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Research article2019Peer reviewed

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

Maaroufi, Nadia, I; Nordin, Annika; Palmqvist, Kristin; Hasselquist, Niles J.; Forsmark, Benjamin; Rosenstock, Nicholas P.; Wallander, Hakan; Gundale, Michael J.

Abstract

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.

Keywords

carbon sequestration; ecological stoichiometry; Gadgil effect; high-throughput sequencing; ingrowth mesh bags; ITS amplicons; litter decomposition; root exclosure; soil organic matter

Published in

Global Change Biology
2019, Volume: 25, number: 9, pages: 2900-2914