Abstract: Soil microorganisms play an important role in carbon and nitrogen cycling. Changes in litterfall and soil properties due to stand age can have important implications to soil carbon (C) and nutrient cycling via microbial pathway. Soil degradation has widely occurred in Larix principisrupprechtii plantation because of its simple forest structure; however, little is known about how soil nutrients are related to soil microbial properties. Here we determined soil microbial responses to different aged L. principisrupprechtii plantations (18-, 35-, and 51-year-old) in Taiyue Mountain of Shanxi Province. The results showed that soil microbial biomass C and the proportion of microbial biomass C to the sum of microbial biomass C and dissolved organic C increased with the increase of stand age. Soil microbial biomass C/N ratio in the 51-year-old L. principisrupprechtii plantation was the highest (13), being 60% higher than that in the 18- and 35-year-old L. principisrupprechtii plantations. The microbial carbon entropy ranged from 1.5% in the 35-year-old L. principisrupprechtii plantation to 2.8% in the 18-year-old L. principisrupprechtii plantation. Soil microbial biomass N, fungal Shannon diversity, soil and litter C/N ratios decreased in the following order: 35yearold > 18yearold > 51-year-old plantations. Fungal community structure diversity had a direct effect on soil microbial biomass C, while litter C/N had a significant effect on soil microbial biomass N, and soil and microbial biomass C/N ratios were the direct factors regulating soil fungal community structure diversity. In general, the active organic C content in the 35-year-old L. principisrupprechtii plantation was lower than those in the other two plantations, and its carbon pool was more stable and nutrient situation was better.

Key words: altitude, genetic diversity, Sassafras tsumu, genetic structure.