Abstract
Saprotrophic fungi are the primary decomposers of plant litter in temperate forests, and their activity is critical for carbon (C) and nitrogen (N) cycling. Simulated atmospheric N deposition is associated with reduced fungal biomass, shifts in fungal community structure, slowed litter decay, and soil C accumulation. Although rarely studied, N deposition may also result in novel selective pressures on fungi, affecting evolutionary trajectories. To directly test if long‐term N enrichment reshapes fungal responses to N, we isolated decomposer fungi from a long‐term (28 yr) N‐addition experiment and used a common garden approach to compare growth rates and decay abilities of isolates from control and N‐amended plots. Both growth and decay were significantly altered by long‐term exposure to N enrichment. Changes in growth rates were idiosyncratic, as different species grew either more quickly or more slowly after exposure to N, but litter decay by N isolates was consistent and generally lower compared to control isolates of the same species, a response not readily reversed when N isolates were grown in control (low N) environments. Changes in fungal responses accompany and perhaps drive previously observed N‐induced shifts in fungal diversity, community composition, and litter decay dynamics.