Title: THE ASSESSMENT OF NITROGEN FIXATION AND THROUGHPUT BY LICHENS
Abstract: S ummary Using specially made controlled environment chambers, the rates of nitrogen fixed in the field by the lichens Peltigera membranacea, P. polydactyla and Lobaria pulmonaria have been estimated under simulated seasonal conditions. The chambers permitted direct comparisons between short term acetylene reduction estimates and long term incorporation of 15 N 2 labelled gas. Large thallus samples minimized variation, and the overall figures of N 2 fixed integrated the effects of fluctuations in temperature, daylength, light intensity and thallus moisture content. Empirical factors have been derived to relate short term rates of acetylene reduction to long term rates of N 2 incorporation. Under predominantly moist conditions, factors of 8 to 10 were found. Drier summer conditions can result in factors in excess of 20. Estimated rates of total nitrogen input were 4 to 6 kg ha −1 per year. In dry exposed situations rates can be approximately half this figure.