryophytes collected monthly over a period of 14 months from sites burned in three successive years were assayed for acetylene reduction activity. This activity was converted, using an experimentally determined C₂H₂: N₂ ratio of 3.54, to nitrogen fixation rates of 43,99 and 152 mg N m⁻² in the second, third and fourth years, respectively, after burning. Marchantia berteroana, Ceratodon purpureus and Funaria hygrometrica showed high activity with rates of acetylene reduction up to 553 nmol C₂H₄ g⁻¹ h⁻¹. There was no significant relationship between acetylene reduction rates and assay temperature, moisture of the cores during assay, or with the organic matter (loss on ignition), nitrogen or phosphorus content of the soil. Rates of acetylene reduction for samples from experimental sites were similar to those from adjacent undisturbed forest at a single time of assay. However, when the activities were measured for samples of individual species of bryophytes, samples from the forest were considerably less active than those collected from burned areas.