The influence of aboveground diversity on plant-microbe interactions: insights from the field to agriculture.

Understanding species coexistence in diverse plant communities is a central aim of theoretical ecology. Similar to Janzen-Connell effects reported in tropical forests, negative Plant-Soil-Feedback and Negative-Density-Dependent type effects have recently been implied to promote diversity in temperate grasslands by preventing conspecific species from repeatedly occupying the same site. I, therefore, use a range of methodological approaches (observational, experimental, long-term biodiversity trials) to explore plant-microbe interactions from natural ecosystems and apply this knowledge, ‘learned from nature,’ within an agricultural and sustainability framework. In natural grasslands, I show root-associated mycobiomes are host-specific, driven by phylogenetic host distance operating at the level of plant functional group (i.e. grasses and forbs), and a positive correlation between local plant density and pathogenic fungal diversity, suggesting host-specific pathogens select for rare species by elevating mortality when plant density is high. Next, host-specificity of the mycobiome is weaker in low diversity grasslands, implying the strength of host-specificity could be important for overall plant diversity. I build on these findings and test for within species host-specificity and NDD across a biodiversity gradient in agricultural production systems. I demonstrate vast potential to exploit beneficial plant-microbial interactions both within and between crop cycles with evidence to imply mixing of within species cultivars could dilute the accumulation of soil-borne pathogens. Finally, I explore the effect of management strategies, creating an intrinsic biodiversity gradient, on soil-microbiomes in the world’s largest agricultural system, palm oil. I show that increasing the diversity of the understory in oil palm plantations causes shifts in microbial diversity and composition. I conclude knowledge of plant-microbe interactions will enable improved predictions of vegetation dynamics, including nature restoration, and incorporation of this framework into agri-ecosystems could see a shift of conventional agriculture to microbe driven self-sufficient systems and ultimately increase overall sustainability.