Mixed plantation forest litter improves microbial nitrogen transformation by increasing nitrogen metabolism related genes and key bacterial taxa in northern China

Abstract Nitrogen (N) metabolism is a key metabolic pathway of nutrient cycling in forest ecosystems. However, the mechanisms by which mixed plantation forest litter improves microbial N transformation are poorly understood. Thus, we investigated the N characteristics, N metabolism‐related genes, and key microbial modules of litter and soil in three types of forests: coniferous (CP forest), broadleaf (BP forest), and mixed forests (MCBP forest). Results indicated that the total N (TN), total hydrolysable organic N (THON), and percentage values of NH 4 + ‐N/TN and NO 3 − ‐N/TN in BP forest and MCBP forest litter were higher than those of CP forest litter, which was attributed to the increase in abundance of N fixation genes and dissimilatory nitrate reduction genes. The MCBP forest increased the bacterial number and diversity, and the abundance of key bacterial taxa. Bacterial key modules 1 and 2 were identified, consisting of Acidobacteria, Actinobacteria, Chloroflexi, Nitrospirae, Proteobacteria, and Gemmatimonadetes, while archaeal module 5 was also a key module, comprising Thaumarchaeota and Euryarchaeota. Nutrients were the limiting factor of key microbial modules in the decomposition of litter, further influencing N metabolism‐related genes and enzymes. Therefore, mixed plantation forests increased microbial N fixation and transformation during litter decomposition in northern China.