Characterization and Dynamics of NaOH-Extractable Organic Phosphorus Species in Soils

Organic phosphorus (Po) plays a critical role in soil phosphorus (P) cycling, yet the behavior and fate of specific Po species remain poorly understood. In this study, ion chromatography coupled with inductively coupled plasma mass spectrometry (IC-ICP-MS) was employed to characterize NaOH-extractable Po species in two soil types, with a focus on their temporal dynamics and responses to soil degradation. Nine distinct phosphorus peaks were identified in soil extracts, of which four remain unidentified. Based on their occurrence patterns and sensitivity to environmental change, these Po species were classified into three groups: unstable species, detected only in fresh plant or algal materials; stable species, consistently present across all samples with minimal variation; and indicator species, exhibiting moderate sensitivity to environmental conditions. Notably, the indicator species α-glycerophosphate (α-gly) and an unidentified compound (P150) showed pronounced declines during degradation. Along a grassland degradation gradient, P150 concentrations decreased by 66% in highly degraded soils compared with non-degraded soils, while α-gly declined by 27%. In addition, IC-ICP-MS revealed a tenfold discrepancy between conventional colorimetric and direct Po measurements, indicating the dominance of recalcitrant macromolecular Po fractions in soils. These results provide new insights into the molecular-level dynamics of soil Po and highlight the importance of small-molecular Po species in sustaining soil fertility and ecosystem resilience.