PURINES AND PYRIMIDINES IN SOILS AND HUMIC SUBSTANCES

Purines and pyrimidines were determined by ion-exclusion chromatography in soils and humic substances of widely differing origins. Concentrations of purines + pyrimidines ranged from 20.9-137.7 .mu.g/g of dry soils, from 210.8-810.0 .mu.g/g of dry, ash-free humic acids, and from 294.3-1086.6 .mu.g/g of dry, ash-free fulvic acids. Quantitatively the distribution in soils was as follows: guanine > cytosine > adenine > thymine > uracil. Humic acids were richer in guanine and adenine but poorer in cytosine, thymine and uracil than were pulvic acids. Guanine + cytosine over adenine + thymine ratios for soils and humic substances averaged > 2 and methyl cytosine was not detected, suggesting a microbial DNA origin for the nucleic acid bases extracted. The proportion of total N in purines + pyrimidines was inversely proportional to the total N content. An average 3.3% of the total N in the inorganic soils but only 0.3% of the total N in the organic soils analyzed occurred in nucleic acid bases.