Abstract: [Objective] The rhizosphere plays an vital role for microbial-driven carbon and nitrogen sequestration and nutrient cycling of terrestrial ecosystems. Studies on dynamic of microbial biomass in rhizosphere soil can help us understand the mechanism of utilization and cycle of carbon and nitrogen, and also provide a scientific basis for forest protection and rational management in the study area.[Method] Taking the coniferous and broad-leaved mixed forest as the research object, the rhizosphere and non-rhizosphere soil samples were collected using shaking off method in the forests dominated by the main native tree species in the cold temperate forests of China (Pinus sylvestris var. mongolica, Larix gmelinii, Betula platyphylla and Populus davidiana). The enrichment, the differences and the variations during growing season of microbial biomass carbon and nitrogen in different rhizosphere soils were analyzed to explore the characteristics of soil microbial biomass and its contribution to soil nutrient pool.[Result] The changes of microbial biomass carbon and nitrogen in the rhizosphere soil of the different species were significant among different months. The microbial biomass carbon content in the rhizosphere soil ranged from 114.14 to 451.05 mg·kg^-1,the microbial biomass nitrogen content in the rhizosphere soil ranged from 40.38 to 185.00 mg·kg^-1. The enrichment rate of microbial biomass carbon in rhizosphere soil was in the order of Pinus sylvestris var. mongolica (87.99%) > Betula platyphylla (78.22%) > Larix gmelinii (73.14%) > Populus davidiana (56.96%). The rank of microbial biomass nitrogen enrichment rate was Populus davidiana (81.50%) > Betula platyphylla (77.63%) > Pinus sylvestris var. mongolica (76.42%) > Larix gmelinii (51.40%). The range of soil microbial biomass carbon-nitrogen ratio was 1.42 to 5.24. The ranges of microbial biomass carbon and nitrogen ratios in the rhizosphere and non-rhizosphere of Pinus sylvestris var. mongolica, Larix gmelinii, Betula platyphylla, and Populus davidiana were 1.42-5.24, 1.57-3.79, 1.67-4.55, 1.55-2.59 and 1.79-3.53, respectively. The average values of soil microbial biomass carbon-nitrogen ratio were 2.64, 2.63, 2.81, 2.11 and 2.36, respectively. The contributions of microbial biomass carbon to the rhizosphere soil organic carbon pool ranged from 0.83% to 0.95%.The contributions of microbial biomass nitrogen to the organic nitrogen pool of rhizosphere soil were between 3.63% and 5.08%.[Conclusion] The content of microbial biomass carbon and nitrogen in the rhizosphere soil of the main cold-temperate mixed forests were significantly higher than those in the non-rhizosphere during the growing season, which indicated that the rhizosphere effect wassignificant. At the end of the growing season, the rhizosphere effects of the coniferous trees were stronger than those of the broad-leaved trees. The conifer species have the greater impact on soil microbial structure and function than the broad-leaved trees.

Key words: Daxing'anling Mountains, soil microbial biomass carbon and nitrogen, rhizosphere soil, rhizosphere effect, dynamic change