Effects of substrates on dynamics of amino sugars in two different stages of succession in forest soil

Dynamics of three kinds of amino sugars (glucosamine, galactosamine and muramic acid) in Masson pine and monsoon forest soil in two different stages of succession in Dinghu Mountain, southern China, was amended with glucose and different amounts of inorganic nitrogen in experiment of incubation at a constant temperature of 25 ℃. Relative contribution of microbial communities to carbon and nitrogen immobilization was explored in relation to the ratio of glucosamine to muramic acid. Results showed that during the whole incubation, the total amount of soil amino sugar in the monsoon forest was significantly higher than in the Masson pine forest. At the early period of incubation, the total amount of soil amino sugars increased at a significantly higher rate in the monsoon forest than in the Masson pine forest. With prolonged incubation, the total amount of soil amino sugars decreased to a larger extent in the Masson pine forest than in the monsoon forest. The response of heterogeneous amino sugars was compound-specific. Muramic acid exclusively originated from bacteria was more easily to be affected by glucose and inorganic N supplies, while fungal cell wall residues such as glucosamine were more stable than those derived from bacteria. The ratio between glucosamine and muramic acid reflects the relative contributions of fungal and bacterial residues in organic matter accumulation and transformation process. The bacteria are more easily available in the early culture of exogenous substance, but as the culture progresses, fungi occupy a dominant position. However, the ratio of carbon to nitrogen in the substrate had no significant effect on the total amount of amino sugars. Compared to the Masson pine forest, utilization of available substrates could significantly stimulate the microbial fixation of carbon and nitrogen in the monsoon forest soil, and thus more microbial residues were produced and accumulated in soil. As a whole, the dynamics of amino sugars is closely associated with the coupling effect of soil carbon and nitrogen, thus playing an important role in regulating supply and requirement of carbon and nitrogen in soil.