Abstract: The Sanjiang Plain is the largest distribution area of marsh wetlands in China. Over the past 60 years, the land use patterns in the Sanjiang Plain have changed, and the soil physicochemical and biological properties have also been significantly affected. To clarify the differences in soil physicochemical properties and soil microbial functional activity under different land use patterns in Sanjiang Plain, we collected soil samples from 0-10 cm and 10-20 cm layer of cropland, forest, and wetland in the Nongjiang River Basin of Sanjiang Plain. Employing Biolog-ECO microplate technology, we analyzed soil microbial carbon source metabolic activity, carbon source utilization characteristics and functional diversity, and explored the effects of soil physicochemical properties on soil microbial carbon source metabolic activity under different land use patterns by using structural equation modeling (SEM). The results showed that soil microbial carbon source metabolism ability in 0-10 cm soil layer of forest was significantly higher than that of wetland and cropland. The carbon source metabolic activity in 10-20 cm soil layer of forest and wetland was higher than that of cropland. Soil microbial Shannon index, Simpson index, and McIntosh index were positively correlated with soil total carbon, dissolved organic carbon, microbial biomass carbon, total nitrogen, microbial biomass nitrogen, ammonium nitrogen and nitrate nitrogen contents. After reclamation of wetland into cropland, the utilization ratio of amino acids by soil microorganisms was increased, while the utilization ratio of polymers was reduced. SEM results showed that soil microbial biomass carbon, ammonium nitrogen, total carbon, nitrate nitrogen, moisture content, and pH value were important factors affecting soil microbial carbon source metabolic activity.

Key words: wetland, land use pattern, carbon source utilization, microbial diversity, Biolog-ECO, structural equation modeling