The National Ecological Observatory Network (NEON) collects a large suite of co-located ecological data using standard methodology and anticipates operating for 30 years. One of the strengths of NEON data is that diverse ecological data are collected from the same 47 terrestrial sites and 34 aquatic sites. Here, we examine a subset of NEON data products from terrestrial sites which can be leveraged to provide multi-response critical loads of atmospheric deposition: namely soil C:N, available soil nitrogen, soil microbe biomass (by PLFA), aboveground herbaceous plant productivity, and root biomass and chemistry.

The NEON terrestrial sites span a nitrogen (N) deposition gradient of 2.0 to 10.9 kg/ha/yr. The increase in N deposition across the spatial gradient of sites had a significant negative correlation with soil C:N ratio in the mineral horizon, a positive correlation with fine root mass in the 1-2 mm size class, and a negative correlation with fine root percent nitrogen in the 1-2 mm and 2-10 mm size classes. Available soil nitrogen, soil microbial biomass (total lipids from PLFA analysis), and above-ground herbaceous productivity (of N-fixers and summed across all functional groups) were not correlated with nitrogen deposition.

Using an existing gradient of atmospheric deposition and data from the first 7 years of NEON sampling, we identified emergent spatial patterns in soil chemistry, root biomass, and root chemistry. Other responses such as microbial community composition and aquatic chemistry could also be examined using these and other NEON datasets, and by examining the impact of climatic gradients that also exist across NEON sites. With additional work, it may be possible to derive critical loads from a suite of these response surfaces.

¹ National Ecological Observatory Network, Boulder, CO

² U.S. Environmental Protection Agency, Washington, DC

*Corresponding author: ssimkin@battelleecology.org