Neutral and Acidic Sugars in Particle‐Size Fractions as Influenced by Climate

Abstract

Changes in the composition and amount of saccharides have been shown to reflect soil organic matter (SOM) dynamics. The effect of climate on soil monosaccharide pools was investigated in this study. Particle‐size fractions were obtained from composite samples taken from the top 10 cm of soil at 18 native grassland sites along mean annual temperature (MAT) and precipitation (MAP) transects from Saskatoon, Canada to southern Texas, USA. Neutral and acidic sugars were determined in the bulk soil, <2‐μm (clay), 2‐ to 20‐μm (silt), 20‐ to 250‐μm (fine sand), and 250‐ to 2000‐μm (coarse sand) size separates. As particle size decreased, the concentration of monosaccharides decreased significantly from 297 g kg−1 soil organic C (SOC) in coarse sand to 174 g kg−1 SOC in the silt fractions, but increased to 239 g kg−1 SOC in clay. Ratios of hexoses to pentoses increased with decreasing particle size, indicating that SOM of the finer fractions contained more microbe‐derived saccharides, this effect being more pronounced at lower MAT. The concentrations of neutral saccharides decreased in silt and fine‐sand fractions as MAT decreased, but increased in all fractions <250 μm as MAP increased. The concentration of acidic sugars in clay and silt was related only to MAP. The results suggest that the moisture regime primarily affected the saccharide concentrations of the finer particle‐size fractions, whereas the temperature regime affected primarily the saccharide concentrations of the coarser fractions. Particle‐size fractionation was thus a useful tool in decoding the differing effects of MAT and MAP on saccharide dynamics.