Sirvi Autor "Sepp, Siim-Kaarel" järgi

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Arbuskulaarse mükoriisa roll taimede stressitaluvuses
(Tartu Ülikool, 2020) Sui, Simone; Öpik, Maarja; Sepp, Siim-Kaarel; Tartu Ülikool. Loodus- ja täppisteaduste valdkond; Tartu Ülikool. Botaanika osakond
Enamik maismaataimi on arbuskulaarmükoriissed. Arbuskulaarne mükoriisa on sümbioos taimejuure ja krohmseente (Glomeromycotina) vahel ning omab üliolulist rolli taimede toitainete kättesaadavuses ja omastamises. Lisaks on arbuskulaarsel mükoriisal teisigi tähtsaid funktsioone, näiteks taimede stressivastuste kujunemisel. Bakalaureusetöö eesmärk on anda ülevaade arbuskulaarse mükoriisa tähtsusest ökosüsteemides ja taimede biootilise ja abiootilise stressitaluvuses.
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Maakasutuse mõju arbuskulaarmükoriissete (AM) seente mitmekesisusele
(Tartu Ülikool, 2015) Sepp, Siim-Kaarel; Öpik, Maarja, juhendaja; Tartu Ülikool. Botaanika osakond; Tartu Ülikool. Loodus- ja tehnoloogiateaduskond
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Maakasutuse mõju arbuskulaarmükoriissete seente mitmekesisusele
(Tartu Ülikool, 2013) Sepp, Siim-Kaarel; Öpik, Maarja, juhendaja; Tartu Ülikool. Loodus- ja tehnoloogiateaduskond; Tartu Ülikool. Botaanika osakond
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Phenotypic plasticity masks evolutionary change in grasslandplant traits in response to land use abandonment
(2026-01) Tõnisson, Anastasia; Eck, Jenalle; Jing, Yuying; Kängsep, Piia; Laaspere, Lauri; Wu, Jianlu; Puura, Laura; Torsus, Mari; Koorem, Kadri; Moora, Mari; Sepp, Siim-Kaarel; Davison, John; Semchenko, Marina
Traditionally managed grasslands are among the most biodiverse habitats in Europe, but are threatened by land use abandonment. While the negative impacts of grazing and mowing cessation on species richness are well documented, little is known about potential evolutionary changes within species. Yet, intraspecific functional diversity is critical for successful grassland restoration and ensuring adaptive potential to future climate change. To disentangle the heritable and non-heritable components of population-level response to land use change in semi-natural grasslands, we examined 22 populations of a common grass, Briza media, from grazed sites and sites where grazing was abandoned, with resulting tree and shrub encroachment. We measured a range of traits under field conditions and following clonal propagation under common garden conditions. Field surveys revealed that abandonment resulted in litter accumulation, greater shading by woody and herbaceous vegetation, and lower temperature and moisture fluctuations compared with grazed sites. Plants responded to conditions at abandoned sites with phenotypic plasticity in traits that enhanced competitive ability for light (greater height and specific leaf area) but reduced tissue protection against stress (lower dry matter content). However, when the same genotypes were measured after clonal propagation in common conditions, counter-gradient variation was apparent, with heritable shifts towards increased tissue protection in populations from abandoned sites. When measured under field conditions, trait diversity was higher in sites with higher levels of shading and productive sites with higher variation in light conditions. However, high heritable trait diversity was instead characteristic of grazed sites with high densities of flowering B. media individuals. Synthesis. These findings demonstrate that land use change can cause evolutionary shifts and changes in heritable trait diversity that are masked in the field by phenotypic plasticity. Hence, the assessment of functional trait variation based on field observations is not a reliable way to assess the genetic variation essential for population adaptive potential.
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Plant mycorrhizal status indicates partner selectivity in arbuscular mycorrhizal interaction networks
(2024) Koorem, Kadri; Sepp, Siim-Kaarel; Bueno, C. Guillermo; Davison, John; Liu, Siqiao; Meng, Yiming; Semchenko, Marina; Vasar, Martti; Zobel, Martin; Moora, Mari
Mycorrhizal symbiosis, specifically arbuscular mycorrhiza, is one of Earth's oldest and most widespread symbiosis. Existing evidence suggests that plant species differ in their associations with mycorrhizal partners, with different species reported to be always (obligately mycorrhizal, OM), sometimes (facultatively mycorrhizal, FM) or never (non-mycorrhizal, NM) associating with arbuscular mycorrhizal (AM) fungi and this plant reliance on AM fungi is called plant mycorrhizal status. However, very little is known about how host plant mycorrhizal status shapes the network topology of interacting AM fungi. Here, we use a standardized sampling scheme to test whether plant species with different mycorrhizal statuses differ in mean AM fungal hyphal colonization and various indices of the AM fungal networks such as nestedness rank and resource range. We collected the roots and rhizosphere soil of 19 plant species representing five families. Each plant species was sampled from three distinct habitats. We determined AM fungal colonization in the roots and AM fungal community composition in roots and rhizosphere soil using molecular methods. We found that previously reported NM plant species had lower mean AM fungal colonization than FM plant species, but no differences were found between FM and OM plant species. Network analyses indicated that AM fungal communities in the roots of FM plant species had higher nestedness rank and resource range than networks associated with OM plant species, suggesting that OM plant species are more generalist regarding partner selection and interact with a wider range of fungal partners. Our results suggest that plant mycorrhizal status conveys useful information about the characteristics of AM fungal interaction networks, revealing that plant species consistently associated with AM fungi are less selective towards their fungal partners.
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Soil eukaryotic community responses to land use and host identity
(2020-10-30) Sepp, Siim-Kaarel; Öpik, Maarja, juhendaja; Zobel, Martin, juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
Mullaelustiku uurimine pole lihtne – lisaks sellele, et maa-alune elu jääb inimese igapäevasest tajuruumist kõrvale, on enamik mullas elutsevaid organisme kas mikroskoopilised või vähemalt piisavalt pisikesed, et nende leidmine, rääkimata liikide eristamisest, on keeruline. Õnneks tulevad siinkohal ökoloogidele appi DNA-põhised määramismeetodid. Selle tulemusena on tormiliselt arenema hakanud ökoloogiasuund, kus samaaegselt endisaegsete loodusuurijate tööga – kes kus elab? – uuritakse maapealsel elul põhinevate teooriate paikapidavust ka maa all. Doktoritöö käigus uurisin, kuidas mõjutab inimtegevus ühe olulise maa-aluse elustikurühma – peaaegu 80% maismaa taimeliikidega sümbioosis elavate arbuskulaarmükoriissete (AM) seente – elurikkust nii globaalsel skaalal ning Eestile omastes poollooduslikes kasvukohtades. Leidsin, et inimtegevusest (või selle tegevuse lõpetamisest) tingitud stress mõjutab suuresti koosluste koosseisu, kuid ei pruugi tingimata päädida vaadeldavate organismide liigirikkuse vähenemisega. Kuna liigilist koosseisu võib teatud lähenduses käsitleda koosluse funktsiooni indikaatorina, leidsin, et inimtegevuse mõju hindamiseks ei piisa pelgalt liikide loendamisest. Samuti leidsin, et looduslike ökosüsteemide AM seente liigirikkusele on inimtekkelistel häiringutel vastassuunaline mõju – vaesemates kasvukohtades elurikkust suurendav ning rikkamates vähendav. Puisniidul erinevaid organismirühmi uurides selgus, et inimtegevuse tõttu muutunud kasvukohtades muutuvad samaaegselt ja -suunaliselt mitmed päristuumsed organismirühmad, nii mükoriisaseened kui ka mullas elavad loomad. Lisaks leidsin vastupidiselt ootustele, et vaatamata enamiku taimeliikidega koos elavate AM seente väiksele globaalsele liigirikkusele (maismaa taimeliikide ning AM seeneliikide arvu suhe on umbes 300:1) ei ole taimejuurtesse „komplekteeritud“ AM seeneliikide kogum juhuslik, vaid mükoriisavõrgustikus eelistavad teatud peremeestaimed kindlaid seeneliike (või vastupidi).
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The Bug-Network (BugNet): A Global Experimental Network Testing the Effects of Invertebrate Herbivores and Fungal Pathogens on Plant Communities and Ecosystem Function in Open Ecosystems
(2025-10) Kempel, Anne; Adamidis, George C.; Anadón, José D.; Atkinson, Joe; Auge, Harald; Avtzis, Dimitrios; Bachelot, Benedicte; Bashirzadeh, Maral; Bota, Julien L.; Classen, Aimee; Constantinou, Ioannis; Crawley, Mick; de Bellis, Tonia; Dostal, Petr; Ebeling, Anne; Eisenhauer, Nico; Eldridge, David J.; Encina, Gustavo; Estrada, Catalina; Everingham, Susan; Fanin, Nicolas; Feng, Yanhao; Gaspar, Mario; Gooriah, Leana; Graff, Pamela; Gusmán Montalván, Elizabeth; Gusmán Montalván, Pamela; Hartke, Tamara R.; Huang, Linjia; Jochum, Malte; Kaljund, Karin; Karmiris, Ilias; Koorem, Kadri; Korell, Lotte; Laine, Anna-Liisa; le Provost, Gaëtane; Lessard, Jean-Philippe; Liu, Mu; Liu, Xiang; Liu, Yanjie; Llancabure, Juan; Loïez, Sidonie; Loydi, Alejandro; Marrero, Hugo; Gockel (McMahan), Shelby; Montoya, Adrián; Münzbergová, Zuzana; Niu, Yujie; Ott, David; Oyarzabal, Mariano; Panitsa, Maria; Papatheodorou, Effimia; Piper, Frida I.; Püssa, Kersti; Rand, Karin; Saiz, Hugo; Sanders, Nathan J.; Schädler, Martin; Scherber, Christoph; Semchenko, Marina; Sepp, Siim-Kaarel; Shah, Manzoor Ahmad; Shaheen, Ishrat; Stein, Claudia; Stewart, Jana; Tang, Zhuangsheng; Tschan, Georg; van Nouhuys, Saskya; Vandegehuchte, Martijn L.; Vernon, Millie; V. R., Sonali; Wang, Jianyong; Xiao, Yao; Xystrakis, Fotios; Yang, Jie; Yang, Siwei; Zografou, Konstantina; Allan, Eric
Plants are consumed by a variety of organisms, including herbivores and pathogens, which significantly impact plant biomass, diversity, community composition, and ecosystem functioning. While the impacts of vertebrate herbivores are well established, the effects of consumer groups such as insect herbivores, mollusks, and fungal pathogens on plant communities are less clear and remain understudied in many systems. Existing evidence of how they affect plant biomass, diversity, and community composition is mixed, and most studies have focused on individual consumer groups in isolation. However, different consumer groups interact with each other, directly or indirectly, in ways that alter their impacts on plants, and the consequences of these interactions for plant community structure and ecosystem function remain understudied. Further, consumer impacts vary across environmental gradients and likely depend on abiotic conditions such as climate, soil type, or elevation, and biotic conditions such as plant productivity, diversity, or community composition. Existing studies testing the impacts of invertebrate herbivores and fungal pathogens on plant communities differ substantially in methodology, making generalities across large scales difficult. This calls for experimental approaches that implement standardized protocols across many sites. Here, we introduce and report on the methodology of a novel global research network, The Bug-Network (BugNet), that implements standardized consumer-reduction experiments across 5 continents and 18 countries in diverse, herbaceous- or shrub-dominated ecosystems to investigate: (1) the influence of fungal pathogens, insect herbivores, and mollusks on plant diversity and ecosystem functioning, (2) interactions among these consumer groups, and (3) the abiotic and biotic drivers of context-dependent consumer impacts. BugNet aims to advance a predictive understanding of plant-consumer interactions in order to test fundamental ecological hypotheses and improve predictions of global change impacts on biodiversity and ecosystem functioning.