Sirvi Autor "Koorem, Kadri" järgi

Nüüd näidatakse 1 - 3 3

The influence of abiotic and biotic factors on small-scale plant community patterns and regeneration in boreonemoral forest
(2012-10-16) Koorem, Kadri
Taimed „tajuvad“ neid vahetult ümbritsevat keskkonda ja suudavad oma kasvu vastavalt sellele kohandada. Näiteks on teada, et taimed suudavad suunata oma juuri toitaineterikkasse laiku. Samuti sõltub taime kasv sümbiontsetest arbuskulaar- mükoriissetest (AM) seentest, mis aitavad neil mullast toitaineid omastada. Metsa alustaimestikus kasvavad taimed on oluliselt mõjutatud ka puittaimede poolt, mille varis ümbritsevat keskkonda suuresti kujundab. Hoolimata senisest teadmisest ei ole siiani selge, kuivõrd olulised on eelpool toodud faktorid alustaimestiku produktiivsuse, paljunemisedukuse ja liigilise koosseisu mõjutamisel. Nimetatud lünkade täitmiseks meie teadmistes valisin mudelsüsteemiks vana salukuusiku, mille põõsarindes domineerib harilik sarapuu ja alustaimestik on väga liigirikas. Tulemused näitasid, et väikesel skaalal mõjutab toitainetesisaldus ja AM seente ohtrus mullas rohttaimede maapealset biomassi. Leitud muster viitab sellele, et paranenud ressursside kättesaadavuse kasutavad taimed ära valguskonkurentsis edukamad olemiseks. Samas ei mõjutanud mulla toitainetesisaldus ega AM seente ohtrus taimede maa-alust biomassi. Suure toitainetesisalduse juures suudavad taimed neid edukalt mullast omastada ning toitainete madala kättesaadavuse korral suudavad nad „veenda“ AM seeni oma juuri asustama ning tõhusamalt toitaineid trantsportima. Sellise mehhanismi olemasolu näitas kaudselt ka salukuusikule iseloomuliku taimeliigi idandite parem kasv koos AM seentega olukorras, kus toitaineid mullas nappis. Laia ökoloogilise amplituudiga taimeliigi idandite kasv aga ei sõltunud oluliselt AM seente ohtrusest ei toitainetevaesel ega rikkal mullal. Lisaks näitasid tulemused, et metsa alustaimestiku taimeliikide idanemine ja idandite kasv sõltub oluliselt varisekihi paksusest ja tüübist— kuuse varis pärssis neid arenguetappe, samas kui sarapuu varis mõjus pigem soodustavalt. Varise mõju oli ilmne ka looduses — sarapuu all, kus oli kolm korda õhem varisekiht, leidus alustaimestikus poole rohkem liike kui kuuse all. Selle doktoritöö tulemused aitavad meil paremini mõista metsa alustaimestiku dünaaamikat. Suurenenud teadmiste hulka aitab säilitada metsadele iseloomulikku taimede liigirikkust kuna suure enamiku metsas kasvavatest taimeliikidest leiab alustaimestikust.
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.
Symbiont plasticity as a driver of plant success
(2024) Zobel, Martin; Koorem, Kadri; Moora, Mari; Semchenko, Marina; Davison, John
We discuss which plant species are likely to become winners, that is achieve the highest global abundance, in changing landscapes, and whether plant-associated microbes play a determining role. Reduction and fragmentation of natural habitats in historic landscapes have led to the emergence of patchy, hybrid landscapes, and novel landscapes where anthropogenic ecosystems prevail. In patchy landscapes, species with broad niches are favoured. Plasticity in the degree of association with symbiotic microbes may contribute to broader plant niches and optimization of symbiosis costs and benefits, by downregulating symbiosis when it is unnecessary and upregulating it when it is beneficial. Plasticity can also be expressed as the switch from one type of mutualism to another, for example from nutritive to defensive mutualism with increasing soil fertility and the associated increase in parasite load. Upon dispersal, wide mutualistic partner receptivity is another facet of symbiont plasticity that becomes beneficial, because plants are not limited by the availability of specialist partners when arriving at new locations. Thus, under conditions of global change, symbiont plasticity allows plants to optimize the activity of mutualistic relationships, potentially allowing them to become winners by maximizing geographic occupancy and local abundance.