RESUMEN
We carried out an experiment including nitrogen addition (N, 50 kg N·hm-2·a-1), phosphorus addition (P, 25 kg P·hm-2·a-1) and both nitrogen and phosphorus addition (NP, 50 kg N·hm-2·a-1+25 kg P·hm-2·a-1) in a natural Korean pine broad-leaved mixed forest on Changbai Mountain to examine the effects of single and combined N and P additions on soil microbial community composition and amino sugar. The results showed that N and P addition significantly reduced total microbial biomass by 19.5% and 24.6% in the organic layer of soil, while P addition significantly reduced the biomass of bacteria and fungi by 23.8% and 19.3%, respectively. In the mineral layer, N, P and NP addition significantly increased total microbial biomass by 94.8%, 230.9%, and 115.0% respectively, while the biomass of bacteria and fungi were significantly increased under all the treatments. The fungi to bacteria ratio (F/B) was significantly increased in the organic layer by N addition, while was decreased in the mineral layer soil by NP addition. The Gram-positive bacteria to Gram-negative bacteria ratio showed positive response to N, P and NP addition. Soil amino sugars responded differently to different treatments. N, P and NP addition significantly decreased glucosamine content by 41.3%, 48.8% and 36.4% in the organic layer, while N and NP addition increased muramic acid content by 43.0% and 71.1%, respectively. The contents of glucosamine and muramic acid in the mineral layer did not change significantly in response to N addition but increased significantly in response to both P addition and NP addition. The glucosamine to muramic acid ratio in the organic layer significantly decreased under fertilization treatments, indicating that N and P addition increased the relative contribution of bacteria to soil organic carbon accumulation. The changes in soil amino sugar contents were closely related to the change in microbial community composition after N and P addition, both of which were affected by changes in soil chemical properties.