Ecology of ericoid mycorrhizal fungi
Date
2018-09-25
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Abstract
Sümbioos mükoriisa ehk seenjuure vahendusel on üks vanimaid ja enim levinud mutualismivorme maailmas. Mükoriissetes suhetes seenpartner varustab taime vees lahustunud mineraalainetega ning saab taimelt vastu suhkruid. Erikoidne mükoriisa (ErM) on arbuskulaarse mükoriisa ja ektomükoriisa kõrval evolutsiooniliselt noorim mükoriisatüüp. Taimed sugukonnast kanarbikulised (Ericaceae), kuhu kuuluvad ka mustikas, pohl ja kanarbik, moodustavad ErM sümbioosi mitmete rühmade mullas ja juurtes elavate endofüütsete seentega. Seenehüüfid kasvavad taime juurerakkudesse sisse ja moodustavad paunakesi – ajukujulisi struktuure, kus taime rakumembraani ja seeneraku piirpind on oluliselt suurenenud toitaainete vahetuse soodustamiseks. Kanarbikulised esinevad sageli vaestel happelistel muldadel, kus toitained on peamiselt orgaanilisel kujul ja raskesti taimedele omastatavad. Kanarbikuliste peamine ökoloogiline kohastumus ongi mükoriisaseente abil makro- ja mikroelementide kättesaamine. Kanarbikulised on metsanduse ja põllumajanduse aspektist väheolulised, mistõttu ErM ökofüsioloogia ja sellega seotud seente elurikkust on vähe uuritud võrreldes teiste mükoriisatüüpidega. Senised elurikkuse uuringud ja mükoriisa sünteesi katse näitavad, et ErM moodustavad seened kuuluvad mitmesse kottseente (Helotiales, Chaetothyriales) ja kandseente (Sebacinales, Hymenochaetales) seltsidesse. Oma väitekirjas keskendun erinevatele aspektidele ErM seente elurikkuses ja ökoloogias, eelkõige keskkonnaparameetritele, mis mõjutavad seenekooslusi. ErM seente tuvastamiseks isoleerisin kanarbikuliste ja hariliku kuuse juurtes kasvavad seened puhaskultuuri Tsehhimaa ja Norra metsadest ning viisin läbi mükoriisa sünteesi katsed laboris. Välitööde käigus kogusime kanarbikuliste juuri Mount Wilhelmi mäelt Paapua Uus-Guineas ja Drakensbergi mägedest Lõuna-Aafrika Vabariigis. Kasutasin Roche 454 pürosekveneerimise tehnoloogiat sealt kogutud juurtelt seente määramiseks. Leidsin, et senimääramata kandseente haru moodustab erikoidset mükoriisat, kus taimerakkude pinnal areneb õhuke seeneniidistiku kiht ja seen soodustab mustika kasvu ning lagundab aromaatseid polümeere. Kuusejuurtelt isoleeritud kottseened Pezoloma ericae liigikompleksist on võimelised moodustama erikoidsele mükoriisale iseloomulikke struktuure mustika juurerakkudes. Kottseeneliik Acephala macrosclerotiorum moodustab ektomükoriisat hariliku kuusega ja erikoidset mükoriisat mustikaga laboritingimustes. Kanarbikuliste seenekooslusi mõjutavad paljud keskkonnaparameetrid, eelkõige kõrgus üle merepinna, peremeestaime liik ning mikroelupaik niiskuse gradiendil. Erikoidset mükoriisat moodustavad seened erinevad tugevasti oma leviku poolest.
Vast majority of plants live in mutually beneficial partnership with soil fungi. This partnership is called mycorrhizal symbiosis, which plays a crucial role in plant nutrient uptake. Plants feed symbiotic fungi with energy-rich compounds, such as sugars. Mycorrhizal symbiosis is one of the oldest and the most widespread symbioses on the Earth. Several types of mycorrhizal symbiosis have evolved during almost 500 million years. One of the youngest mycorrhizal type is ericoid mycorrhizal (ErM) symbiosis, a mutualistic relationship formed between plants from the Ericaceae family (so-called ericoid mycorrhizal plants; e.g. blueberry, rhododendron, heather) and diverse group of soil fungi (so-called ericoid mycorrhizal fungi). Ericoid mycorrhizal plants often occur in very harsh environments on extremely poor soils, where most of the nutrients are not directly available for plants, because these are locked up in complex forms of soil organic matter. The ErM symbiosis represents a key evolutionary adaptation of ErM plants to take up the nutrients from such substrates and survive in unfavorable conditions. In spite of the importance of ErM for the plants and fungi as well as for functioning of the ecosystems, ErM remains largely overlooked compared to the more common mycorrhizal types, such as arbuscular mycorrhiza and ectomycorrhizal; and a broader general understanding of the ErM symbiosis is therefore lacking. In this thesis, I focus on Ericaceae-associated fungi from various aspects of the partnership. Firstly, this thesis aims to determine the occurrence of ericoid mycorrhizal life-style among fungi. Furthermore, the thesis also focused on determination of environmental factors which significantly affect composition of fungal communities associated with roots of ErM plants. I found a novel lineage of fungi from the Basidiomycota phylum, which formed characteristic sheathed ErM symbiosis and enhanced growth of blueberry in vitro. This mycobiont showed even better ability to degrade a highly recalcitrant substrate compare to previsouly determined ErM fungi. In addition, I found that the communities of Ericaceae root-associated fungi were affected by environmental factors such as elevation and host plant species on a local spatial scale. On the global scale I found that some ErM fungal species have a very broad distribution range, while other species have much narrower distribution range restricted to a single hemisphere or continent.
Vast majority of plants live in mutually beneficial partnership with soil fungi. This partnership is called mycorrhizal symbiosis, which plays a crucial role in plant nutrient uptake. Plants feed symbiotic fungi with energy-rich compounds, such as sugars. Mycorrhizal symbiosis is one of the oldest and the most widespread symbioses on the Earth. Several types of mycorrhizal symbiosis have evolved during almost 500 million years. One of the youngest mycorrhizal type is ericoid mycorrhizal (ErM) symbiosis, a mutualistic relationship formed between plants from the Ericaceae family (so-called ericoid mycorrhizal plants; e.g. blueberry, rhododendron, heather) and diverse group of soil fungi (so-called ericoid mycorrhizal fungi). Ericoid mycorrhizal plants often occur in very harsh environments on extremely poor soils, where most of the nutrients are not directly available for plants, because these are locked up in complex forms of soil organic matter. The ErM symbiosis represents a key evolutionary adaptation of ErM plants to take up the nutrients from such substrates and survive in unfavorable conditions. In spite of the importance of ErM for the plants and fungi as well as for functioning of the ecosystems, ErM remains largely overlooked compared to the more common mycorrhizal types, such as arbuscular mycorrhiza and ectomycorrhizal; and a broader general understanding of the ErM symbiosis is therefore lacking. In this thesis, I focus on Ericaceae-associated fungi from various aspects of the partnership. Firstly, this thesis aims to determine the occurrence of ericoid mycorrhizal life-style among fungi. Furthermore, the thesis also focused on determination of environmental factors which significantly affect composition of fungal communities associated with roots of ErM plants. I found a novel lineage of fungi from the Basidiomycota phylum, which formed characteristic sheathed ErM symbiosis and enhanced growth of blueberry in vitro. This mycobiont showed even better ability to degrade a highly recalcitrant substrate compare to previsouly determined ErM fungi. In addition, I found that the communities of Ericaceae root-associated fungi were affected by environmental factors such as elevation and host plant species on a local spatial scale. On the global scale I found that some ErM fungal species have a very broad distribution range, while other species have much narrower distribution range restricted to a single hemisphere or continent.
Description
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Keywords
mycorrhiza, symbiosis, Ericaceae, mycobiota, biological diversity, synecology