The soil physical-chemical properties and the soil microbial functional diversity for carbon source utilization may vary depending on plant functional groups and be susceptible to soil surface disturbance. The objective of this study was to assess the effect of plant functional groups on the potential activities of soil microbial communities and to evaluate the association with soil properties under different plant functional groups (grass, Leymus chinensis, forb, and legume) in Songnen steppe. Soil samples were collected in August 2011. Physiological profiles (CLPP) (Biolog Ecoplates^TM) at community levels were measured for each plot to determine the capability of soil microorganisms in utilizing 31 types of carbon source. Furthermore, soil physiochemical properties (pH, electrical conductivity [EC], soil water [SW], soil organic carbon [SOC], total nitrogen [TN], and C : N ratio [C/N]) were determined in rhizosphere soil under different plant functional groups. The results showed that carbon source utilization and microbial metabolic activity increased with time from 36 to 180 hours. There was a significant difference in the soil microbial community structure among plant functional groups. Significant difference was observed in AWCD (the average well color development) (P < 0.001), Shannon-Wiener index (P < 0.001), richness (P = 0.005) and Pielou evenness index (P < 0.001), and they were significantly higher for grass than other functional groups at the latest stage of incubation (P < 0.01). Carbon source utilization was highest for microbial community under grasses, and it was lowest under forbs. The difference in microbial community structure may result in the difference in utilization of the six types of carbon sources. Grasses and Leymus chinensis had higher utilization ability for sugar, amino acids, carboxylic acids, and polymers, and legumes had higher utilization ability for carbon sources except for carboxylic acids. Forbs had highest utilization ability for phenolic compounds but had lower utilization ability for other carbon sources. SOC and TN of the soil were closely associated with the value of AWCD, Shannon-Wiener index, Richness and Pielou evenness index, and EC of the soil was associated with AWCD and richness, while the effect of SW, pH, and C/N were not significant. For further determination of microbial communities under different plant functional groups, Biolog data after 180 h were subjected to redundancy analysis (RDA), and the results showed that TN, SOC, and EC were the most important indices to represent soil quality under the four plants functional groups in this steppe. Carbon source utilization of soil microbial function changed among the four plant functional groups as follows: grass > Leymus chinensis > legume > forb. This result will improve the understanding of the underground carbon cycle and will benefit the grassland management in Songnen steppe by providing a scientific guide for preservation and improvement of soil quality, soil fertility, and nutrient use efficiency, and for enhancing protection of the ecological environment.