PhD defence

Above- and belowground interactions in Jacobaea vulgaris: zooming in and zooming out from a plant-soil feedback perspective

• X. Liu

Date

Wednesday 15 May 2024

Time

11:15 - 12:00

Location

Academy Building
Rapenburg 73
2311 GJ Leiden

Supervisor(s)

• Prof.dr.ir. T.M. Bezemer
• dr. K. Vrieling
• dr.ir. S.T.E. Lommen

Summary

In this thesis, I focused on the above- and belowground interactions in J. vulgaris. I unraveled the temporal variation of negative plant-soil feedback (PSF) and examined the effects of root-associated bacteria on plant performance and its aboveground herbivores. Furthermore, I tested the role of PSF in relation to plant population structure, and test the relative importance of soil legacy effects under natural conditions. The results presented in this thesis demonstrate that changes in plant sensitivity and in the soil microbiome, particularly in a decline in the relative abundance of beneficial and an increase in the relative abundance of detrimental bacteria in “away” soil compared to “home” soil, during the feedback phase subsequently influence the PSF (Chapter 2). Although bacteria isolated from the roots of J. vulgaris can negatively affect plant performance, the inoculum can indirectly affect the preference of an aboveground herbivore, T. jacobaeae, and it can affect other plant species as well. Therefore, the bacteria used in the research in this thesis may not be used for biological control of common ragwort (Chapters 3 and 4). In addition, another group of biotic drivers of PSF, soil nematodes can mediate plant-plant interactions between J. vulgaris and other plant species, but this is often in favor of J. vulgaris (Chapter 5). In my field work, I uncovered that even though soil legacy effects are detectable under natural conditions (Chapter 7), the distance- and density-dependent seedling recruitment patterns of J. vulgaris in the field were not soil-mediated (Chapter 6). In summary, this thesis sheds light on the often overlooked temporal dimension of PSFs and demonstrates that changes in the sensitivity of responding plants and changes in soil microbes are underlying drivers. The insights gained from PSFs and above- and belowground interactions have the potential to reshape traditional approaches used for the biological control of invasive plants. Lastly, this thesis highlights the context-dependency of PSFs under natural conditions, emphasizing the need for experiments to transition from indoor to outdoor settings, and to considering various influencing factors simultaneously.

PhD dissertations

Approximately one week after the defence, PhD dissertations by Leiden PhD students are available digitally through the Leiden Repository, that offers free access to these PhD dissertations. Please note that in some cases a dissertation may be under embargo temporarily and access to its full-text version will only be granted later.

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