Root exudates induced coupled carbon and phosphorus cycling in a soil with low phosphorus availability

Background and aims: The amount and type of root exudates can influence P availability in the rhizosphere directly by desorption or dissolution of soil minerals, or indirectly by decomposition of soil organic matter (SOM). This study aimed to determine the mechanisms by which specific root exudates influence the distribution and availability of P in soils with low P availability. Methods: Water, glucose, alanine, and oxalate were delivered through a simulated root into soils for 15 days. Zymography and planar optodes were used to image potential phosphatase activity, and O₂ and pH distribution, respectively. Soils were analyzed for resin extractable inorganic P (P_i), dissolved organic C (DOC), water soluble Fe, and Al, and microbial community structure. Characterization of SOM and P were conducted using ultra-high resolution mass spectrometry and ³¹P solution nuclear magnetic resonance (NMR), respectively. Results: The addition of oxalate resulted in the greatest resin extractable P_i, DOC, and water-soluble Fe, and Al compared to the other exudates suggesting destabilization of mineral associated organic matter (MAOM) and release of organic P (P_o). Both ³¹P solution NMR and ultra-high resolution mass spectrometry analysis provided evidence of mineralization of P_o released from the destabilization of MAOM. Conclusion: The study demonstrates the important role microbial and plant-derived metal chelating ligands play in destabilizing MAOM, releasing SOM and importantly Po, that when mineralized may contribute to increasing Pi availability in soils with low P availability.