Long-term N fertilization altered 13C-labeled fungal community composition but not diversity in wheat rhizosphere of Chinese black soil

Abstract Plant root exudates are considered as critical substrates mediating the interaction between rhizosphere microorganisms and plants. However, little is known about how microbial community response to root exudates under nitrogen (N) fertilization in agroecosystems. Here, we applied stable isotope probing to divide fungi in wheat rhizosphere soil (under 37-year N fertilization regimes) into two biological compartments: 13 C-labeled and 12 C-labeled fungal communities. High-throughput pyrosequencing was followed to characterize the two biological compartments. Long-term N fertilization changed rhizosphere soil physiochemical properties, and increased the quantity of plant root exudates. 13 C-labeled fungi had lower diversity than 12 C-labeled fungi. The fungal communities were predominantly composed of Ascomycota and Basidiomycota in both the 13 C-labeled and 12 C-labeled DNA, and the abundance of those two phyla were higher in 13 C-labeled than that in 12 C-labeled DNA. The Nonmetric Multidimensional Scaling (NMDS) showed that 13 C-labeled and 12 C-labeled fungal communities were distinct from each other. Long-term N fertilization altered fungal communities in 13 C-labeled DNA, with lower abundance of putative fungal pathogens, and higher abundance of Glomeromycota. Although N fertilization significantly decreased 12 C-labeled fungal diversity, no significant differences were detected in 13 C-labeled fungal diversity, indicating the microbial species responses to root exudates and fertilization both influenced fungal diversity. In addition, 13 C-labeled fungal communities were less determined by soil chemical properties than 12 C-labeled fungal communities, based on partial Mantel test. Overall, our results revealed that long-term N fertilization, which increased the quantity of plant root exudates, altered 13 C-labeled fungal community composition, but not changed 13 C-labeled fungal diversity in our studied ecosystem.