COS 51-3 - Legacy effects of nitrogen fertilization on Miscanthus-associated microbial activity.

Abstract: Continuous application of excessive nitrogen fertilizers harms the sustainability of agroecosystems largely by altering the activity of plant-associated microbiomes. However, how historical nitrogen addition alters the microbial response to subsequent nitrogen fertilizers remains unclear. We hypothesized that microbes previously exposed to long-term N fertilizer application would respond to reapplication of N fertilizer more intensively than microbes that had not previously received fertilizer. Soil samples were collected from a Miscanthus field where different levels of historical nitrogen fertilization (0, 60, and 120 kg nitrogen-urea ha^-1) were applied annually from 2008 to 2015, and reapplied with plot-specific rates in 2021. Potential assays and amplicon sequencing were conducted for key nitrogen cycling processes such as nitrification, denitrification, and N fixation. Here we showed that despite six years of discontinuation, historical nitrogen stimulated nitrification and denitrification response to short-term nitrogen addition. In comparison, this rapid response to added N was not observed in previously unfertilized soils. Moreover, while long-term historical nitrogen addition led to lower relative abundance of diazotrophs in rhizosphere soil, short-term contemporary nitrogen addition did not exhibit significant influence on the composition of soil microbial communities. In conclusion, this study demonstrated that the legacy effects of long-term nitrogen addition mediated the short-term microbial response to nitrogen addition, which has great implications for future nutrient management and sustainability for Miscanthus.