Macro-manipulation and micro-response: How climate changes shape critical interactions between plant roots and soil microbial communities
Plant roots influence belowground ecosystem function through many avenues, including root morphology and chemistry, exudate quantity and composition, molecular signaling, and interactions with belowground soil organisms. These effects shape not only soil community composition, but also soil biogeochemical functions and food web interactions, with strong follow-on impacts on greenhouse gas fluxes (e.g., CO2, CH4, N2O), nitrogen cycling, and carbon storage. Recent climate change manipulation studies suggest that these root and soil microbiome interactions are significantly altered by increased warming, drought, and elevated CO2. But what are the mechanisms that underlie climate-induced changes to soil structure and function? To gain a predictive understanding of climate change effects and ecosystem responses, ecosystem ecology needs an explicit framework for linking root effects (morphology, growth, exudation) with soil microbes and biogeochemical cycling. Beyond elucidating fundamental relationships, a key component of representing these interactions will be effective scaling – a difficult but critical task if we aim to understand the complex soil environment, both now and in the future.
We will present results collected across a range of physical and temporal scales and from multiple ecosystem types that illustrate how changes in climate affect belowground community function and root-microbe interactions. Our approaches span molecular to ecosystem scales, including molecular microbiology, novel isotope tracing approaches of root exudates and belowground communities, geochemical characterization of soil organic matter, resilience of soil food webs, and biogeochemical process rates. For example, we will show how presence of live roots significantly alters abundance, composition, and functional potential of soil microbial communities (assessed by both metagenomic and transcriptome sequencing) and that root effects on processes such as soil decomposition (e.g., via 'priming'), are dependent upon plant growth stage and drying stress. Evidence from a field-based mesocosm experiment also suggests that, by modifying soil C supply, plant species with different root traits shape the response and composition of belowground communities under disturbances such as extreme drought. Drought also affected soil food webs and microbial community composition, but intriguingly, presence of a plant increased the resilience and biomass of several functional groups in the soil food web. In a dryland experiment, warming induced changes to photosynthesis, root respiration, rhizodeposition greatly reduced soil CO2 efflux, while altered precipitation caused dramatic soil community composition shifts that mimicked the effects of intense physical disturbance. Taken together, these results underscore the complex and important role root-microbe interactions play in determining ecosystem response to environmental change.