Belowground plant diversity and coexistence patterns in grassland ecosystems
Date
2012-09-25
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Abstract
Teadmised taimekoosluste liigilisest mitmekesisusest ja liikide kooseksisteerimisest põhinevad uuringutele, mis käsitlevad koosluste maapealset osa. Kuigi paljudes parasvöötme niidukooslustes võib isegi kuni 75% taimsest biomassist olla paigutunud maa alla, ei ole sealsetest protsessidest kuigi palju teada, kuna varasemad meetodid ei võimaldanud välimuselt väga sarnaseid juuri ja risoome liikideks määrata. Taimede juuresüsteemid on väga laiaulatuslikud ja on ajas tunduvalt vastupidavamad kui maapealsed võsud, mistõttu võib maa all esineda samas ruumiskaalas rohkem liike kui maa peal. Doktoritöös uurisin, milliseid erinevusi võib leida maa-alustes ja maapealsetes mitmekesisuse mustrites ning täiendasin seniseid teadmisi taimekoosluse funktsioneerimisest ja taimede suhetest juurtes elavate mükoriisa seentega.
Kasutades uue põlvkonna sekveneerimist leidsin, et maa-alune taimede liigirikkus on kuni kaks korda suurem kui maa peal. Määrasin juurtest ka taimedega sümbioosis olevate seente, täpsemalt arbuskulaarmükoriisa liigid ning leidsime, et seente liigiline mitmekesisus ja fülogeneetiline mitmekesisus kasvab taimede liigilise ja fülogeneetilise mitmekesisuse kasvades. Taimede liigirikkus maa peal ja maa all erines ka piki mullaviljakuse gradienti. Leidsin sarnaselt varasemate töödega, et maapealne liigirikkus langeb mullaviljakuse kasvades, kuid uudne aspekt on, et maa-aluste liikide arv kasvas mullaviljakuse kasvades. Sarnaselt elurikkusele selgus ka, et maapealne ja maa-alune taimekooslus on kokku pandud erinevate protsesside tagajärjel: maapealsete liikide kooseksisteerimine on määratud biootiliste suhete poolt, nagu näiteks valguskonkurents, samas kui maa-aluse koosluse kokkupanekut mõjutavad suuresti abiootilised ja stohhastilised protsessid (erinevad toitainete gradiendid, mulla pH, jm). Antud tulemused viitavad sellele, et vaadeldes ainult koosluse maapealset osa, näeme kõigest "jäämäe tippu", kuna tegelik liikide kooseksisteerimine leiab aset maa all. Selle doktoritöö tulemused toovad esimest korda esile taimekoosluste maa-aluse komponendi olulisuse liikide kooseksisteerimise ja ökosüsteemi protsesside uurimisel.
Our current understanding about plant species diversity and coexistence is almost entirely based on studies of aboveground vegetation. In some species-rich grassland ecosystems, nearly 75% of plant biomass occurs belowground, however, little is known about below-ground processes due to difficulties in distinguishing between morphologically similar roots of different species. Belowground root systems are more extensive in space and more persistent in time than short-lived shoots, causing belowground species richness to be higher than aboveground per volume. In this thesis I explored the differences between the patterns of below-and aboveground plant diversity with adding new insights to the knowledge of mutualistic relationships between plants and root dwelling fungi and the functioning of plant communities as a whole. Application of next-generation sequencing revealed that belowground plant species richness can be up to twice as high as aboveground. By using the same root samples I identified arbuscular mycorrhizal fungi forming tight mutualistic relationships with plants and found that fungal species diversity and phylogenetic diversity increases with increasing plant diversity and phylogenetic diversity. Above- and belowground plant diversity responded differently to soil fertility gradient as well. Similar to previous studies, aboveground richness declined with increasing soil fertility; in contrast, the number of species found only belowground increased with fertility. Investigating the plant community assembly patterns above- and belowground revealed substantial differences - there is more evidence for biotic interactions, such as light competition aboveground, whereas abiotic and stochastic processes, such as soil nutrient gradients, soil pH, etc. dominate belowground. Results of this thesis suggest that by considering only aboveground vegetation we merely see the "tip of an iceberg", whereas real species coexistence occurs belowground. This thesis for the first time highlights the importance of belowground processes in the research of plant species coexistence and ecosystem processes.
Our current understanding about plant species diversity and coexistence is almost entirely based on studies of aboveground vegetation. In some species-rich grassland ecosystems, nearly 75% of plant biomass occurs belowground, however, little is known about below-ground processes due to difficulties in distinguishing between morphologically similar roots of different species. Belowground root systems are more extensive in space and more persistent in time than short-lived shoots, causing belowground species richness to be higher than aboveground per volume. In this thesis I explored the differences between the patterns of below-and aboveground plant diversity with adding new insights to the knowledge of mutualistic relationships between plants and root dwelling fungi and the functioning of plant communities as a whole. Application of next-generation sequencing revealed that belowground plant species richness can be up to twice as high as aboveground. By using the same root samples I identified arbuscular mycorrhizal fungi forming tight mutualistic relationships with plants and found that fungal species diversity and phylogenetic diversity increases with increasing plant diversity and phylogenetic diversity. Above- and belowground plant diversity responded differently to soil fertility gradient as well. Similar to previous studies, aboveground richness declined with increasing soil fertility; in contrast, the number of species found only belowground increased with fertility. Investigating the plant community assembly patterns above- and belowground revealed substantial differences - there is more evidence for biotic interactions, such as light competition aboveground, whereas abiotic and stochastic processes, such as soil nutrient gradients, soil pH, etc. dominate belowground. Results of this thesis suggest that by considering only aboveground vegetation we merely see the "tip of an iceberg", whereas real species coexistence occurs belowground. This thesis for the first time highlights the importance of belowground processes in the research of plant species coexistence and ecosystem processes.
Description
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Keywords
juurestik, taimed, liigirikkus, niidud, seened, mullaviljakus, root systems, plants, species richness, meadows, fungi, soil fertility