ObjectiveIn order to study the characteristics of soil microbial biomass carbon and nitrogen in natural Pinus sylvestris var. mongolia forest in the cold temperature zone, the dynamic variation rule of soil microbial biomass carbon and nitrogen and those influencing factors were analyzed to provide a theoretical basis for soil nutrient transport and flow characteristics in the natural Pinus sylvestris var. mongolia forest.

MethodMeasurements were taken every month from May to September in 2017 at three sites, including the top, the middle, the lower regions of slope in the Pinus sylvestris var. mongolia forest. The microbial biomass carbon and nitrogen in the 0−10 cm and 10−20 cm were determined by chloroform fumigation and extraction method, with their seasonal dynamics and the relationships with soil physicochemical properties in three sites.

ResultThe results showed that the soil microbial biomass carbon and nitrogen contents under different slope positions presented fluctuating downward trends from May to September, with the ranges of 74.33 to 515.33 mg/kg and 15.33 to 240.57 mg/kg, respectively. The microbial biomass carbon-nitrogen radio was between 1.04 and 5.73, which was significantly different among varied site conditions during the measuring periods. The mean values of soil microbial biological carbon and nitrogen in the lower and middle regions of slopes were significantly higher than those in the top regions of slope (P < 0.05). Site conditions had significant effects on soil microbial biomass carbon, nitrogen and soil microbial biomass carbon-nitrogen ratio (P < 0.01). The soil microbial biomass carbon and nitrogen contents in 0−10 cm soil layer were significantly larger than those in 10−20 cm soil layer. Soil microbial biomass carbon and nitrogen were significantly positively correlated with soil total organic carbon, total nitrogen and soil water content, but not correlated with soil temperature and pH.

ConclusionThe study shows that slope position has significant influence on soil microbial biomass in the Pinus sylvestris var. mongolia forest in the cold temperature zone, and its content has obvious site-differentiation rule. Soil total organic carbon, total nitrogen and soil water content are the main influencing factors leading to soil microbial biomass carbon and nitrogen difference.