Additions of nitrogen and phosphorus do not reduce storage but stability of soil carbon in a northern peatland

Background and aims

Human-induced increases in nitrogen (N) and phosphorus (P) deposition are considered significant threats to soil carbon (C) sequestration in northern peatlands. However, this hypothesis lacks validation with long-term simulation experiments and dating technology, which are crucial for accurately assessing C storage.

Methods

Using accelerator mass spectrometry (AMS) ¹⁴C dating technology, we examined the effect of 13 years N and P additions on soil C storage in a Sphagnum dominated peatland.

Results

AMS ¹⁴C dating showed that apparent soil accumulation rate decreased from 0.94 in control to 0.74 cm yr⁻¹ on average in nutrient addition plots. However, the soil C storage in the past 50 years was not reduced by N or low level of P additions due to accelerated peat decomposition being offset by more belowground biomass inputs. We found that high level of P additions increased C storage significantly (up to 30%). The additions of N, P or their co-addition increased the ratio of soil labile organic C to total organic C, suggesting a potential decrease in stability due to a shift towards less stable C. Comparatively, microbial and enzyme activities were more sensitive to P addition.

Conclusion

The chronic exogenous nutrient enrichment may facilitate C sequestration to some extent, but it could threaten C sink by diminishing the stability of soil C fractions in peatlands in the long run. The contrasting responses of the quality and quantity of C pool to long-term nutrient enrichment may explain the underlying mechanisms of C dynamics in peatlands.