Carbon (C) cycling in terrestrial ecosystems is driven by the decomposition of plant litter, a process that is mediated by saprotrophic microbial communities. Increased nitrogen (N) deposition alters microbial community composition and decreases activity, often with a concurrent increase in soil organic matter (SOM). Most studies that examine saprotrophic communities focus on plant leaf decay, but recent evidence has suggested that fine roots may be a dominant source of SOM in soils. In our long-term experimental N deposition study, we have seen an increase in SOM (+18%) which is biochemically similar to fine roots. To test whether saprotrophic communities that decay roots are altered by N deposition, we incubated bags containing dead fine roots in our experimental N deposition sites and harvested them at 4 and 12 months. We then extracted the DNA and used high throughput sequencing to examine the fungal communities using the 28S rRNA gene.
Results/Conclusions
Fungal communities from the root incubation bags responded significantly to experimental N deposition at both time points (PERMANOVA; P < 0.004, P<0.003), wherein richness and diversity generally increased under experimental N deposition. Six fungal classes represented the majority of the fungal communities, with Agaricomycetes alone accounting for an average of ~40% of the sequences. Three of these classes responded significantly to experimental N deposition at 4 months: Eurotiomycetes (+2.6), Agaricomycetes (-12%), and Tremellomycetes (+4%); only Tremellomycetes significantly increased (+6%) after 12 months.
Our results suggest that shifts from experimental N deposition in fungal taxa that decompose roots may have long-lasting consequences for C cycling and storage. As Agaricomycetes represented the overwhelming majority of our fungal community, this group may play a key role in root decomposition. Furthermore, it was negatively impacted by experimental N deposition, indicating it may be important for SOM accumulation as anthropogenic N deposition continues into the future.