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Distribution of Nitrogen Fixed in Desert Algal-Crusts¹

ABSTRACT

Fixation of isotopically labeled N₂ by desert algal crust organisms was very rapid after initial wetting of crusts. After 8 days of incubation, a steady rate of fixation was reached which continued for 152 days.

The initial distribution of N was 4% extracellular NH₄, 16% acid-hydrolyzable NH₄ (included extracellular NH₄), 41% amino acid, 4% hexosamine, 29% acid-hydrolyzable but unidentified, and 11% non-hydrolyzable. After 21 days of incubation the distribution of total N was 2, 18, 42, 2, 29 and 11%, respectively. The distribution of excess N¹⁵ after 21 days of incubation was trace, 12, 51, 2, 29 and 7% for the respective fractions. Continued incubation had little effect on the relative distribution of N in the several fractions.

¹ Journal Paper No. 1075 of the Arizona Agr. Exp. Sta., Tucson. This research was supported in part by the Cooperative Western Regional Research Project W-85. Presented before Div. S-3, Soil Science Society of America, Nov. 1965, Columbus, Ohio.

² Formerly Graduate Assistant (now Research Soil Scientist, Soil and Water Conservation Div., ARS, USDA, Kimberly, Idaho), and Assistant Professor, Department of Agricultural Chemistry and Soils, Univ. of Arizona, Tucson, respectively.

Received for publication January 24, 1966. Accepted for publication April 27, 1966.