|The use of microbes for biological control of plant diseases represents an environmentally friendly and promising approach. Plant diversity is known to increase numerous ecosystem functions and also increases the resistance of soils to pathogens by increasing the abundance of essential microbes. However, to effectively antagonize soil-borne pathogens, bacteria not only need to produce antibiotics in sufficient amounts, but also need to successfully compete for nutrients and niches on the root surface, and escape predation. However, the extent to which each of those parameters impacts rhizosphere microbial functioning is not fully understood.
This thesis aimed at a mechanistic understanding of the effect of plant diversity and plant community structure on the abundance and activity of soil bacteria responsible for soil-borne plant disease suppression.
First, I analyzed whether plant diversity per se or plant functional group affiliation, plant identity or interaction effects are the main drivers of biocontrol bacteria and their activity in producing antifungal compounds. Second, I investigated abiotic factors and protozoan predation as mediators of plant community composition effects on plant-disease suppression.
Results of this thesis proved biocontrol bacteria in addition to abiotic soil parameters to be important determinants of pathogen suppression. The results underline the role of plant diversity in driving soil disease suppression, but further indicate that plant diversity (and functional group) effects are mediated by specific plant identity and plant-plant interaction effects. Moreover, the results underline the assumption that plant community composition, soil abiotic properties and microbial communities being antagonistic to soil pathogens are linked and interactively shape the suppressive potential of soils.
Results of this thesis represent an important step in unravelling the complexity of mechanisms linking plant community composition to plant disease suppression.
Choosing specific plant communities may enable to manipulate rhizosphere environmental conditions, thereby fostering microbial establishment in the rhizosphere and increase the disease suppressive potential of soils.