Effects of activated carbon source on soil nitrogen content in three land use types in middle Guizhou, China, and the underlying mechanisms

Abstract Reducing fertilizer use while enhancing efficiency through microbial pathways is a promising approach for agricultural development. The application of an activated carbon source can influence soil nitrogen levels by modulating microbial communities; however, the responses of nitrogen cycle pathways to exogenous carbon sources remain unclear. This study examined soils from three land use types (paddy fields, dry land, and tea plantations) in Anshun, Guizhou, China. Field experiments were conducted using three application rates of activated carbon (glucose): 0.0, 5.0, and 10.0 g per kilogram of soil. The effects of glucose on soil physicochemical properties, microbiota composition, and nitrogen cycle-related genes were analyzed by assessing soil properties and 16S rDNA sequences. The results showed that, after the addition of glucose, the total nitrogen contents of the three types of soils were generally higher than those of the corresponding control treatments. Glucose addition significantly increased the relative abundances of Azotobacter in paddy field and dry land soils and Sporolactobacillus in tea plantation soil. Across all land use types, the highest relative abundance of nif genes was observed in soils treated with 10.0 g of glucose. Glucose application suppressed soil nitrification and promoted the reduction of assimilated nitrate, with effects proportional to the glucose load. In response to glucose addition, the relative abundances of denitrification pathway genes tended to increase in paddy field soil; these abundances exhibited minimal changes in dry land soil and significantly decreased in tea plantation soil. The above results suggest that, in different land use types, the addition of glucose can activate specific dominant nitrogen cycle microbial combinations, thereby regulating the nitrogen transformation rates in each land use type. These results provide theoretical and empirical support for understanding the impact and mechanisms of exogenous activated carbon on soil nitrogen content in Middle Guizhou, China, thereby offering insights and strategies for efficient nitrogen utilization in this region. Graphical abstract