Anthropogenic nitrogen enrichment enhances soil carbon accumulation by impacting saprotrophs rather than ectomycorrhizal fungal activity

• Published in: Global Change Biology
• Main Authors: Maaroufi, Nadia I., Nordin, Annika, Palmqvist, Kristin, Hasselquist, Niles J., Forsmark, Benjamin, Rosenstock, Nicholas P., Wallander, Håkan, Gundale, Michael J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley-Blackwell 2019
• Subjects: Soil Science; carbon sequestration; ecological stoichiometry; Gadgil effect; high-throughput sequencing; ingrowth mesh bags; ITS amplicons; litter decomposition; root exclosure; soil organic matter; Northern Sweden
• Online Access: https://lup.lub.lu.se/record/5d9270ac-9ad9-40ba-8f74-9b4b65b78306; https://doi.org/10.1111/gcb.14722

There is evidence that anthropogenic nitrogen (N) deposition enhances carbon (C) sequestration in boreal forest soils. However, it is unclear how free-living saprotrophs (bacteria and fungi, SAP) and ectomycorrhizal (EM) fungi responses to N addition impact soil C dynamics. Our aim was to investigate how SAP and EM communities are impacted by N enrichment and to estimate whether these changes influence decay of litter and humus. We conducted a long-term experiment in northern Sweden, maintained since 2004, consisting of ambient, low N additions (0, 3, 6, and 12 kg N ha−1 year−1) simulating current N deposition rates in the boreal region, as well as a high N addition (50 kg N ha−1 year−1). Our data showed that long-term N enrichment impeded mass loss of litter, but not of humus, and only in response to the highest N addition treatment. Furthermore, our data showed that EM fungi reduced the mass of N and P in both substrates during the incubation period compared to when only SAP organisms were present. Low N additions had no effect on microbial community structure, while the high N addition decreased fungal and bacterial biomasses and altered EM fungi and SAP community composition. Actinomycetes were the only bacterial SAP to show increased biomass in response to the highest N addition. These results provide a mechanistic understanding of how anthropogenic N enrichment can influence soil C accumulation rates and suggest that current N deposition rates in the boreal region (≤12 kg N ha−1 year−1) are likely to have a minor impact on the soil microbial community and the decomposition of humus and litter.