Amino Sugar Signature of Particle-Size Fractions in Soils of the Native Prairie as Affected by Climate

Characterizing the amino sugar signature in particle-size fractions allows elucidation of the fate of microbially derived compounds during the alteration and turnover of soil organic matter (SOM) in soils of different climate regimes. The purpose of this study was to evaluate amino sugar pools and the effect of climate on such pools in particle-size fractions of 18 surface (0-10 cm) soil samples along a climosequence in the native North American prairie. Soils were fractionated into clay (<2 μm), silt (2-20 μm), fine sand (20-250 μm), and coarse sand (250-2000 μm). Soil organic carbon, glucosamine, mannosamine, galactosamine, and muramic acid were then determined in the fractions. The major proportion of the three hexosamines (69%) and muramic acid (79%) was attached to clay. The proportions of clay-associated amino sugars were positively related to mean annual temperature (MAT), and those of silt were negatively related to MAT. This indicated a shift of amino sugars from silt to clay as MAT increased. The total concentration of the four amino sugars in SOM increased markedly from coarse sand (30 g kg−1 SOM) to clay (93 g kg−1 SOM), indicating a progressive accumulation of microbially derived components in SOM with decreasing particle-size. The enrichment factors of the three hexosamines in the SOM of clay were correlated positively with MAT (r = 0.79***), whereas those of muramic acid related positively to mean annual precipitation (MAP) (r = 0.60**). The result suggested that the dynamics of hexosamine were different from those of muramic acid. The amino sugar ratios were controlled by MAT and MAP, but the effect was different in different size fractions. Nevertheless, the two climatic elements are the key site variables that determine the fate of microbially derived compounds in the native grassland soils.