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Nitrogen Fixation by Blue-Green Algae-Lichen Crusts in the Great Basin Desert¹

R. C. Rychert and J. Skuji

ABSTRACT

Blue-green algae-lichen crusts (Atriplex confertifolia, Eurotia lanata, and Artemisia tridentata sites) from the Great Basin Desert have a laboratory potential of fixing atmospheric nitrogen at rates up to 84 g of N ha^-1 hour^-1. Nitrogen fixation is optimal when the crust is moistened to - bar pressure, temperature is 19 to 23C, and the light intensity is 200 microeinsteins m^-2 sec^-1 with incandescent light. The acetylene reduction technique provided a useful assay to measure in situ nitrogen fixation which was correlated with potential values obtained in the laboratory under optimum conditions. Nitrogen fixation was found to be reduced under desert shrub canopies possibly due to allelopathic effects of the shrubs. Aqueous leaf extracts of desert shrubs significantly inhibited nitrogen fixation. Annual nitrogen fixed was estimated at 10 to 100 kg of N ha^-1 year^-1, depending upon microenvironmental conditions.

¹ Contribution from the Ecology Center, Utah State Univ., Logan 84322. This work was supported through the US IBP Desert Biome program by National Science Foundation Grant no. GB-15886.

Received for publication March 4, 1974. Accepted for publication June 6, 1974.