Browsing by Author "Ala-Heikkilä, Veera Annika"

As biodiversity is declining globally, there is a crucial need to understand the connections between diversity and ecosystem functioning. Research has shown that diversity tends to lead to higher productivity, but our understanding of the underlying reasons is still limited. For example, biotic interactions with mycorrhizal fungi could cause these diversity effects in plant communities, but few studies have assessed the subject. In this thesis, I studied the impacts of arbuscular mycorrhizal symbiosis on diversity effects with three research questions. First of all, I aimed to determine whether mycorrhizal symbiosis affects the diversity–productivity relationship across plant communities. Secondly, I divided diversity effects into two parts: complementarity and selection effects. These effects can be determined statistically. Finally, I studied how different species within the community respond to diversity. To answer these questions, I conducted a greenhouse study with varying plant communities. I manipulated the plant species diversity and used a fungicide treatment to suppress mycorrhizal fungi. After the growing period, I measured the biomasses of the plants as an indicator of productivity. I tested the effectiveness and side effects of the fungicide by estimating mycorrhizal colonization rates in plant roots and by testing its effects on non-mycorrhizal plant species. The fungicide treatment did not affect diversity–productivity relationship nor diversity effects significantly. However, fungicide treatment failed to reduce the overall mycorrhizal colonization rate and had varying effects on different plant species. One of the plant species benefitted from species diversity whereas other species experienced either no effect or a negative effect of increased diversity. No specific trait explained the varying responses on diversity. More research is needed to understand plants’ complex responses to decreasing biodiversity and biotic interactions, as well as to clarify whether fungicide is a fitting method for mycorrhizal suppression studies.