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.