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

Abstract

Abstract. Initial soil development and enhanced nutrient retention are often important underlying environmental factors during primary succession. We quantified the accumulation rates of nitrogen (N) and soil organic matter (SOM) in a 37-year-long chronosequence of Leymus arenarius dunes on the pristine volcanic island Surtsey in order to illuminate the spatiotemporal patterns in their build-up. The Leymus dune area, volume and height grew exponentially over time. Aboveground plant biomass, cover or number of shoots per unit area did not change significantly with time, but root biomass accumulated with time, giving a root / shoot ratio of 19. The dunes accumulated on average 6.6 kg N ha −1 year −1 , which was 3.5 times more than is received annually by atmospheric deposition. The extensive root system of Leymus seems to effectively retain and accumulate a large part of the annual N deposition, not only deposition directly on the dunes but also from the adjacent unvegetated areas. SOM per unit area increased exponentially with dune age, but the accumulation of roots, aboveground biomass and SOM was more strongly linked to soil N than time: a 1 g m −2 increase in soil N led on average to a 6 kg C m −2 increase in biomass and SOM. The Leymus dunes, where most of the N has been accumulated, will therefore probably act as hot spots for further primary succession of flora and fauna on the tephra sands of Surtsey.

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

“…Despite the fact that the median R / S ratio outside the colony was almost three times higher than the upper extreme for cool temperate deserts reported by Mokany et al (2006), it corresponded closely with the mean ratio of 19 reported by (Stefansdottir et al, 2014) for the Leymus area outside the seabird colony. For the grassland inside the colony, the median R / S of 5 did not differ much from the median reported by Mokany et al (2006) for cool temperate grasslands without bird colonies.…”

“…Despite the very sparse aboveground vegetation cover, it became evident during sampling that the unvegetated tephra sand areas were fully colonized by roots. Another study, which took place on and around Leymus dunes in the same area outside the seagull colony, but not within our permanent study plots, found similar dense root distribution (Stefansdottir et al, 2014). Therefore, we can assume that after vegetation establishment the N retention on Surtsey has increased and is now close to the Table 1.…”

“…The lava is partly filled with tephra sand and silt, which originates from eruptions, erosion of the bedrock material and aeolian transport from the mainland. The vegetation on these sandy areas is dominated by Honkenya peploides and Leymus arenaria Stefansdottir et al, 2014). In 1986, a seabird colony of lesser black-backed gulls (Larus fuscus) was established in a confined area on the SW edge of the island (Petersen, 2009), and has been expanding in size ever since.…”

“…Despite previous research showing negative correlations between R / S ratio and nutrient availability in grassland ecosystems (Levang-Brilz and Biondini, 2003;Chu et al, 2006), no such relationship was found on Surtsey, neither inside nor outside the colony. Outside the seabird colony, such a potential relationship might be concealed by the patchiness of the aboveground vegetation, the homogeneous root distribution (Stefansdottir et al, 2014) and the relatively small size of the measurement frames. The combination of these three factors probably explains why we measured several unrealistically high R / S ratios, ranging up to 194.…”

Inoculation with arbuscular mycorrhizal fungi, fertilization and seed rates influence growth and development of lyme grass seedlings in two desert areas in Iceland

“…With time, lyme grass dunes slowly accumulate N from the surrounding area with an extensive root system (Leblans et al 2014, Stefansdottir et al 2014). The buildup of N within the dunes originating from atmospheric deposition averages 0.66 g N m -2 y -1 (Stefansdottir et al 2014) but within seagull colonies the rate of N buildup within lyme grass is much faster or 4.7 g N m -2 y -1 (Leblans et al 2014). Gradually, therefore, lyme grass probably changes from being predominantly N limited to being largely P limited.…”