| Studies addressing soil microbial communities (SMC) have mostly emphasized particular soil organisms such as arbuscular mycorrhizal fungi (AMF) or soil pathogens within a single habitat. The main goals of my dissertation were to better understand how the interaction between plants and SMC vary across habitats of contrasting abiotic and biotic conditions, and address the role of whole SMC as well as distinct components of SMC. My study took place in the Central Cordillera in Colombia, which is a heterogeneous agricultural landscape comprised of tropical pre-montane forest fragments embedded in highly fertilized, agricultural monocultures, mainly sun-grown coffee plantations and pastures. I worked with SMC, and plants that are common in three contrasting habitats: pastures (Brachiaria grass), coffee plantations (coffee), and forest fragments (forest tree species).;I first tested for the effects of whole-SMC (i.e. all microorganisms in the soil) on plant growth, and found that SMC from the three contrasting habitats had differential and substantial effects on plant growth both in the greenhouse and in the field. Furthermore, fast-growing plant species (Brachiaria grass and pioneer forest trees) benefited from "away" (habitats where plant species rarely occur or do not occur at all) compared to "home" (habitats where plant species typically occur) SMC, while slow-growing shade tolerant forest tree species benefited the most from home SMC. I then evaluated how plants were affected by two main components of SMC: potentially mutualistic AMF, and likely antagonistic non-AMF soil organisms. I found that most plants grew significantly better with non-AMF microbes from away, compared to home habitats, while showing limited response to AMF from different habitats. Finally, I tested for plant-soil feedback for both AMF and for non-AMF soil microbes and found that feedbacks driven by AMF were weak, while feedbacks driven by non-AMF soil microbes were significantly negative. Furthermore, feedbacks were only significant for non-native species Brachiaria grass and coffee, while being weak for forest tree species.;Together, these results suggest that plant-soil dynamics have been severely disrupted with the replacement of tropical forest for agriculture, and advocate for future studies on non-AMF soil microbes, which have significant impacts on plant communities but remain largely understudied. |
