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The importance of phenotypic plasticity for plant success under environmental change

The importance of phenotypic plasticity for plant success under environmental change

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LIU, Yanjie, 2017. The importance of phenotypic plasticity for plant success under environmental change [Dissertation]. Konstanz: University of Konstanz

@phdthesis{Liu2017impor-39950, title={The importance of phenotypic plasticity for plant success under environmental change}, year={2017}, author={Liu, Yanjie}, address={Konstanz}, school={Universität Konstanz} }

terms-of-use eng Environmental factors can change in space and time both in terms of the mean conditions and in terms of variability. Phenotypic plasticity is assumed to be an important mechanism leading to plant success under both natural and/or anthropogenic environmental change conditions. Yet, we still have a limited understanding of whether phenotypic plasticity contributes to the success of alien plant species under environmental change. Moreover, phenotypic plasticity of many functional traits associated with nutrient uptake and light capture are frequently implicitly assumed to be adaptive in many studies. However, the adaptive value has rarely been tested for most of them. Therefore, my thesis aimed to gain insights into how phenotyp-ic plasticity contributes to plant success under environmental change, specifically focusing on plant invasion under anthropogenic global change and nutrient fluctuations. Additionally, I also tested whether phenotypic plastic responses that are assumed to be adaptive are really adaptive, specifically focusing on the plastic response of specific leaf area (SLA) induced by changes in light intensity.<br /><br />First, I performed a meta-analysis to test whether there is a general pattern in invasive and native plant responses to environmental change in mean conditions. I established a plant da-tabase, which included 74 invasive alien plant species and 117 native plant species. I com-pared plastic responses in performance traits to increasing atmospheric CO<sub>2</sub> concentrations, increasing temperatures, increasing N deposition, and increasing or decreasing precipitation between invasive alien and native plants. I found that invasive alien plant species showed stronger positive responses to favourable environmental changes, particularly global warming and atmospheric CO<sub>2</sub> enrichment. My results suggest that, because of the higher plasticity of invasive alien plant species than native plant species, global environmental change may promote spread of invasive plants in the future.<br /><br />Second, I performed a multispecies greenhouse experiment to test whether alien and common plant species take more advantage of increases in nutrient levels and fluctuations therein than native and rare species. There were six nutrient-supply treatments that differed in the mean and temporal availability of nutrients. I compared plastic responses in biomass production, root allocation and root morphology to such nutrient treatments among seven common alien, seven rare alien, nine common native and six rare native plant species. I found that the plastic responses of biomass production, root morphology and root allocation to nutrient changes under mean conditions did not differ between alien and native plant species. However, I found that, compared to a constant high nutrient supply, alien plant species showed positive plastic responses in biomass production to large nutrient pulses, whereas native plant species showed negative plastic responses, possibly as a consequence of differences in plasticity of root traits. My findings suggest alien species might be become more dominant when fluctua-tions in nutrients increase. In this study, I did not find differences in plastic responses to nu-trient addition and fluctuations between invasive (i.e. common) and non-invasive (i.e. rare) alien species, possibly, because plants were grown in the absence of competition.<br /><br />Third, I used a multispecies greenhouse experiment to test whether invasive alien plant species might show higher plastic response and thus take more advantage of nutrient fluctuations than non-invasive alien, when grown in competition with native plant species. I grew ten pairs of invasive and non-invasive alien plant species under the same nutrient-supply treatments as used in the first greenhouse experiment, but this time in the presence of native competitors. I found that invasive alien plant species exhibited a significantly stronger increase in biomass production in response to high nutrient levels than non-invasive alien plant species. This is inconsistent with the findins of the first greenhouse experiment, where plants grew without competition. This suggests that responses to nutrient-supply patterns for single plants might not be representative for plants grown under competition. However, I also found that both groups of alien target species benefited proportionally less from nutrient addition overall than the native competitors. Surprisingly, the alien species, and particularly the invasive ones, suffered from nutrient pulses. These findings stongly suggest that it is not a general phenomenon that environmental variability promotes plant invasion.<br /><br />Finally, I performed a meta-analysis to test whether a phenotypic plastic response that is widely assumed to be adaptive – the increase in specific leaf area (SLA) induced by shading - is really adaptive. I compiled a database including data from 467 case studies using 32 publi-cations and two unpublished experiments, which measured the responses of biomass and SLA of 280 plant species to shading. I found that the potential higher ability of plants to capture light by increasing SLA under low-light conditions was not associated with the maintenance of biomass homeostasis in plant species, but rather with a greater reduction in biomass. This suggests that plasticity of SLA to shading might not constitute adaptive plasticity. Therefore, I argue that some of the plastic responses of plant species to environmental changes, which are frequently thought to be adaptive, might simply reflect passive responses to the environment, or may reflect indirect responses due to correlations with adaptive plasticity of other traits.<br /><br />To sum up, my thesis explored the importance of phenotypic plasticity for plant success under environmental change. My findings reveal that phenotypic plasticity could be linked to a certain extent to plant success under environmental change in space and time. The next steps in this field of research should be studies that systematically integrate the indirect influence on phenotypic plasticity of plants from plant species and other trophic levels, such as soil biota, herbivores and pollinators. My findings also suggest that more studies are needed to test explicitly whether the phenotypic plasticity of functional traits in response to a specific environmental cue is really adaptive, and thus contributes to plant success under environmen-tal change in time and space. 2017-09-01T08:23:48Z Liu, Yanjie 2017-09-01T08:23:48Z 2017 The importance of phenotypic plasticity for plant success under environmental change Liu, Yanjie

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