Microbial Community Assembly Processes in Agricultural and Natural Ecosystems

Abstract

Microbial communities can support plant and soil health through disease suppression, growth promotion, improving stress tolerance and increasing nutrient supply and cycling. The microbiome of crops has been suggested as a target to improve agricultural sustainability and crop performance. Targeted breeding efforts may allow for the selection of more robust crop microbiomes, lessening the need for additional agricultural inputs. However, how crop associated microbiomes assemble is still poorly understood. To more effectively engineer the microbiome, a more complete knowledge of the selection pressures that shape these communities over time and space is needed. Within this, an understanding of what is acting as biotic or abiotic filters and imposing these selection pressures is also needed. Once these aspects of microbial community assembly in crops are known, more effective selection of microbiomes can occur. In addition to agriculture, a more complete understanding of soil microbial community assembly processes in natural ecosystems is needed. Invasive species are expected to expend in both range and abundance with climate change. Invasive species cause decreases in local plant diversity and alter local soil microbial communities and ecosystem services. The invasive plant will also disturb native microbial community assembly processes. Understanding how invasive species impact soil microbial community assembly processes and the associated ecosystem services will provide vital information to aid in restoration efforts. Furthermore, when restoration might not be feasible, understanding these processes will allow for more accurate predictions of how ecosystem services will change and the proper remediation planning can then occur. However, the knowledge of how invasive species affect assembly processes is still unclear. This dissertation found that the primary factor affecting microbial community assembly processes in both agricultural and natural ecosystems was time. In the agricultural system, time was the growth stage of Brassica napus. In the native grassland, seasonal changes impacted bacterial and fungal assembly processes more than invasive biomass. Ecosystem services were also affected more by seasonal changes than invasive biomass. Given the annual cyclical nature of both plant growth stage and seasonal changes in a grassland, the patterns observed will likely endure from year to year.