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Here, we present evidence that ca. 20 years of experimental N deposition altered the composition of lignin-decaying class II peroxidases expressed by forest floor fungi, a response which has occurred concurrently with reductions in plant litter decomposition and a rapid accumulation of soil organic matter. This finding suggests that anthropogenic N deposition has induced changes in the biological mediation of lignin decay, the rate limiting step in plant litter decomposition. Thus, an altered composition of transcripts for a critical gene that is associated with terrestrial C cycling may explain the increased soil C storage under long-term increases in anthropogenic N deposition. IMPORTANCE Fungal class II peroxidases are enzymes that mediate the rate-limiting step in the decomposition of plant material, which involves the oxidation of lignin and other polyphenols. In field experiments, anthropogenic N deposition has increased soil C storage in forests, a result which could potentially arise from anthropogenic N-induced changes in the composition of class II peroxidases expressed by the fungal community. In this study, we have gained unique insight into how anthropogenic N deposition, a widespread agent of global change, affects the expression of a functional gene encoding an enzyme that plays a critical role in a biologically mediated ecosystem process. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitrogen (N) deposition decreases AMF root infection and mycelial production. [•] We examined effects of increased N on the active soil AMF community using rRNA. [•] Active AMF community composition was not affected by increased N deposition. [•] Increased soil N decreased abundance of a close relative of Glomus intraradices. [•] Significant decrease in rare taxa under increased experimental N deposition. [ABSTRACT FROM AUTHOR]

Global increases in the rate of atmospheric N deposition have the potential to alter the composition and function of soil microbial communities. Here, we tested the hypothesis that experimental N deposition has altered the composition of active communities of Dikarya fungi. Such a change may underlie previously observed reductions in decomposition and increases in soil organic matter in a long-term field experiment. The actively metabolizing forest floor fungal community was characterized from cDNA clone libraries constructed from 28S fungal rRNA extracted from the forest floor of two northern hardwood stands in the lower peninsula of Michigan. We demonstrate that long-term experimental N deposition altered the composition of the active communities of Dikarya fungi in the forest floor in each of these forest stands. Because forest floor fungi are important decomposers, the alteration of forest floor fungal communities by increasing N deposition may have implications for the cycling and storage of C in forest ecosystems. [ABSTRACT FROM AUTHOR]