Amino sugars in arctic soils

Abstract

Amino sugars in soils are assumed to be of microbial origin. Their levels in soil, can provide insights into the microbial contribution to soil organic matter (SOM) and might serve as an indicator of SOM quality. Four amino sugars, glucosamine, galactosamine, mannosamine, and muramic acid were determined by gas chromatography in five soils from the tundra Alaska before and after incubation for 4 months at 4 and 25°C. Glucosamine and muramic acid analyses were utilized to represent fungal biomass and bacterial biomass, respectively. Total amino sugar N represented 0.8 to 3.3% of the total soil N in these five tundra soils, and the proportion of soil N as amino sugars increased with depth. Total amino sugar and fungal glucosamine N increased or remained constant during incubation at 4 and 25°C (except site 3 Cf horizon which decreased after incubation at 4°C), suggesting that total microbial biomass and fungal biomass increased. Bacterial biomass had an increase after incubation at 4°C, and a relative decrease at 25°C (except for Cf horizon). Fungal glucosamine to muramic acid ratios demonstrated that fungal biomass increased faster than bacterial biomass at 25°C, and slower at 4°C, indicating that at higher temperature, fungi dominated the microbial biomass in the soils studied. The mechanisms involved in the accumulation and decomposition of amino sugars in soil during incubation were not clear. No correlations were observed between the amino sugar contents and CO₂ evolution during incubation, indicating that amino sugar abundance may not be an indicator of the bioavailability of SOM in soils. However, they can provide insights into the microbial contribution to SOM.

Acknowledgments

The authors gratefully acknowledge the field assistance of J. M. Kimble and the comments and suggestions on the manuscript by J. M. Kimble. Financial support was provided by the ARCSS-LAII program of the National Science Foundation, Office of Polar Programs.