Plasticity to light in herbaceous plants and its importance for community structure and diversity
Date
2013-10-25
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Abstract
Kõigi roheliste taimede elu aluseks on küllaldane päikesevalguse omastamine. Ehituslik kohanemisvõime e. morfoloogiline plastilisus võimaldab taimedel muuta kõrguskasvu, lehtede arvu, pindala ja asetust ning seeläbi parematesse valgustingimustesse küündida. Seetõttu sõltub ka naabertaimede vaheliste suhete iseloom (allasuruvast konkurentsist kuni teineteise kasvu soodustamiseni) oluliselt taimeosade vastastikusest paigutamisest. Kuigi teooria ja mõneliigilised katsed on ennustanud, et plastilisuse mõju kooslusele peaks olema märkimisväärne, ei ole seost looduslikes tingimustes varem näidatud.
Taimede kohanemisvõime ulatuse hindamiseks kasvatasime katseaias erinevates valgustingimustes 46 liiki rohttaimi, uurisime lähemalt nende kasvu ja hindasime plastilise kohanemisvõime ulatuse. Et näha plastilisuse mõju taimekoosluste kujunemisele kasutasime andmeid 17 eriilmelisest niidukooslusest ning Laelatu puisniidul asuvatelt püsiruutudelt. Leidsime prooviruutudel kasvanud liikide keskmised plastilisuse hinnangud ning kõrvutasime neid samade alade liigirikkuse- jm. näitajatega. Selgus, et plastiliste taimeliikide kooskasvamisel oli taimede vastastikune allasurumine väiksem, taimed olid võrdsema kõrguskasvuga, kasvasid tihedamalt ja liigirikkus prooviruudul oli oluliselt kõrgem. Ka koosluse siseselt oli plastiliste isendite kooskasvamisel liigirikkus kõrgem.
Seda, et liigirikkad kooslused on mitmeti kasulikud (sh inimestele), on praeguseks mõistnud peale teadlaste ka paljud metsa-, põllu- ja riigimehed. Liigirikaste koosluste efektiivseks kaitsmiseks on vaja selget arusaamist sellest, mismoodi kooslused toimivad. Minu doktoritöö tulemused näitavad, et taimede valgustingimustega kohanemise võime on liigiomadus, mis otseselt ja oluliselt mõjutab parasvöötme rohumaade liigirikkuse kujunemist.
Solar radiation is an essential resource for all green plants. Most plants are capable of adjusting their height, number, area and inclination of leaves etc. according to illumination conditions (morphological plasticity) in order to achieve a better access to the light resource. On the other hand, interactions between neighbouring plants directly depend on their architecture, substantially shaped by plasticity. The possible effect of plastic acclimatization to light on community structure has been suggested by several authors but has not yet been studied in natural multi-species communities. We studied morphological plasticity and growth of 46 herbaceous species on an artificial light gradient in a garden experiment. We also used data on community diversity and structure from 17 grasslands in Estonia and performed several field studies in the species-rich Laelatu wooded meadow. Using plasticity estimates from garden experiment we estimated the average degree of plasticity for co-growing species in the studied communities. We found lower variability of shoot height, higher density of plant ramets and higher small-scale diversity in communities where species with high plasticity prevailed. Positive relationship between plasticity and diversity was also found within one community (Laelatu) – in locations with high concentration of high-plasticity species local diversity was significantly higher. There it was also possible to show that there is a direct link between plasticity and diversity – one that is not mediated by varying ramet density. Declining biodiversity has been a high-priority topic in nature conservation for years. For preserving effectively our species-rich plant communities we need a clear understanding of their functioning. The results of my thesis demonstrate that plants’ shoot morphological plasticity to light is a highly important trait for herbaceous species, enabling them to successfully co-exist in dense and diverse plant assemblages.
Solar radiation is an essential resource for all green plants. Most plants are capable of adjusting their height, number, area and inclination of leaves etc. according to illumination conditions (morphological plasticity) in order to achieve a better access to the light resource. On the other hand, interactions between neighbouring plants directly depend on their architecture, substantially shaped by plasticity. The possible effect of plastic acclimatization to light on community structure has been suggested by several authors but has not yet been studied in natural multi-species communities. We studied morphological plasticity and growth of 46 herbaceous species on an artificial light gradient in a garden experiment. We also used data on community diversity and structure from 17 grasslands in Estonia and performed several field studies in the species-rich Laelatu wooded meadow. Using plasticity estimates from garden experiment we estimated the average degree of plasticity for co-growing species in the studied communities. We found lower variability of shoot height, higher density of plant ramets and higher small-scale diversity in communities where species with high plasticity prevailed. Positive relationship between plasticity and diversity was also found within one community (Laelatu) – in locations with high concentration of high-plasticity species local diversity was significantly higher. There it was also possible to show that there is a direct link between plasticity and diversity – one that is not mediated by varying ramet density. Declining biodiversity has been a high-priority topic in nature conservation for years. For preserving effectively our species-rich plant communities we need a clear understanding of their functioning. The results of my thesis demonstrate that plants’ shoot morphological plasticity to light is a highly important trait for herbaceous species, enabling them to successfully co-exist in dense and diverse plant assemblages.
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Keywords
rohttaimed, valguse toime, kasv, liigirikkus, niidutaimed, autökoloogia, herbs, light effect, growth, species richness, meadow plants, autecology