Þráðormasamfélög Surtseyjar 50 árum eftir myndun hennar.

Soil nematodes are a key group that can both influence and reflect changes in the soil ecosystem. We investigated the generic composition, abundance and community structure of soil nematodes in two contrasting vegetation successional seres now found on the 50 year old volcanic island of Surtsey, Iceland. One represented the primary succession without much external input of nutrients (S1), while the other was a grassland that has evolved under a strong influence of allochthonous nutrient inputs by gulls (S2). In 2012 in total 25 genera of nematodes were identified, of which 14 were reported on Surtsey for the first time. Across the whole island, the nematode abundance and distribution was most strongly related to soil C:N ratio, soil acidity, plant cover and biomass. The nematode abundance was higher at S2 and there the trophic structure was dominated by bacterial- and plantfeeders, while hyphal-feeders were more dominant at S1. Nematode communities have continued to change at S1 since the last nematode survey, which took place 17 years ago, even where the vegetation cover and composition has remained stable. This may indicate a gradual change in the soil environment at S1. Within S2, the nematode community had become denser and more structured, but still it had lower generic diversity than found at S1. Resource availability was found to be an important driver for nematode colonization and primary succession on this isolated volcanic island. However, the study also found that soil nematode communities may show a different pattern of succession than plant communities.Samfélög þráðorma í jarðvegi gegna mikilvægu hlutverki í frumframvindu og jarðvegsmyndun. Í þessari grein var fjallað um þær breytingar sem hafa orðið á samfélögum þráðorma í jarðvegi á Surtsey síðan að hún myndaðist 1963. Megin áherslan var lögð á að bera saman fjölda ættkvísla, þéttleika og skiptingu þeirra í fæðuhópa á milli tveggja megin framvindustiga gróðurs á Sutsey; á svæðum með lítilli næringarefnaákomu (S1) og svæðum innan þétts máfavarps á eynni þar sem næringarefnaákoma er mikil og gróðurframvinda er lengra komin (S2). Alls fundust 25 ættkvíslir þráðorma í þessari rannsókn og 14 þeirra höfðu ekki fundist áður á Surtsey. Þegar öll gögnin voru skoðuð saman kom í ljós að bæði þéttleiki og samsetning þráðormasamfélaga sýndi sterkast samband við C:N hlutfall í jarðvegi, sýrustig jarðvegs, gróðurþekju og ofanjarðarlífmassa gróðurs. Þéttleiki þráðorma var hærri á S2 og bakteríu- og plönturótaætur einkenndu samfélögin þar á meðan sveppþráðaætur einkenndu samfélögin á S1. Þráðormasamfélögin á S1 höfðu breyst frá síðustu úttekt þar fyrir 17 árum, þrátt fyrir að gróðurþekja og samsetning gróðurs hafi ekki breyst þar. Þetta bendir til breytinga (framvindu) á jarðvegsþáttum sem ekki sér merki ofanjarðar. Á S2 höfðu þráðormasamfélögin á sama tíma orðið þéttari og 44 ICELANDIC AGRICULTURAL SCIENCES með flóknari fæðuvef, en fjölbreytileiki þeirra var samt minni en á S1. Næringarefnaákoma, gróðurframvinda og jarðvegsmyndun voru afgerandi þættir í frumframvindu þráðorma. Athygli vakti einnig að framvinda þráðorma hafði að hluta til annan feril en gróðurframvinda á SurtseyPeer ReviewedRitrýnt tímari

The pathogenicity of the blue stain fungus Ophiostoma clavatum in Scots pine seedlings

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Þéttleiki og samfélög fugla á svæðum sem hafa verið grædd upp með framandi eða innlendum plöntutegundum

This paper was prepared as a part of the M.Sc. thesis of the first author at the Agricultural University of Iceland. We are grateful for the contribution of The Icelandic Soil Conservation Service, Náttúrusjóður Pálma Jónssonar and Kvískerjasjóður to this project. We thank the employees of The Icelandic Soil Conservation Service and Icelandic Institute of Natural History who contributed with their help and advice.Degradation of ecosystems and introductions of invasive species pose a threat to global biodiversity. Ecosystem restoration and revegetation actions are important for amending habitat loss and for the protection of species of plants and animals. Iceland has the highest rate of soil erosion and desertification in Northern Europe and counteractions to erosion and revegetation measures have taken place for over a century. We studied the effect of revegetation on the density and composition of birds and invertebrate abundance in 26 survey areas comparing: a) unvegetated eroded areas, b) native heathlands restored on eroded land, and c) revegetation by the introduced and exotic Nootka lupin (Lupinus nootkatensis) on eroded land. Birds were counted on transects and invertebrates sampled with a sweep net. Both revegetation methods greatly increased the abundance of birds. The highest total numbers of invertebrates and birds were recorded on land revegetated with Nootka lupin. On average 31 birds km-2 were recorded on barren land, 337 on heathland and 627 in Nootka lupin. Bird species composition differed between the two revegetation methods. Restored heathland provided habitat for waders of internationally decreasing populations, whereas Nootka lupin stands harboured more common bird species. Golden Plover (Pluvialis apricaria) and Dunlin (Calidris alpina) were most common on restored heathland, while Snipe (Gallinago gallinago) and Meadow Pipit (Anthus pratensis) were most common in Nootka lupine. The abundance of birds was positively correlated with that of invertebrates. The abundance of different bird species differed by successional stage in each habitat. The study showed the generally positive effects of revegetation on animal biodiversity and also how different revegetation methods produce different trajectories of ecosystem development.Hnignun vistkerfa og dreifing ágengra tegunda ógna líffræðilegum fjölbreytileika á heimsvísu. Vistheimt og landgræðsla eru mikilvægar aðgerðir til að endurheimta töpuð vistkerfi. Hvergi í Norður-Evrópu hefur jarðvegseyðing og eyðimerkurmyndun verið hraðari en á Íslandi. Í þessari rannsókn voru könnuð áhrif mismunandi landgræðsluaðgerða á þéttleika og tegundasamsetningu fugla og á fjölda smádýra. Rannsóknirnar voru gerðar á 26 stöðum á landinu. Á hverjum stað voru borin saman; a) óuppgrætt svæði, b) endurheimt mólendi og c) land sem hafði verið grætt upp með alaskalúpínu (Lupinus nootkatensis). Á óuppgræddu landi var að meðaltali 31 fugl á km2, 337 á endurheimtu mólendi og 627 á landi sem hafði verið grætt upp með lúpínu. Þéttleiki fugla hafði jákvæða fylgni við fjölda smádýra. Tegundasamsetning fugla var ólík eftir uppgræðsluaðferðum. Í endurheimtu mólendi var mest um vaðfugla af tegundum sem er að hnigna á heimsvísu, en í lúpínu var meira um algengari tegundir. Heiðlóa og lóuþræll voru algengustu tegundirnar í endurheimtu mólendi, en hrossagaukur og þúfutittlingur í lúpínu. Þéttleiki sumra fuglategunda virtist vera háður framvindustigi landgræðslusvæða. Þessi rannsókn sýnir að landgræðsla eykur líffræðilega fjölbreytni dýrategunda, en mismunandi landgræðsluaðgerðir leiða til mismunandi þróunar vistkerfanna.Náttúrusjóður Pálma Jónssonar; KvískerjasjóðurPeer Reviewe

Áhrif hækkaðs jarðvegshita á myndun koldíoxíðs (CO2 ), metans (CH4 ), hláturgass (N2 O), nituroxíðs (NO) og nitraðrar sýru (HONO) í skógarjarðvegi á Suðurlandi.

Geothermal areas can be local sources of greenhouse gases, both directly from the geothermal system or because of soil warming effects on biological sources. In this study we repeated field measurements methane (CH4) and nitrous oxide (N2O) fluxes along the soil temperature (Ts) gradient in a Sitka spruce (Picea sitchensis) stand at the ForHot study site in southern Iceland, where geothermal soil warming had started eight years earlier. We complemented these results with in situ measurements of carbon dioxide (CO2) and topsoil sampled in the same plots to study the production rates of those gases at 20 °C in the laboratory, as well as nitric oxide (NO) and nitrous acid (HONO). We showed that the eight year long exposure to elevated Ts had changed the topsoil, including its microbial properties and the production potentials of these gases. However, the production rates of CO2, CH4 and N2O measured in laboratory conditions did not clearly follow the in situ fluxes. We discuss both adaptation of microbes and origin of greenhouse gases (depth patterns and microbial vs. geothermal sources) as possible reasons for these discrepancies.Jarðhitasvæði geta verið uppsprettur ýmissa gróðurhúsalofttegunda, annað hvort beint upp úr jarðhitakerfinu eða vegna áhrifa aukins jarðvegshita á ýmsa lífræna ferla. Í þessari rannsókn endurtókum við mælingar á flæði metans (CH4) og hláturgass (N2O) með auknum jarðvegshita (Ts) í foldu í sitkagreniskógi (Picea sitchensis) á ForHot rannsóknasvæðinu á Suðurlandi, þar sem jarðhitasvæði hafði færst undir átta árum áður. Við bættum einnig við mælingum á losun koldíoxíðs (CO2) í foldu og bárum - niðurstöðurnar saman við losun þessara sömu gastegunda og nituroxíðs (NO) og nitraðrar sýru (HONO) úr jarðvegskjörnum úr sömu reitum sem mældir voru við 20 °C á rannsóknastofu. Niðurstöðurnar sýndu að átta ára jarðvegshlýnun hafði bæði breytt efnasamsetningu og örveruflóru reitanna og þar með getu til að framleiða áðurnefndar lofttegundir. Hinsvegar breyttist framleiðslugeta CO2, CH4 og N2O við 20 °C ekki reglulega með auknum Ts í foldu. Við ræðum bæði aðlögun örvera að auknum hita og hvernig uppruni gróðurhúsalofttegunda (úr mismunandi dýpi í jarðvegi og hvort hann er líffræðilegur eða jarðfræðilegur) getur mögulega útskýrt þær niðurstöður sem við fengum.The project was funded by the Academy of Finland (no. 297735 and no. 132045). This work also contributes to the ForHot-Forest (Project No.163272-051 of the Icelandic Research Council), as well as to the Nordic CAR-ES project and the ClimMani COST Action (ES1308) and the International Program CryoCARB and COUP. The Kuopio Naturalists’ Society is thanked for a travel grant. Jaana Rissanen is thanked for assisting in the laboratory at the University of Eastern Finland. We also want to acknowledge the staff at the Reykir campus of the Agricultural University of Iceland for great logistic support.Peer Reviewe

Carbon sequestration and community composition of ectomycorrhizal fungi across a geothermal warming gradient in an Icelandic spruce forest

Part of special issue: Ecology of Mycorrhizas in the Anthropocene Edited by Petr Kohout, Jan JansaSoil warming (0–5.5 °C above controls) effects on ectomycorrhizal growth, carbon sequestration and community composition were examined in a Picea sitchensis forest spanning a geothermal gradient in Iceland. Fungal communities were assayed with sand-filled ingrowth meshbags incubated in the soil for 5 months. Meshbags amended with compost made from maize leaves (a C4 plant enriched in 13C) were incubated for 5 or 12 months and used to estimate C sequestration by the fungal community. Despite increases in tree growth, moderate warming only slightly reduced or had no effect on mycelial growth and had no effect on fungal carbon sequestration or overall ectomycorrhizal community composition. Warming was associated with increased abundance of ascomycetes, particularly pyronemataceous ectomycorrhizal fungi, and altered saprotrophic community composition. Increased nitrate availability and root turnover may explain the lack of a positive ectomycorrhizal growth response to increased tree growth and observed shifts in community composition with warming.Svenska Forskningsrådet Formas. This research was supported by a grant from the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (nr: 239-2013-1113 for H. Wallander).Peer Reviewe

Temperature responses in a subarctic springtail from two geothermally warmed habitats

Common-garden experiments with populations sampled along natural thermal gradients help to reveal local adaptation, disentangle environmental and genetic effects, and ultimately predict, by analogy, future biotic responses to climate change. In this regard, geothermal habitats are useful model systems as they exhibit dramatic changes in soil temperature. The springtail Protaphorura pseudovanderdrifti has apparently coped with such local geothermal warming in Iceland, as this species occurs along a more than half-century-old geothermal gradient in a grassland and persists along a newly emerged temperature gradient in a previously non-geothermal planted spruce forest. We measured thermal reaction norms for development and walking speed and acute cold shock tolerance of P. pseudovanderdrifti originating from the grassland and forest geothermal gradients. Temperature-dependent juvenile development showed little variation among subpopulations from the recently warmed forest, probably due to insufficient evolutionary time, but springtails from the warmed grassland plots had significantly steeper reaction norms than their counterparts from the corresponding unwarmed plot. In contrast, cold tolerance and locomotory activity showed no conclusive clinal pattern despite significant within-habitat variation. There appeared to be significant differences between habitats, as springtails from the forest had more temperature-sensitive developmental rate and locomotory activity, walked faster, and exhibited more variable cold tolerance than grassland springtails did. The planting of a forest, therefore, seems to have exerted a stronger effect on the thermal phenotype of P. pseudovanderdrifti than the emergence of a geothermal gradient. Thus, habitat properties may be no less important in shaping thermal reaction norms than the mean temperature. These local-scale findings suggest that, in addition to warming per se, global transformation of communities may drive the evolution of thermal phenotypes to an extent comparable with the effect of rising environmental temperature

Prolonged exposure does not increase soil microbial community compositional response to warming along geothermal gradients

Global change is expected to affect soil microbial communities through their responsiveness to temperature. It has been proposed that prolonged exposure to elevated temperatures may lead to progressively larger effects on soil microbial community composition. However, due to the relatively short-term nature of most warming experiments, this idea has been challenging to evaluate. The present study took the advantage of natural geothermal gradients (from +1°C to +19°C above ambient) in two subarctic grasslands to test the hypothesis that long-term exposure (>50 years) intensifies the effect of warming on microbial community composition compared to short-term exposure (5–7 years). Community profiles from amplicon sequencing of bacterial and fungal rRNA genes did not support this hypothesis: significant changes relative to ambient were observed only starting from the warming intensity of +9°C in the long term and +7°C/+3°C in the short term, for bacteria and fungi, respectively. Our results suggest that microbial communities in high-latitude grasslands will not undergo lasting shifts in community composition under the warming predicted for the coming 100 years (+2.2°C to +8.3°C).This work was supported by Research Foundation–Flanders (FWO) [1293114N to JTW, 12B0716N to SV, 11G1615N to NIWL], Icelandic Research Council [163272-051 to BDS], Climate Change Manipulation Experiments in Terrestrial Ecosystems (ClimMani) COST Action [ES1308], the European Research Council grant ERC-SyG-610028 IMBALANCE-P and the University of Antwerp: University Research Fund (BOF).Peer Reviewe

Coupled carbon and nitrogen losses in response to seven years of chronic warming in subarctic soils

Increasing temperatures may alter the stoichiometric demands of soil microbes and impair their capacity to stabilize carbon (C) and retain nitrogen (N), with critical consequences for the soil C and N storage at high latitude soils. Geothermally active areas in Iceland provided wide, continuous and stable gradients of soil temperatures to test this hypothesis. In order to characterize the stoichiometric demands of microbes from these subarctic soils, we incubated soils from ambient temperatures after the factorial addition of C, N and P substrates separately and in combination. In a second experiment, soils that had been exposed to different in situ warming intensities (+0, +0.5, +1.8, +3.4, +8.7, +15.9 °C above ambient) for seven years were incubated after the combined addition of C, N and P to evaluate the capacity of soil microbes to store and immobilize C and N at the different warming scenarios. The seven years of chronic soil warming triggered large and proportional soil C and N losses (4.1 ± 0.5% °C−1 of the stocks in unwarmed soils) from the upper 10 cm of soil, with a predominant depletion of the physically accessible organic substrates that were weakly sorbed in soil minerals up to 8.7 °C warming. Soil microbes met the increasing respiratory demands under conditions of low C accessibility at the expenses of a reduction of the standing biomass in warmer soils. This together with the strict microbial C:N stoichiometric demands also constrained their capacity of N retention, and increased the vulnerability of soil to N losses. Our findings suggest a strong control of microbial physiology and C:N stoichiometric needs on the retention of soil N and on the resilience of soil C stocks from high-latitudes to warming, particularly during periods of vegetation dormancy and low C inputs

Responses of soil hexapod communities to increasing nitrogen in a subarctic grassland

Altres ajuts: acords transformatius de la UABThe warming of boreal ecosystems accelerates decomposition and increases nitrogen (N) availability. The impact of increased N on subarctic soil fauna communities, however, remains poorly understood. We investigated the response of soil hexapods to a N addition experiment in a subarctic grassland. We characterized the soil hexapod communities using environmental DNA metabarcoding and analyzed the levels of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial carbon (Cmic), and microbial nitrogen (Nmic). N addition increased DON and Nmic, while DOC and Cmic pools remained unchanged. Furthermore, N addition caused shifts in soil hexapod community compositional diversity between control and N plots in herbivore and microbivore taxa. The levels of DON and Nmic strongly correlated with these shifts, explaining 54% and 45% of the compositional variability, respectively. This study demonstrates a clear link between N availability and shifts in soil hexapod communities, associated to changes in microbial and dissolved N pools in subarctic grasslands

Responses of soil hexapod communities to warming are mediated by microbial carbon and nitrogen in a subarctic grassland

Altres ajuts: acords transformatius de la UABWarming in subarctic ecosystems will be two-fold higher compared to lower latitudes under current climate change projections. While the effects of warming in northern ecosystems on plants and microorganisms have been extensively studied, the responses of soil fauna have received much less attention, despite their important role in regulating key soil processes. We analyzed the response of soil hexapod communities in a subarctic grassland exposed to a natural geothermal gradient in Iceland with increases of +3 and + 6 °C above ambient temperature. We characterized hexapod communities using environmental DNA (eDNA) metabarcoding. We analyzed the amounts of microbial carbon (Cmic), microbial N (Nmic), dissolved organic C (DOC) and dissolved organic N (DON) and then assessed whether these variables could help to account for the compositional dissimilarity of ground hexapod communities across temperatures. The increases in soil temperature did lead to changes in the composition of hexapod communities. The compositional differences caused by +6 °C plots were correlated with a decrease in Cmic and Nmic, soil DOC and DON. Our results highlight the response of soil hexapods to warming, and their interaction with microbial biomass ultimately correlated with changes in the availabilities of soil C and N