Distribution of Nitrogen Fixed in Desert Algal‐Crusts

Abstract

Abstract Fixation of isotopically labeled N 2 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 NH 4 , 16% acid‐hydrolyzable NH 4 (included extracellular NH 4 ), 41% α 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 N 15 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.