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 relationship between N accumulation and biomass and ecosystem carbon (C) stocks in a 50-year-old volcanic island, Surtsey, Iceland, where N stocks are still exceptionally low. However, a 28-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 had accumulated 0.7 kg N ha −1 yr −1 , which was ca. 50-60 % of the estimated N input rate from wet deposition. This approximates values for systems under low N input and bare dune habitats. 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 ton C ha −1 ) had reached normal values for grasslands, while the soil organic carbon (SOC) stocks (4-10 ton 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.

Up, up and away: bird‐mediated ectozoochorous dispersal between aquatic environments

“…Seed adhesion to seabirds is believed to contribute to the LDD and SDD of plant propagules between islands (Walker, 1991;Burger, 2005;Aoyama et al, 2012). Seabirds probably played a role in the colonisation by vascular plant species of the young volcanic island Surtsey, near Iceland (Sigurdsson & Magn usson, 2010;Leblans et al, 2014;Magn usson et al, 2014). Thus, birds can be viewed as engineers that modify ecosystem structure and function through transfer of dispersal units (Ellis, 2005;Sigurdsson & Magn usson, 2010).…”

Organic matter quantity and source affects microbial community structure and function following volcanic eruption on Kasatochi Island, Alaska

“…In volcanic soils, the accumulation of OM proceeds rapidly in the first decades following deposition of parent material (Zehetner, 2010). In addition to the positive feedback between biological weathering and C accumulation already discussed, positive feedback between bird-imported marine N and plant and microbial production is likely (Croll et al, 2005;Leblans et al, 2014), especially because plant production on Kasatochi Island is N-limited (Michaelson et al, 2014). In addition to the positive feedback between biological weathering and C accumulation already discussed, positive feedback between bird-imported marine N and plant and microbial production is likely (Croll et al, 2005;Leblans et al, 2014), especially because plant production on Kasatochi Island is N-limited (Michaelson et al, 2014).…”

“…In this study, mean %C in the pyroclastic deposits with bird, plant, and bird and plant OM inputs was similar, 40% higher and 500% higher, respectively, than bare pyroclastic materials (Table S1). In addition to the positive feedback between biological weathering and C accumulation already discussed, positive feedback between bird-imported marine N and plant and microbial production is likely (Croll et al, 2005;Leblans et al, 2014), especially because plant production on Kasatochi Island is N-limited (Michaelson et al, 2014). There were also significantly higher bacterial populations in pyroclastics with bird inputs relative to pyroclastics with plant inputs and similar %C (Fig.…”

“…Vectors of cell dispersal for colonization may include long-distance atmospheric deposition, local aeolian redistribution of sediment (Sabacka et al, 2012;Smith et al, 2013) or colonizing plants and animals that carry microbiota on their tissues or in their guts. Energy and nutrients may be provided by animal-borne inputs of OM (Croll et al, 2005;Leblans et al, 2014), or newly fixed carbon (C) from plant photosynthesis (Halvorson et al, 1992;Ibekwe et al, 2007;Halvorson and Smith, 2009). In the absence of OM input from external sources to drive microbial heterotrophy, microbial photo-or chemolithoautotrophy must fuel cell growth (King, 2003;Nemergut et al, 2007).…”

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.…”