Plant-microbe interactions influence ecosystem processes: the role of roots and mycorrhizal fungal hyphae on terrestrial carbon dynamics

Plant-microbe interactions shape ecosystem processes such as productivity and decomposition of organic matter. Plants interact with mycorrhizal fungal hyphae to acquire nutrients from soil in exchange for plant-assimilated carbon. The mycorrhizal interaction is therefore a key influence on ecosystem carbon dynamics. Mycorrhizal fungi are key players in soil carbon cycling as they stimulate plants to allocate carbon belowground, and mycorrhizal fungal hyphae interact with microbial decomposers of soil carbon. However, there are few studies on mycorrhizal fungal hyphal interactions with roots and soil organisms in light of soil carbon accrual and release, important ecosystem processes. In my doctoral research, I examined interactions among plants, mycorrhizal fungal hyphae, and soil microbes in order to better understand the role of mycorrhizal fungal hyphae in soil C dynamics through combining models with experiments. In my first chapter, I discussed the direct role of mycorrhizal fungi on organic matter decomposition and subsequent shifts in soil carbon. I compared the effect of mycorrhizal hyphal decomposition to decomposition by free-living microbes using a carbon simulation model. In my second chapter, I tested how roots and mycorrhizal fungal hyphae indirectly affect decomposition of organic matter through interactions with free-living microbes. I found non-additive effects of roots and mycorrhizal fungal hyphae on soil microbial activity and hypothesized the effects were driven by nutrient demand. Thus, in my third chapter, I examined microbial decomposition of carbon and nutrient substrates across a range of root and mycorrhizal hyphal influence. My dissertation advances the field of ecosystem ecology by evaluating the role of plant-microbe interactions in soil carbon dynamics.