Effects of seabird nitrogen input on biomass and carbon accumulation after 50 years of primary succession on a young volcanic island, Surtsey

N. I. W. Leblans, B. D. Sigurdsson, P. Roefs, R. Thuys, B. Magnússon, I. A. Janssens
2014 Biogeosciences Discussions  
What happens during primary succession after the first colonizers have occupied a pristine surface largely depends on how they ameliorate living conditions for other species. For vascular plants the onset of soil development and associated increase in nutrient (mainly nitrogen, N) and water availability is especially important. Here, we report the relation between N accumulation and biomass- and ecosystem carbon (C) stocks in a 50 year old volcanic island, Surtsey, in Iceland, where N stocks
more » ... still exceptionally low. However, 27 year old seagull colony on the island provided nutrient-enriched areas, which enabled us to assess the relationship between N stock and biomass- and ecosystem C stocks across a much larger range in N stock. Further, we compared areas on shallow and deep tephra sands as we expected that deep-rooted systems would be more efficient in retaining N. The sparsely vegetated area outside the colony was more efficient in N retention than we expected and had accumulated 0.7 kg N ha<sup>−1</sup> yr<sup>−1</sup>, which was ca. 60% of the estimated N input rate from wet deposition. The seagulls have added, on average, 47 kg N ha<sup>−1</sup> yr<sup>−1</sup>, which induced a shift from belowground to aboveground in ecosystem N and C stocks and doubled the ecosystem "N use efficiency", determined as the ratio of biomass and C storage per unit N input. Soil depth did not significantly affect total N stocks, which suggests a high N retention potential. Both total ecosystem biomass and C stocks were strongly correlated with N stock inside the colony, which indicated the important role of N during the first steps of primary succession. Inside the colony, the ecosystem biomass C stocks (17–27 kg C ha<sup>−1</sup>) had reached normal values for grasslands, while the soil organic carbon stocks (SOC; 4–10 kg C ha<sup>−1</sup>) were only a fraction of normal grassland values. Thus, it will take a long time until the SOC stock reaches equilibrium with the current primary production; during which conditions for new colonists may change.
doi:10.5194/bgd-11-6269-2014 fatcat:s2da4bzq3nfp7j3s4lkthfrcyq