Arctic PhIr: Biological and geochemical controls on phosphorus in arctic tundra

The ability of terrestrial ecosystems to store carbon depends largely on nutrient availability, which affects both plant growth and decomposition rates. Phosphorus (P) is often a limiting nutrient, and P cycling in tundra ecosystems is widely assumed to occur primarily through biological pathways, in which biological P demand is met by enzymatic release of phosphate from organic molecules. However, this conceptual model does not account for iron (Fe) oxides, which may serve as nutrient traps that regulate phosphate solubility and serve as P sources or sinks under different redox conditions, even in organic soils. The processes controlling the quantity and bioavailability of oxide-bound P under different environmental conditions remain unclear, limiting our ability to predict how P availability might change with expected hydrological changes. Fluctuating redox conditions drive microbial transformation of Fe oxides and may also regulate P bioavailability. Thus, biological and geochemical controls over P dynamics may vary as a function of hydrology and redox regime across arctic landscapes. This project will use a sensor network to characterize redox and pH patterns in environments typical of low-arctic tundra and investigate biological and geochemical P competition across these gradients. The investigators will quantify competitive partitioning of P between abiotic (Fe oxides and other minerals) and biotic (microbial and plant) sinks. They will test the hypothesis that geochemical sorption and co-precipitation processes effectively compete with plant roots and microorganisms for phosphate in tundra soils. The study will provide the first assessment of the importance of geochemical versus biological controls on P bioavailability and how they might be altered by hydrological changes in these sensitive ecosystems.

This project is funded by NSF OPP Arctic Natural Sciences through Project #191455.
Principal Investigators: Elizabeth Herndon (U Tennessee/ORNL); Lauren Kinsman-Costello (Kent State), Michael Weintraub (U Toledo)
Project duration: 2019 - 2022

Geochemical regulation of ecosystem carbon storage

Elucidating the complex controls on ecosystem carbon storage is critical for predicting how earth systems will adapt to changing climate. Furthermore, managing ecosystems to increase carbon storage may partially offset carbon dioxide (CO2) emissions and protect future ecosystem sustainability. However, ecosystem representations that focus exclusively on biological components and disregard geochemical processes will fail to accurately represent ecosystem function. This research will “advance the understanding of complexity in biological and environmental systems” by elucidating a coupled element cycle across multiple scales that has implications for how carbon is sequestered in terrestrial ecosystems. This work aligns with ongoing efforts to translate molecular-scale characterization into ecosystem-scale understanding and predictive models. The two aims of the work are to 1) examine the processes by which elevated Mn may accelerate litter decomposition; and 2) determine the net effect of organo-mineral interactions on C storage.

This project is funded by DOE Oak Ridge National Laboratory Strategic Hire package to Herndon
Project duration: 2019 - 2021