A review of open top chamber (OTC) performance across the ITEX Network

Open top chambers (OTCs) were adopted as the recommended warming mechanism by the International Tundra Experiment (ITEX) network in the early 1990’s. Since then, OTCs have been deployed across the globe. Hundreds of papers have reported the impacts of OTCs on the abiotic environment and the biota. Here we review the impacts of the OTC on the physical environment, with comments on the appropriateness of using OTCs to characterize the response of biota to warming. The purpose of this review is to guide readers to previously published work and to provide recommendations for continued use of OTCs to understand the implications of warming on low stature ecosystems. In short, the OTC is a useful tool to experimentally manipulate temperature, however the characteristics and magnitude of warming varies greatly in different environments, therefore it is important to document chamber performance to maximize the interpretation of biotic response. When coupled with long-term monitoring, warming experiments are a valuable means to understand the impacts of climate change on natural ecosystems

Microbes, mosses and lichens

Climate warming in sub-Arctic regions leads to shifts in plant communities and retreating glaciers. Mosses and lichens contribute to important ecosystem processes in these environments, including nitrogen fixation via their microbiome. The first objective of this dissertation was to understand the extent to which long-term warming affects bacterial communities associated with the lichen Cetraria islandica. In the same context, the bacterial community and nitrogen fixation rates associated with the moss Racomitrium lanuginosum were investigated. These species are among the most common lichen and moss species in Iceland, respectively. Paper I shows that long-term warming affects the structure and composition of the bacterial community associated with C. islandica and that this change is partly mediated via changes in the plant community. The same is true for the bacterial communities associated with R. lanuginosum, although nitrogen fixation rates are apparently not affected by warming, potentially due to warming-induced shifts in nitrogen-fixing taxa (Paper II). The second objective was to evaluate the extent to which bacterial communities of two common Racomitrium species and the underlying soil as well as the moss-associated nitrogen fixation change during primary succession and whether these changes are related to changes in moss functional traits. The bacterial community composition associated with Racomitrium mosses was correlated with the successional stage in the Fláajökull forefield, and also with moss moisture content. The bacterial communities of the underlying soil also shifted with succession and were in addition related to the moss C:N ratio. Nitrogen fixation rates did not change with time since deglaciation, but were correlated with the bacterial community structure.Meðal afleiðinga hlýnunar loftslags á norðurslóðum má nefna hörfun jökla og ýmsar gróðurbreytingar. Mosar og fléttur leggja mikið af mörkum til vistkerfislegra ferla í hinu kalda umhverfi norðurslóða, þar á meðal bindingu köfnunarefnis með aðstoð þeirra örvera sem í þeim þrífast. Eitt af meginmarkmiðum þeirra rannsókna sem greint er frá í ritsmíð þessari er að leiða fram að hve miklu leyti loftslagshlýnun á áratuga skala hefur áhrif á örverusamfélög í fléttunni Cetraria islandica (fjallagrös) og í gamburmosanum Racomitrium lanuginosum (hraungambri). Þessar tegundir eru meðal algengustu fléttu- og mosategunda í mörgum íslenskum vistgerðum. Í Grein I er sýnt fram á að langtímahlýnun hefur áhrif á samsetningu örverulífríkisins í fjallagrösum og að þau áhrif eru að hluta tengd breytingum á aðlægum gróðri. Hið sama reyndist eiga við um örverusamfélög hraungambra, nema hvað, að hlýnunin reyndist ekki hafa marktæk áhrif á niturbindingu, og kom fram að sú niðurstaða gæti skýrst af breyttri tegundasamsetningu niturbindandi baktería (Grein II). Annað meginmarkmið rannsóknanna var að meta að hve miklu leyti örverusamfélög í tveimur gamburmosategundum og í jarðveginum sem þær vaxa á taka breytingum með gróðurframvindu og hvort þær breytingar tengjast ástandi mosans og starfsemi á borð við niturbindingu. Örverusamfélögin voru þannig kortlögð með tilliti til aldurs jökulgarða Fláajökuls, og einnig við rakainnihald mosans. Bakteríusamfélög í jarðveginum tóku skýrum breytingum með aldri jökulgarðanna, og stóðu einnig í samhengi við C:N hlutfall mosans sem á honum óx. Niturbinding stóð ekki í marktæku samhengi við aldur jökulgarðanna, en var hins vegar skýrt fylgin samsetningu örverulífríkisins

Draft Metagenome Sequences of the Sphagnum (Peat Moss) Microbiome from Ambient and Warmed Environments across Europe

We present 49 metagenome assemblies of the microbiome associated with Sphagnum (peat moss) collected from ambient, artificially warmed, and geothermally warmed conditions across Europe. These data will enable further research regarding the impact of climate change on plant-microbe symbiosis, ecology, and ecosystem functioning of northern peatland ecosystems

Moss and underlying soil bacterial community structures are linked to moss functional traits

Mosses are among the first colonizing organisms after glacier retreat and can develop into thick moss mats during later successional stages. They are key players in N2 fixation through their microbiome, which is an important process for nutrient buildup during primary succession. How these moss–microbe interactions develop during succession is not well studied and is relevant in the light of climate change and increased glacier retreat. We examined how the bacterial communities associated with two moss species of the genus Racomitrium and the underlying soil, as well as moss traits and nitrogen fixation, develop along a successional gradient in the glacier forefield of Fláajökull in southeast Iceland. In addition, we tested whether moss functional traits, such as total carbon (TC) and total nitrogen (TN) contents, moss moisture content, and moss shoot length are drivers of moss and underlying soil bacterial communities. Although time since deglaciation did not affect TN and moss moisture contents, TC and shoot length increased with time since deglaciation. Moss and underlying soil bacterial communities were distinct. While the soil bacterial community structure was driven by moss C/N ratios, the moss bacterial community structure was linked to time since deglaciation, moss C/N ratio, and moss moisture content. Moss N2-fixation rates were linked to bacterial community composition and nifH gene abundance rather than moss TN or time since deglaciation. This was accompanied by a shift from autotrophic to heterotrophic diazotrophs. Overall, our results suggest that there is little lateral transfer between moss and soil bacterial communities and that moss traits affect moss and soil bacterial community structure. Only moss bacterial community changed with time since deglaciation. In addition, moss N2-fixation rates are determined by bacterial community structure, rather than moss traits or time since deglaciation. This study on the interplay between succession, mosses, soils, and their bacterial communities will inform future work on the fate of newly exposed areas as a result of glacier retreat.Peer reviewe

Draft Metagenome Sequences of the Sphagnum (Peat Moss) Microbiome from Ambient and Warmed Environments across Europe

We present 49 metagenome assemblies of the microbiome associated with Sphagnum (peat moss) collected from ambient, artificially warmed, and geothermally warmed conditions across Europe. These data will enable further research regarding the impact of climate change on plant-microbe symbiosis, ecology, and ecosystem functioning of northern peatland ecosystems

Draft Metagenome Sequences of the Sphagnum (Peat Moss) Microbiome from Ambient and Warmed Environments across Europe.

We present 49 metagenome assemblies of the microbiome associated with Sphagnum (peat moss) collected from ambient, artificially warmed, and geothermally warmed conditions across Europe. These data will enable further research regarding the impact of climate change on plant-microbe symbiosis, ecology, and ecosystem functioning of northern peatland ecosystems

Draft Metagenome Sequences of the Sphagnum (Peat Moss) Microbiome from Ambient and Warmed Environments across Europe.

We present 49 metagenome assemblies of the microbiome associated with Sphagnum (peat moss) collected from ambient, artificially warmed, and geothermally warmed conditions across Europe. These data will enable further research regarding the impact of climate change on plant-microbe symbiosis, ecology, and ecosystem functioning of northern peatland ecosystems