Collaborative Research: Biological and geochemical controls on phosphorus bioavailability in arctic tundra

Phosphorus is an essential nutrient for life, but in some environments it is in short supply, putting limits on plant growth and decomposition. Plants and microorganisms take up phosphorus from the water in soil in the form of dissolved phosphate, which can also be removed from solution by binding to soil minerals. In particular, iron oxide minerals strongly bind phosphate and may regulate its availability to plants and microorganisms. This project will investigate how geochemical and biological systems compete for phosphate in arctic tundra soils near Toolik Field Station, Alaska, where soil warming and permafrost thaw are altering carbon and water budgets, which in turn affect soil moisture and nutrient availability. This research will determine how soil properties can affect this competition for phosphate, with broad consequences for plant growth and carbon dynamics in Arctic terrestrial ecosystems. This project also supports two early career scientists, a postdoctoral scholar, and multiple graduate and undergraduate students. Furthermore, all participants will design data-driven educational activities (DataNuggets), which will be used to communicate scientific results across multiple platforms.

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 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.