Supervisor: Professor Kristjan Zobel
Opponent: dr Jitka Klimešova (Institute of Botany of the Academy of Science of the Czech Republic)
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.