Saturday, 15 July 2006

Rapid Biosynthesis Process of Amino Sugars in Soil by Using NH4+ and Glucose.

Hongbo He and Xudong Zhang. Institute of Applied Ecology, Chinese Academy of Sciences, No. 72, Wenhua Road , Shenhe district, Shenyang, China

Soil amino sugars, as microbial residues, have been used as biomarker to indicate microorganism contribution to soil organic matter turnover and sequestration. However, it is not clear that how amino sugars are originated in soil, hence it is significant to differentiate between the new-synthesized amino sugars and the old one in order to trace the synthesis process. Laboratory incubation with 15N-labeled NH4+ was conducted and GC-MS technique was used for this aim. Surface soil samples (0-20cm) of Udoll were used and isotope amendments were carried out. The substrate addition was as: (1) (15NH4)2SO4 plus glucose was added once a week, and (2) glucose was added once a week but (15NH4)2SO4 every two weeks. The incubated soils were sampled every two weeks for GC-MS determination and the incorporation of 15N into three amino sugars (glucosamine, galactosamine and muramic acid) was evaluated by abundance ratio of F+1 to the parent fragment F of the amino sugar derivatives and calculated as Atom Percentage Excess (APE). The APE was different among the three amino sugars. When both substrates were added once a week, the APE of muramic acid increased very rapidly at the early stage, but tended to reach an equilibrium level just after 8 weeks, while the APE of glucosamine increased almost linearly until the 15th week and then tended to become slow. The enrichment ratios of 15N in glucosamine were smaller than that of muramic acid, but they were close at the later stage of 18-week incubation. Because soil amino sugars are heterogeneous, the characteristics of APE can not only reflect the biosynthesis speed and timing characteristics of soil amino sugars but also deduce the activity of different microorganism communities, i. e. bacteria could react with N nutrient and C substrate addition faster, while fungi could utilize the N nutrient released by bacteria at the later stage. For the amendment with N nutrient added every two weeks, the APE characteristics of amino sugars were changed significantly with different pattern except galactosamine. The lack of N at the early stage limited microbial growth significantly, which was contributed to the APE decrease of muramic acid and glucosamine. While the carbon source was relatively abundant during the subsequent incubation to ensure the efficient utilization of NH4+, so the similar APE of muramic acid at the later stage was presented. In summary, amino sugars are rapidly synthesized in soil and the synthesis process is highly related to the availability of N nutrient and C sources. This finding may be significant for the understanding of microbial immobilization of N in soil. Key words: amino sugar, biosynthesis, 15N, glucose, soil.

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