Application of nitrogen fertilizer to a boreal pine forest has a negative impact on the respiration of ectomycorrhizal hyphae
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There is evidence that increased N inputs to boreal forests, via atmospheric deposition or intentional fertilization, may impact negatively on ectomycorrhizal (ECM) fungi leading to a reduced flux of plant-derived carbon (C) back to the atmosphere via ECM. Our aim was to investigate the impact of N fertilization of a Pinus sylvestris (L.) forest stand on the return of recently photoassimilated C via the ECM component of soil respiration.
We used an in situ, large-scale, 13C-CO2 isotopic pulse labelling approach and monitored the 13C label return using soil gas efflux chambers placed over three different types of soil collar to distinguish between heterotrophic (RH), autotrophic (RA; partitioned further into contributions from ECM hyphae and total RA) and total (RS) soil respiration.
The impact of N fertilization was to significantly reduce RA, particularly respiration via extramatrical ECM hyphae. ECM hyphal flux in control plots showed substantial spatial variability, resulting in mean flux estimates exceeding estimates of total RA, while ECM contributions to RA in N treated plots were estimated at around 30%.
Significant impacts on soil C cycling may be caused by reduced plant C allocation to ECM fungi in response to increased N inputs to boreal forests; ecosystem models so far lack this detail.
Keywords13CO2 Pulse labelling Soil CO2 efflux Ectomycorrhizas Soil respiration Boreal forest
Analysis of variance
Continuous-flow isotope ratio mass spectrometer
Autotrophic soil respiration
Heterotrophic soil respiration
This study was supported by grants from SLU, the Kempe Foundations, the research councils VR and FORMAS (to P.H.) and the UK Natural Environment Research Council (NERC grant ref.NE ⁄ E004512 ⁄ 1). We are grateful to Sylvia Toet (York) for loan of the CO2 flux chamber as well as to Toby Gass, Erica Nocchi, Sonja Keel and other members of the CANIFLEX team for assistance in the field.
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