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Testing the relative roles of competition and plant-soil feedback in explaining commonness and rarity of alien and native plant species

Testing the relative roles of competition and plant-soil feedback in explaining commonness and rarity of alien and native plant species

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MÜLLER, Gregor Simon, 2017. Testing the relative roles of competition and plant-soil feedback in explaining commonness and rarity of alien and native plant species

@phdthesis{Muller2017Testi-39902, title={Testing the relative roles of competition and plant-soil feedback in explaining commonness and rarity of alien and native plant species}, year={2017}, author={Müller, Gregor Simon}, address={Konstanz}, school={Universität Konstanz} }

2017-08-17T12:22:48Z Müller, Gregor Simon Why some species become common while others remain rare is a long-standing question in ecology. Yet, it has not lost any of its relevance. Particularly, the striking success of some invasive alien species has fuelled research interest in what drives such invasions. Understanding the underlying mechanisms that allow a species to become common is an important prerequisite to be able to predict and manage such phenomena. However, the success of some alien species may be driven by the same factors that help some native species achieve and maintain a wide distribution and high abundance.<br />Plant-soil interactions have been put forward as a potential mechanism that could explain why some species become common, while others remain rare. A growing number of studies acknowledge the role of plant-soil interactions in species performance, yet many questions remain unanswered. For example, competition may also play a role in explaining species success, and both factors may not act independently but work in concert to govern species performance. Moreover, the importance of plant-soil interactions relative to ecological factors like herbivores or disturbance has received little attention. Lastly, the question of whether alien and native species are similarly affected by these factors or if, for example, only common alien species generally profit from less negative plant-soil interactions (e.g. due belowground enemy release) is not fully clarified.<br />First, to disentangle the relative roles that plant-soil feedback and intraspecific competition play in plant performance, we conducted a multispecies greenhouse experiment with 30 common and rare alien and native plant species. We used a two-phase setup to first train the soils at increasing intraspecific frequency and then regrow the target species at increasing frequencies in these trained soils. Our results showed that increasing levels of intraspecific competition decreased plant performance regardless of species origin or commonness. Moreover, alien species suffered from negative plant-soil feedback in soils trained by high conspecific planting levels, but natives did not. This suggests that alien species may not generally be released from belowground enemies. Furthermore, species commonness does not seem to be linked to differences in plant-soil interactions or magnitude of intraspecific competition.<br />Second, we tested the roles of plant-soil feedback and competition on species population-level performance in a two-year mesocosm study with annual two-species communities grown at high and low sowing frequency and treated with or without fungicide. We found that alien and native species similarly profited from fungicide treatment and that alien species, but not natives, showed a higher per capita performance at low sowing frequencies. This highlights the role that generalist pathogens may play affecting natives as well as aliens. Furthermore, aliens may profit from high per capita performance at initial establishment.<br />Lastly, we performed a field experiment testing how disturbance and above and belowground enemies influence species establishment success. We found a strong positive effect of disturbance on establishment success regardless of species origin or commonness, and only weak effects of belowground enemy release for alien species. Thus, we found strong evidence for biotic resistance of grassland towards incoming species, and only a minor mediatory role for soil-borne enemies in combination with disturbance for establishment success of alien species.<br />In summary, my studies show that alien species may not always be released from belowground enemies, and that species commonness is not generally linked to plant-soil interactions or intraspecific competition. Moreover, assessing the relative role of plantsoil interactions under realistic conditions is crucial for gaining insight into when and under what circumstances plant-soil interactions are important for species performance. 2017-08-17T12:22:48Z Müller, Gregor Simon eng 2017 Testing the relative roles of competition and plant-soil feedback in explaining commonness and rarity of alien and native plant species

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