Decomposition is an essential process for nutrient recycling. The decomposition of dead plant material is the largest source of nitrogen (N) for plants, and N is the most limiting nutrient for primary productivity in the Northern Hemisphere. The general fate of N during decomposition is well understood in a broad sense, due to extensive studies of litter mass loss and litter N dynamics. However, the relative contribution of litter N to a) mineral N available for plants and b) immobilized N in microbial biomass and further stabilized in soil organic matter pools remains unknown. This understanding is important in the context of reactive N dynamics and global change. Additionally, the effect of soil fauna on the fate of N is not well understood, and has historically been overlooked in studies of litter decomposition. We present here results on litter-N dynamics from an ongoing study conducted in the context of a larger NSF-DEB funded experiment. Isotopically labeled (e.g., 13C and 15N enriched) big bluestem (Andropogon gerardii) litter, the dominant native species at the site, was incubate in October of 2010 inside raised collars, at the Konza tall-grass prairie, located in Kansas. A fauna suppression treatment (naphthalene) was applied to half of the collars. Litter and soils were collected in May and October of 2011. Soils were separated by depths (0-2, 2-5, 5-10, and 10-20 cm) and soil organic matter separated by size and density (e.g., LF, free-OM, mineral associated-OM), and analyzed for N and 15N.
Results/Conclusions
The amount of litter-derived N entering the soil was not influenced by soil fauna; however, there were significantly more exogenous N incorporation in the litter of the suppressed fauna treatment, indicating the importance of fauna to litter N dynamics. Additionally, there were significantly higher amounts of N in the LF and silt associated-OM, in both the 0-2 and 2-5 cm depths, and in the clay associated-OM, in the 0-2 cm depth, in the fauna suppression treatment as compared to the control. Finally, the amount of N recovered in the first 20 cm of soil did not account for the total litter-derived N release , suggesting additional N sinks (e.g. plant matter, and deep soil), which will be the focus of future research. Our study demonstrates that a large fraction (approximately 40%) of N lost through decomposition is stored in the mineral soil and emphasizes the importance of studying soil fauna as a modifier of decay dynamics.