Yliopiston etusivulle Suomeksi På svenska In English Helsingin yliopisto

Archaea in the Mycorrhizosphere of Boreal Forest Trees

Show full item record

Files in this item

Files Description Size Format View/Open
archaeai.pdf 857.8Kb PDF View/Open
Use this URL to link or cite this item: http://urn.fi/URN:ISBN:978-952-10-4726-8
Vie RefWorksiin
Title: Archaea in the Mycorrhizosphere of Boreal Forest Trees
Author: Bomberg, Malin
Contributor: University of Helsinki, Department of Applied BiologyUniversity of Helsinki, Faculty of Biosciences, Department of Biological and Environmental Sciences, Microbiology
Thesis level: Doctoral dissertation (article-based)
Abstract: Archaea were long thought to be a group of ancient bacteria, which mainly lived in extreme environments. Due to the development of DNA sequencing methods and molecular phylogenetic analyses, it was shown that the living organisms are in fact divided into three domains; the Archaea, Bacteria and the Eucarya. Since the beginning of the previous decade, it was shown that archaea generally inhabit moderate environments and that these non-extremophilic archaea are more ubiquitous than the extremophiles. Group 1 of non-extreme archaea affiliate with the phylum Crenarchaeota. The most commonly found soil archaea belong to the subgroup 1.1b. However, the Crenarchaeota found in the Fennoscandian boreal forest soil belong to the subgroup 1.1c. The organic top layer of the boreal forest soil, the humus, is dominated by ectomycorrhizal fungal hyphae. These colonise virtually all tree fine root tips in the humus layer and have been shown to harbour distinct bacterial populations different from those in the humus. The archaea have also been shown to colonise both boreal forest humus and the rhizospheres of plants. In this work, studies on the archaeal communities in the ectomycorrhizospheres of boreal forest trees were conducted in microcosms. Archaea belonging to the group 1.1c Crenarchaeota and Euryarchaeota of the genera Halobacterium and Methanolobus were detected. The archaea generally colonised fungal habitats, such as ectomycorrhizas and external mycelia, rather than the non-mycorrhizal fine roots of trees. The species of ectomycorrhizal fungus had a great impact on the archaeal community composition. A stable euryarchaeotal community was detected especially in the mycorrhizas, of most of the tested Scots pine colonising ectomycorrhizal fungi. The Crenarchaeota appeared more sporadically in these habitats, but had a greater diversity than the Euryarchaeota. P. involutus mycorrhizas had a higher diversity of 1.1c Crenarchaeota than the other ectomycorrhizal fungi. The detection level of archaea in the roots of boreal trees was generally low although archaea have been shown to associate with roots of different plants. However, alder showed a high diversity of 1.1c Crenarchaeota, exceeding that of any of the tested mycorrhizas. The archaeal 16S rRNA genes detected from the non-mycorrhizal roots were different from those of the P. involutus mycorrhizas. In the phylogenetic analyses, the archaeal 16S rRNA gene sequences obtained from non-mycorrhizal fine roots fell in a separate cluster within the group 1.1c Crenarchaeota than those from the mycorrhizas. When the roots of the differrent tree species were colonised by P. involutus, the diversity and frequency of the archaeal populations of the different tree species were more similar to each other. Both Cren- and Euryarchaeota were enriched in cultures to which C-1 substrates were added. The 1.1c Crenarchaeota grew anaerobically in mineral medium with CH4 and CO2 as the only available C sources, and in yeast extract media with CO2 and CH4 or H2. The crenarchaeotal diversity was higher in aerobic cultures on mineral medium with CH4 or CH3OH than in the anaerobic cultures. Ecological functions of the mycorrhizal 1.1c Crenarchaeota in both anaerobic and aerobic cycling of C-1 compounds were indicated. The phylogenetic analyses did not divide the detected Crenarchaeota into anaerobic and aerobic groups. This may suggest that the mycorrhizospheric crenarchaeotal communities consist of closely related groups of anaerobic and aerobic 1.1c Crenarchaeota, or the 1.1c Crenarchaeota may be facultatively anaerobic. Halobacteria were enriched in non-saline anaerobic yeast extract medium cultures in which CH4 was either added or produced, but were not detected in the aerobic cultures. They may potentially be involved in anaerobic CH4 cycling in ectomycorrhizas. The CH4 production of the mycorrhizal samples was over 10 times higher than for humus devoid of mycorrhizal hyphae, indicating a high CH4 production potential of the mycorrhizal metanogenic community. Autofluorescent methanogenic archaea were detected by microscopy and 16S rRNA gene sequences of the genus Methanolobus were obtained. The archaeal community depended on both tree species and the type of ectomycorrhizal fungus colonising the roots and the Cren- and Euryarchaeota may have different ecological functions in the different parts of the boreal forest tree rhizosphere and mycorrhizosphere. By employing the results of this study, it may be possible to isolate both 1.1c Crenarchaeota as well as non-halophilic halobacteria and aerotolerant methanogens from mycorrhizospheres. These archaea may be used as indicators for change in the boreal forest soil ecosystem due to different factors, such as exploitations of forests and the rise in global temperature. More information about the microbial populations with apparently low cell numbers but significant ecological impacts, such as the boreal forest soil methanogens, may be of crucial importance to counteract human impacts on such globally important ecosystems as the boreal forests.Arkéer i skogsträdens svamprötter

Arkéerna antogs länge vara en uråldrig typ av bakterier som bebodde endast extrema miljöer (t.ex. heta källor, sjöar med hög salt halt). Med hjälp av DNA baserade metoder påvisades det dock att arkéerna tillhörde en helt egen grupp av organismer och att livsformerna på jorden kan indelas i tre domäner, nämnligen Archaea, Bacteria och Eucaryota. Sedan början av 1990-talet har man förutom i olika vatten och jord prov, funnit att arkéerna är allmänt spridda i olika vanliga miljöer och att de typer som typiskt hittas i finsk skogsjord skiljer sej åtskilligt från de arkéer som vanligen hittas i jord.

I det organiska ytskiktet, humusen, i de boreala skogarna växer stora mänger svamphyfer. Dessa bildar symbiotiska förhållanden med skogsträdens rötter, så kallade mykorrhizor. Dessa har påvisats ha speciella bakteriefloror som skiljer sej från den i humusen. Också arkéer har påvisats leva både i skogshumus samt på växtrötter.

I den här forskningen studerades arké-populationerna i boreala skogsträds ektomykorrhizosfär. Man fann att mykorrhizorna och svamphyferna i allmänhet har en större population av arkéer än de 'nakna' trädrötterna eller humus utan svamphyfer. Både svamparterna och trädarterna inverkar på bestånder av arkéer i rötterna och mykorrhizosfären. Mykorrhizornas arkéer skiljer sej från dem som hittas på rötterna, men rötternas bestånd av arkéer förändras då mykorrhizosfären i rötterna bildas. Förutom de crenarkeoter som vanligen hittas i finsk skogsjord hittades i de flesta mykorrhiza-prov också sekvenser av gener för ribosomalt RNA som tillhörde släktet Halobacterium, vilka i allmänhet lever i väldigt hög salthalt. Arkéer hittades också i både anaeroba och aeroba oldingar. I de anaeroba metan-producerande odlingarna hittades euryarkeoter av släktena Methanolobus (methan-producerande arkéer) och Halobacterium samt de crenarkeoter som typiskt hittas i finsk skogsjord. I de aeroba odlingarna matade med antingen metan eller formamid (en komponent av metancykeln) hittades bara crenarkeoter.

Inga ekologiska funktioner har ännu påvisats för de arkéer som hittats i finsk skogsjord och i trädenas rötter och mykorrhizosfär, men dessa resultat indikerar att de kan ha en betydelse för metanets kretslop i både anaeroba och aeroba förhållanden. Man har ännu inte lyckats isolera dessa arkéer för att kunna studera deras fysiologi, men genom att tillämpa dessa reultat kan detta vara möjligt. Genom att få mera information om de här dåligt kända mikro-organismerna kunde de möjligen också få en användning som indikatororganismer för att registrera förändringar i skogsjordens ekosystem, förorsakade av olika faktorer, såsom intensivt skogsbruk men också den globala temperaturökningen. Mera information om viktiga mikrobgrupper med troligtvis låg populationstäthet men stor ekologisk betydelse, som t.ex. metanogenerna i skogsjorden, kan vara av stor betydelse för att kunna minska de miljöeffekter människan förorsakar dessa globalt viktiga ekosystem.
URI: URN:ISBN:978-952-10-4726-8
http://hdl.handle.net/10138/22073
Date: 2008-06-11
Copyright information: This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
This item appears in the following Collection(s)

Show full item record

Search Helda


Advanced Search

Browse

My Account