Exploring the mechanisms of phosphorus uptake and recycling in soils using the stable isotope labeling technique

Researcher(s)

  • Cate Yeargan, Agriculture and Natural Resources, University of Delaware

Faculty Mentor(s)

  • Deb Jaisi, Interdisciplinary Science and Engineering Laboratory, University of Delaware, Newark, DE 19716, USA, University of Delaware

Abstract

Title: Exploring the mechanisms of phosphorus uptake and recycling in soils using the stable isotope labeling technique

Authors: Cate Yeargan, Devraj Maidali,  Prishu Gaire, and Deb Jaisi

 

Background: Phosphorus (P) is a key macronutrient required for plant growth, but its fate in soil is not yet fully understood. Understanding P uptake is critical to improve uptake efficiency and decrease P loading and loss from agricultural soils. Isotope labeling is one of the key approaches for tracking P uptake and fate. Here, we studied the fate of inorganic phosphate (Pi), using 18O-labeled Pi as a tracer in agricultural soil undergoing corn growth.

Method: 18O-labeled Pi was synthesized using 10% 18O water and P pentachloride and was surface sprayed on the soil undergoing corn growth. At different time points, topsoil was collected, and different pools of Pi were extracted using the Hedley extraction method and quantified using the molybdate blue method. Zirconium oxide (ZrO) resin was used to selectively isolate and concentrate the NaOH-Pi pool followed by cation exchange resin. The partially purified Pi in a 9:1 methanol: water solution was analyzed by Orbitrap mass spectrometry using negative ionization mode, MS/MS fragmentation, and m/z 70-90.

Results: NaOH-Pi was the largest Pi pool, followed by the H2O-Pi and HCO3-Pi pools, which are bioavailable Pi pools. In control soil, Pi concentrations stayed steady over the year. In treated soil, Pi concentrations declined, approaching control levels.  There was no significant difference in corn biomass content between control and treated soils, suggesting that excess Pi was most likely leached rather than taken up. ZrO resin sorption was near complete, but desorption was limited (~40%), for unclear reasons. Orbitrap IRMS analysis is ongoing to quantify Pi fate.

Conclusion: Excess Pi applied in soil most likely leached out of soil. Changes in Pi pool concentrations, paired with Orbitrap isotopic analysis, provide insights into the fate of P fertilizer in agricultural soil.