Neutral and acidic sugars in particle-size fractions as influenced by climate

Changes in the composition and amount of saccharides have been shown to ref lect soil organic matter (SOM) dynamics, The effect of climate on soil mono saccharide pools was investigated in this study. Particle-size fractions we re obtained from composite samples taken from the top 10 cm of soil at 18 n ative 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-mu m (clay), 2- to 20-m u m (silt), 20- to 250-mu m (fine sand), and 250- to 2000-mu m (coarse sand ) size separates, As particle size decreased, the concentration of monosacc harides decreased significantly from 297 g kg(-1) soil organic C (SOC) in c oarse 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 decreasi ng particle size, indicating that SOM of the finer fractions contained more microbe-derived saccharides, this effect being more pronounced at lower MA T. The concentrations of neutral saccharides decreased in silt and fine-san d fractions as MAT decreased, but increased in all fractions <250 mu m as M AP increased. The concentration of acidic sugars in clay and silt was relat ed only to MAP. The results suggest that the moisture regime primarily affe cted the saccharide concentrations of the finer particle-size fractions, wh ereas the temperature regime affected primarily the saccharide concentratio ns of the coarser fractions. Particle-size fractionation was thus a useful tool in decoding the differing effects of MAT and MAP on saccharide dynamic s.