RUI: SG: Source or Sink? Do Plant-Microbial Interactions Determine the Direction of Carbon Flux During the Wet Phase of Northern Peatlands?

Ball State University, Muncie IN

Investigators

Abstract

Biofilms are communities of microorganisms, which include algae, fungi, and bacteria - organisms that grow in close association in aquatic environments. Compared to our understanding of biofilm ecology in most other environments, our knowledge of microbial interactions within wetlands is lacking. This knowledge gap is particularly evident in peatlands, a common landscape feature at northern latitudes. In part because of thick organic soil layers that lock up significant amounts of nutrients, northern peatlands are rich in carbon and poor in other nutrients. Plants such as mosses that can tolerate low nutrient availability produce a large fraction of annual biomass accumulation in peatlands, and this decomposes slowly. Over time, an imbalance between plant growth (primary production) and microbial decomposition leads to the accumulation of organic matter as peat. This small grant (SG) project will study peatlands at the Bonanza Creek Long-Term Ecological Research (LTER) site in Alaska during periods when they are inundated with water. The research will assess how between plant- and microbial biofilm-mediated activities impact the amount of carbon that gets stored in peat under this wet phase, and how much carbon is released into the atmosphere. In addition to charting new conceptual ground in ecosystem science, this project will provide research experiences for undergraduate students from under-represented groups and train two graduate students. Microbial biofilms are comprised of autotrophic (algae) and heterotrophic (bacteria and fungi) microorganisms that play a key role in aquatic ecosystem function. Heterotrophic biofilms are responsible for releasing carbon dioxide (CO2) to the atmosphere, whereas autotrophic biofilms take up CO2 during photosynthesis. The overall influence of biofilm composition on ecosystem carbon (C) emissions is determined by the exchange of resources among microorganisms, including algae, bacteria, and fungi. Autotrophs rely on heterotrophs to recycle nutrients, and heterotrophs rely on autotrophs for C that is fixed during photosynthesis, unless energetic requirements are met by outside sources. In peatland ecosystems with high water content, vascular plants and mosses have the potential to shift the metabolic balance of the microbial biofilm in favor of heterotrophy by providing C subsidies that allow heterotrophs to outcompete autotrophs for available nutrients. Given that some plant subsidies are more easily used by heterotrophs than others, the ability for plants to facilitate microbial activity may depend on plant community composition. However, the impact of plant community structure on microbial biofilms has not been widely studied in peatlands. As a result, it is difficult to predict how shifts in plant communities, such as those occurring with climate change, influence the C balance of northern peatlands. This project will use a combination of nutrient and organic matter manipulations at the Bonanza Creek LTER site to determine the extent to which organic C subsidies from plant communities govern ecosystem C flux by regulating the composition of microbial biofilms in northern peatlands. It is predicted that shifts in plant composition that favor labile C subsidies will increase CO2 emissions by promoting heterotrophic activity and reducing algal photosynthesis. In this condition, algae are no longer able to mitigate the effects of heterotrophic respiration leading to greater CO2 flux from the system. Alternatively, in the presence of less labile plant subsidies, heterotrophic microorganisms rely on algal sources of organic matter for metabolism within the biofilm. In this condition, algal photosynthesis mitigates CO2 emissions associated with heterotrophic respiration. Nutrient-rich plant subsidies, by contrast, could alleviate nutrient limitation of the biofilm resulting in greater algal biomass and CO2 uptake. The project will provide training opportunities for two masters students and several undergraduates, including members of underrepresented groups in science recruited through the NSF-funded Louis Stokes Alliance for Minority Participation Consortium in Indiana. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.