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

Abstract

Abstract. 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 are 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−1 yr−1, which was ca. 60% of the estimated N input rate from wet deposition. The seagulls have added, on average, 47 kg N ha−1 yr−1, 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−1) had reached normal values for grasslands, while the soil organic carbon stocks (SOC; 4–10 kg C ha−1) 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.

Accumulation of nitrogen and organic matter during primary succession of <i>Leymus arenarius</i> dunes on the volcanic island Surtsey, Iceland

“…50 kg N ha −1 year −1 (Leblans et al, 2014). Elsewhere on the island, where the sparse Leymus and Honckenya community is dominant, the average SON accumulation rate is ca.…”

“…Relatively large amounts of plant roots were, however, present in all soil samples taken among Leymus dunes in this area ( Fig. 3b; Leblans et al, 2014). These roots are most likely to originate from the scattered Leymus dunes and can translocate nutrients and water into the dunes.…”

“…6 times higher than on average in the soil of same area on Surtsey (Leblans et al, 2014). There are several possible explanations for this difference: (i) translocation of N into the dunes from the unvegetated areas around with root transport, (ii) accumulation of N with wind-blown organic material that is trapped by the dunes, (iii) more N being transported by birds to dunes than to other areas, (v) free-living N fixation of soil bacteria within the dunes, or (vi) symbiotic N fixing with Leymus or Honckenya.…”

“…Elsewhere on the island, where the sparse Leymus and Honckenya community is dominant, the average SON accumulation rate is ca. 1 kg N ha −1 year −1 (Leblans et al, 2014), which is about half of the expected atmospheric N deposition of areas in Iceland with annual precipitation of 1500 mm (1.8-2.0 kg N ha −1 year −1 ; Gíslason et al, 1996;Sigurðsson et al, 2005).…”

Colonization of an empty island: how does a plant with a plastic gender system respond?

“…Pistillate plants allocated more to below-soil surface biomass and they were more tolerant of water stress (Sánchez-Vilas and Retuerto, 2009; Sánchez-Vilas et al, 2012). H. peploides possesses an extensive network of roots well adapted to exploit the limited nutrients and water that percolate easily in the gravelly substratum (Leblans et al, 2014). Intraspecific competition for soil resources could be strong whereas competition for light may play a minor role, as we rarely observed individuals making interwoven canopies.…”