Soil phosphorus transformations along two long-term chronosequences with contrasting climate in south-western Australia

Background: Soil organic phosphorus (P) and its chemical nature change markedly during long-term pedogenesis, but how variation in ecosystem water balance and associated differences in vegetation impact such transformations remain unclear. Methods: We used solution P-31-nuclear magnetic resonance (P-31-NMR) spectroscopy to assess the chemical nature of soil organic P along two > 2-million-year coastal sand dune chronosequences in south-western Australia characterised by contrasting ecosystem water balance. We sampled soils from the progressive and retrogressive stages of the ecosystem along the wetter Warren and drier Jurien Bay chronosequences. Results: Organic P was a much greater proportion of the total soil P in the wetter Warren than the drier Jurien Bay chronosequence. However, the composition of soil organic and inorganic P detected by P-31-NMR spectroscopy was similar in the two chronosequences. Orthophosphate and simple phosphomonoesters were the dominant P species, and their proportional importance increased as soils aged, constituting > 80% of soil total P in the late stages of pedogenesis. However, no higher-order inositol phosphates were detected along either chronosequence, presumably due to the sandy texture and limited sorption capacity of the soils. Conclusion: Our results provide evidence that ecosystem water balance has little impact on the long-term soil organic P transformations during pedogenesis in south-western Australian dune sequences.