Land use effects on amino sugar signature of chromic Luvisol in the semi-arid part of northern Tanzania

Characterizing amino sugar signature in particle size separates of tropical soils is important for further understanding the fate of microbial-derived compounds during the decomposition of soil organic matter (SOM) in tropica l agroecosystems. We investigated the impact of land-use changes on the nat ure, amount and dynamics of amino sugars in soil of the semi-arid northern Tanzania. Samples were collected from the uppermost 10 cm of native woodlan d, degraded woodland, fields cultivated for 3 and 15 years and homestead fi elds fertilized with animal manure. The amount of glucosamine, galactosamin e, mannosamine and muramic acid were determined in bulk soil and size separ ates. Compared to the native woodland, a 68% and 72% reduction in total ami no sugar contents were found in the 3- and 15-year cultivated fields, respe ctively. Moreover, 39% of the total amino sugar was lost from the degraded woodland. This may be attributed to accelerated decomposition of amino suga rs and/or decreasing microbial biomass input under the semi-arid environmen t following clear-cutting and cultivation. In contrast, only a 20% decline was found from the fields where animal manure had been applied. Most of the amino sugar depletion occurred from the coarse and fine sand-associated SO M. The decline from the silt and clay-bound amino sugar was relatively smal l, indicating the importance of organo-mineral associations in the stabiliz ation of microbial-derived sugars in this tropical soil. After 15 years of continuous cultivation, the ratio of glucosamine:galactosamine increased fr om 1.44 to 2.23, while the ratio of glucosamine:muramic acid increased from 14.5 to 26.5 (P<0.05). These results suggest that cultivation may have led to preferential depletion of bacterial-derived amino sugars (muramic acid and galactosamine) compared with fungal-derived glucosamine.