Oxygen Stable isotopes in phosphate: what is next?

Oxygen isotopes in phosphate (δ¹⁸Oₚ) have rised interest as powerful tracers for environmental studies, offering valuable insights into phosphorus cycling, biological activity, and potential phosphate source tracing in diverse environments. By January 2025, more than 180 peer-reviewed studies have explored δ¹⁸Oₚ applications in Environmental Sciences, underscoring the interest in this tool, but also its limited application. Broader adoption of δ¹⁸Oₚ analysis is hindered by challenges such as the complexity of sample preparation, uncertainties in isotopic data interpretation, and the difficulty of identifying all endmembers in field-based studies.

Recent advancements in high-resolution mass spectrometry (HRMS), allowing the isotopic measurements of oxyanions at natural abudances, have addressed key technical limitations. This innovation facilitates the analysis of smaller samples, but recent research highlights the critical need for thorough sample preparation to ensure reliable results. These advances lay the groundwork for more extensive δ¹⁸Oₚ applications, particularly since HRMS are becoming more and more widespread.

Central to δ¹⁸Oₚ studies is the process of phosphoryl transfer, a fundamental mechanism in numerous biological processes. Changes in the isotopic composition of oxygen in phosphate promoted by phosphoryl transfer is considered to reflect the metabolic status of living cells, positioning δ¹⁸Oₚ as a potential “thermometer” for assessing organism metabolic “health”. This capability is particularly evident in soil incubation experiments, where the extent of oxygen exchange during phosphoryl transfer recorded in the microbial phosphate pool correlates with respired CO₂. Such findings highlight δ¹⁸Oₚ's potential to link phosphorus cycling to carbon cycling, providing new perspectives on ecosystem functioning.

To harness this potential, future research should prioritize ¹⁸O labelling approaches in controlled incubation experiments integrating ancillary data, such as CO₂ flux measurements, to elucidate the mechanistic links between metabolic activity and changes in isotopic values. Complementary field studies, incorporating detailed assessments of δ¹⁸Oₚ alongside CO₂ and other environmental parameters, are essential for validating laboratory findings and expanding their relevance to complex natural systems.

By addressing these challenges and leveraging recent technical innovations, δ¹⁸Oₚ can emerge as a robust tool for deciphering phosphorus dynamics, their connection with metabolic processes, and their broader role in environmental systems.