Collaborative Research: BoCP-Design: US-South Africa: Turning CO2 to stone: the ecosystem service of the oxalate-carbonate pathway and its sensitivity to land use change

Mitigation of global warming requires a complete understanding of carbon exchange between the atmosphere and the land. Near-surface terrestrial carbon storage typically focuses on above-ground plants and organic carbon in soils, even though these forms of carbon are relatively unstable. Calcium carbonate (CaCO3) is a mineral that is regularly overlooked as a long-term and stable carbon store in soils.

In dry environments where plants are rich in calcium oxalate, certain bacteria and fungi can decompose the calcium oxalate in dead plant material, which can lead to the formation of CaCO3. This oxalate-carbonate pathway (OCP) provides a natural and potentially rapid way to sequester atmospheric CO2-carbon as solid CaCO3. This project will investigate how loss of biodiversity through land-use change and agricultural practices may reduce the amount of carbon that is transformed into CaCO3.

The project will develop an international team of ecologists, soil scientists, and geochemists through a series of fieldtrips, graduate student exchanges, and work packages that uses a multidisciplinary approach to understanding the importance and resilience of OCP ecosystems within the Greater Cape Floristic Region of South Africa. The project aims to develop a toolset that can ultimately be applied to investigate other candidate ecosystems worldwide.

Many such ecosystems are being converted to agriculture but are only marginally productive. Knowledge generated from this project will be shared with land users to inform decisions on land conversion, the potential valuation of carbon, and how this could be applied to improve monetary yields.

This project will investigate how the loss of functional biodiversity limits sequestration of carbon by the OCP in two important ways: 1) removal of native, calcium-oxalate rich vegetation (through farming and/or overgrazing) and physical disruption of giant termite mounds (through deep tillage) limits the supply of calcium-oxalate to the soil, and 2) loss of soil microbial diversity limits the breakdown of available calcium-oxalate. The interdisciplinary project will use eDNA-based functional biodiversity methods to identify the soil microbial assemblage that is the cornerstone of the proposed carbon sequestration pathway and how it changes upon disturbance; monitor the soil pore space apparent respiratory quotient (ratio of CO2 produced to O2 consumed) to spatially and temporally resolve the OCP non-destructively in soils; use stable Ca isotopes to trace the movement of calcium through plants and soils to help evaluate the time-integrated importance of the OCP; and develop a method for near and mid-infrared spectroscopy to measure Ca oxalate and calcite concentration that does not rely on prior dissolutions or precipitation.

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.