Monosaccharide Distribution of Soils on a Toposequence in the Humid Tropical Rainforest, Southeastern, Nigeria

Abstract

Soil monosaccharide distribution provides useful information about its carbohydrate origin and tendency for carbon sequestration. Monosaccharide (glucose, galactose, mannose, arabinose and xylose) distribution of soils on a toposequence in Mbano, southeastern, Nigeria was estimated by extracting 1g soil with 25 mls of 80% hot alcohol. Experimental design was a 2 x 3 x 5 factorial of horizon, physiography and monosaccharides in a randomized complete block setup with 3 replications. Also monosaccharide contents were correlated and regressed with soil properties. Mean monosaccharide contents averaged over horizons and physiography varied as 0.03, 0.07, 0.68, 0.74 and 0.88% in increasing order of glucose < galactose < mannose < xylose < arabinose. Also, averaged over horizon and monosaccharides, mean values were 0.62, 0.79 and 0.98% in increasing sequence of toe-slope < summit < mid-slope physiographic positions. Averaged over physiographic positions and monosaccharide contents, concentrations  of AB (0.670%) was distinctly (LSD 0.05) better than A (0.30%) horizons. Galactose+mannose/arabinose+xylose and mannose/xylose ratios were less than unity indicating that the carbohydrates were of plant origin. Also, mean arabinose/xylose and xylose/mannose ratios were greater than unity, signifying fresh plant tissues with high decomposition rates respectively. Soil monosaccharides correlated (P < 0.05) with the bulk density, clay, ECEC, moisture content, pH, total porosity, P and organic carbon with less than 20% of the monosaccharides accounted by the soil properties. In general, the soil carbohydrates originated from fresh rapidly decomposing plant tissues with poor tendency for carbon sequestration.

Keywords: Monosaccharide, toposequence, carbon sequestration, humid tropics and southeastern Nigeria