Abstract:Soil microbe is the most important decomposer in forest ecosystems and sensitive indicator to environmental changes. It plays a crucial role in forest carbon and nitrogen cycles. However, few studies on soil microbial biomass carbon (Cmic) and nitrogen (Nmic) have been conducted in the temperate forests of northeastern China. In this study, we used a fumigation-extraction method (FE) to examine seasonal dynamics of Cmic and Nmic and vertical changes along soil profiles in representative temperate forests in this region. The experimental design included five forest types, three 20 m×30 m plots in each forest type. The forest types were Dahurian larch (Larix gmelinii) plantation, Korean pine (Pinus Koraiensis) plantation, Mongolian oak (Quercus mongolica) forest, aspen-birch forest (dominated by Populus davidiana and Betula platyphylla), and hardwood forest (dominated by Fraxinus mandshurica, Juglans mandshurica and Phellodendron amurense). In each plot, we randomly took soil samples by two soil layers (0-10 cm and 10-20 cm) from five spots every month from March to November of 2008. The samples in each plot were mixed as one sample for Cmic and Nmic determination. All soil samples were stored at 2 ℃ before analyzed within one week from sampling. The Cmic and Nmic were significantly different (P < 0.01) among the forest types. The Cmic in the Dahurian larch, Korean pine, Mongolian oak, aspen-birch, and hardwood forests varied from 278-937, 218-1020, 313-891, 510-1092, and 440-1911 mg kg-1, respectively, while the Nmic varied from 18-72, 18-103, 24-95, 43-125, and 40-208 mg kg-1, respectively. Both Cmic and Nmic decreased with the soil depth increasing for all forests. Overall, the Cmic and Nmic showed similar seasonal patterns for all forests, in which they decreased before the growing season commenced, increased in the end of the growing season, and had 1-2 in-between peaks. However, the values and occurring times of the peaks varied with forest types and soil layers. The seasonal variations in the Cmic and Nmic were greater at the 0-10 cm soil layer than those at 10-20 cm. The Cmic and Nmic were significantly positively correlated with the leaf litterfall, soil organic carbon content and total soil nitrogen content. The Cmic was positively correlated with soil water content, but negatively with soil temperature. We concluded that the variations in litterfall amount and composition, soil physical and chemical properties among the forest types mainly contributed to the differences in spatio-temporal patterns of the soil microbial biomass in the five forests.