Experimental N addition across a N deposition gradient

Fungal decomposition of soil organic matter is partly driven by soil nitrogen (N) availability. This ecosystem process is being jeopardized by changes in N inputs that have resulted from a tripling of atmospheric N deposition in the last century. Soil fungi are impacted by atmospheric N deposition as community composition shifts due to higher N availability, as soils are acidified, or as micronutrients become increasingly limiting. Fungal communities that persist with chronic N deposition may be enriched with traits that enable them to tolerate environmental stress, which may trade-off with traits enabling organic matter decomposition. We hypothesized that fungal communities would respond to N deposition by shifting community composition and functional gene abundances toward those that tolerate stress but are weak decomposers. We sampled soils at seven eastern US hardwood forests where ambient N deposition varied from 3.2 – 12.6 kg N ha-1 y-1, five of which also have experimental plots where atmospheric N deposition was simulated through fertilizer application treatments (25 – 50 kg N ha-1 y-1). We found that fungal community and functional responses to chronic fertilizer treatments varied across the ambient N deposition gradient.