Freeze-thaw cycles are the key drivers of soil carbon cycling in cold zone ecosystems. Recent theoretical and empirical work suggests that roots enhance the sequestration of soil carbon and the stability of soil microbial biomass. The rhizosphere-the layer of soil influenced by plant roots-is considerably richer in microbial diversity than the surrounding bulk soil. However, the effects of roots on microbial ecological processes and the potential mechanisms remain unclear. Investigating the effects of rhizosphere microbial changes in soils without roots in the northeast forests can therefore provide scientific support for vegetation restoration and ecological reconstruction in this region. This study focused on the changes in microbial biomass in forest soils without plant roots in the Xiaoxing'an Mountains during the freeze-thaw cycle. The experiment was conducted in six typical forest types:virgin mixed broadleaved-Korean pine (Pinus koraiensis) forest, spruce-fir (Picea koraiensis-Abies nephrolepis) valley forest, secondary birch (Betula platyphylla) forest, Korean pine plantation, and Dahurian larch (Larix gmelinii) plantation. In 2010, we randomly selected three plots (20 m×30 m) each of which contained three root-trenched subplots (2 m×2 m) in each forest type. Soil samples from 0-10 cm and 10-20 cm soil layers were randomly selected weekly in the six forest types from April to May 2013 (the freeze-thaw cycle). We used trenching methods, randomly set three subplots (2 m×2 m) without roots inside of each 20 m×30 m plot. Furthermore, we randomly set three (2 m×2 m) control plots; with the root resection plots about 1 m apart. We measured the variability of rhizosphere microbial biomass in different soil layers associated with six forest types during the freeze-thaw cycle. We preformed the fumigation-extraction method to collect samples, and used the Analytic Jena 3000 to analyze soil microbial carbon and nitrogen contents. We observed significant differences in soil microbial biomass and soil nutrient stability between the root resection and control plots. The microbial biomass carbon (MBC) of the root resection plots was significantly different than that of the control plots. However, no significant difference was observed in microbial biomass nitrogen (MBN) between these two treatments in each forest type (P>0.05). In the control plots, the MBC was significantly negatively correlated with soil organic carbon, and total nitrogen (P<0.05); MBC, MBN, and the microbial carbon and nitrogen ratio (MBC/MBN) were all significantly positively related to temperature; and soil water content between MBC, MBN, and MBC/MBN were not significantly different. In the root removal plots, MBC and soil temperature had a significant negative correlation, and the influence of soil organic carbon and total nitrogen were not significant (P>0.05) on MBC, MBN, and MBC/MBN. Our results suggest that forest areas lacking root and soil protection would see reductions in soil MBC, and the microbial biomass sequestration in these forest soils would be negatively influenced during the freeze-thaw cycle. The capacity of rhizobacteria to metabolize carbon sources was stronger in communities associated with roots than without roots. Our results also suggest that rhizobacteria from associated species have distinct carbon metabolism characteristics.