The influence of abiotic and biotic factors on small-scale plant community patterns and regeneration in boreonemoral forest
Date
2012-10-16
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
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.
Plants can perceive their close surrounding and adapt to those conditions. For example, it is known that plants can locate their roots into nutrient rich areas; and increase growth in the presence of symbiotic micro-organisms like arbuscular mycorrhizal (AM) fungi that help plants to acquire nutrients from soil. In addition, plants in forest understorey are highly influenced by overstorey and this can occur through the effects of tree and shrub litter. Despite this knowledge, we have still little information about the relative importance of abiotic and biotic factors (e.g. the ones listed above) in determining understorey productivity, regeneration success and species richness in natural ecosystem. Boreonemoral spruce forest with hazel sub-canopy and species-rich understorey was selected as a model system to fill abovementioned gaps in our knowledge. I found that high availability of soil nutrients and abundance of AM fungi enhances plant aboveground biomass, which implies to the importance of light competition among understorey plants. At the same time, soil nutrient content and the abundance of AM fungi did not influence plant belowground biomass. Plants seem to be able to acquire more nutrients directly from the soil when nutrient level is high or alternatively via symbiotic relationship with AM fungi when nutrient content is low. This mechanism seems to operate also at regeneration phase as I found that seedling growth of a characteristic forest plant species benefited from the presence of AM fungi when soil nutrient content was low. At the same time, seedling growth of a plant species occurring in a wide range of habitats was not influenced by AM fungi despite of soil nutrient content. In addition, the regeneration of the plant species in the understorey was highly influenced by presence and type of overstorey litter as I found that hazel litter is more beneficial to seedling growth and emergence than spruce litter. The effect of different factors, especially the effect of litter, leads to spatial differentiation in species composition in the forest understorey as I recorded twice as high herbaceous species richness under hazel compared to spruce. Results of this thesis lead to better understanding of forest understorey dynamics. Improved knowledge enables to preserve the species richness characteristic to forests as most of the of plant species growing in forests can be found in the understorey.
Plants can perceive their close surrounding and adapt to those conditions. For example, it is known that plants can locate their roots into nutrient rich areas; and increase growth in the presence of symbiotic micro-organisms like arbuscular mycorrhizal (AM) fungi that help plants to acquire nutrients from soil. In addition, plants in forest understorey are highly influenced by overstorey and this can occur through the effects of tree and shrub litter. Despite this knowledge, we have still little information about the relative importance of abiotic and biotic factors (e.g. the ones listed above) in determining understorey productivity, regeneration success and species richness in natural ecosystem. Boreonemoral spruce forest with hazel sub-canopy and species-rich understorey was selected as a model system to fill abovementioned gaps in our knowledge. I found that high availability of soil nutrients and abundance of AM fungi enhances plant aboveground biomass, which implies to the importance of light competition among understorey plants. At the same time, soil nutrient content and the abundance of AM fungi did not influence plant belowground biomass. Plants seem to be able to acquire more nutrients directly from the soil when nutrient level is high or alternatively via symbiotic relationship with AM fungi when nutrient content is low. This mechanism seems to operate also at regeneration phase as I found that seedling growth of a characteristic forest plant species benefited from the presence of AM fungi when soil nutrient content was low. At the same time, seedling growth of a plant species occurring in a wide range of habitats was not influenced by AM fungi despite of soil nutrient content. In addition, the regeneration of the plant species in the understorey was highly influenced by presence and type of overstorey litter as I found that hazel litter is more beneficial to seedling growth and emergence than spruce litter. The effect of different factors, especially the effect of litter, leads to spatial differentiation in species composition in the forest understorey as I recorded twice as high herbaceous species richness under hazel compared to spruce. Results of this thesis lead to better understanding of forest understorey dynamics. Improved knowledge enables to preserve the species richness characteristic to forests as most of the of plant species growing in forests can be found in the understorey.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
metsad, alustaimestu, liigiline koosseis, abiootilised tegurid, biootilised tegurid, forests, ground vegetation, species composition, abiotic factors, biotic factors